VEGETATION CHANGES AFTER 12 YEARS IN FOUR PRIVATE

RANCHES UNDER SHORT-DURATION AND CONTINUOUS

GRAZING SYSTEMS IN CHIHUAHUA, MEXICO

by

FRANCISCO JAVIER GONZALEZ GONZALEZ, B.S., M.S.

A DISSERTATION

IN

LAND-USE PLANNING, MANAGEMENT AND DESIGN

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

DOCTOR OF PHILOSOPHY

Approved

Mukaddes Darwish Chairperson of the Committee

Michael Galyean

Eduardo Segarra

Mark Wallace

Accepted

John Borrelli Dean of the Graduate School

August, 2006

Copyright 2006, Francisco Javier Gonzalez Gonzalez

ii

ACKNOWLEDGEMENTS

First, and foremost I would like to thank God because with him anything is

possible. I also express my gratitude to Dr. Mukaddes Darwish, chair of my

graduate committee for the opportunity she gave me to work with her, for her

support and encouragement to me, and for her example. To the other members

of my committee, Drs. Mark Wallace, Mike Galyean, and Eduardo Segarra, thank

you for this collaboration and your contribution in helping ensure that this work

was completed. I especially thank Drs. Galyean and Segarra for their support

through the tough times.

My deepest gratitude to the Consejo Nacional de Ciencia y Tecnologia

(CONACYT) and the Instituto Nacional de Investigaciones Forestales Agrícolas y

Pecuarias (INIFAP) for their financial support during the entire period of study.

My sincere gratitude is extended to Ing. Jesus Almeida, Lic. Federico

Terrazas, my friends Jaime Jeffers and Ing. Carlos Prado for permitting this study

to be conducted on their ranches.

Also I thank the following people for their help before and during the study:

Ing. Octavio Nuñez for his help in conducting the field work; and Drs. Alicia

Melgoza, Santos Sierra and Jorge Jimenez for their advice in organizing and

analyzing the data.

iii

I thank the following friends for their support, friendship and prayers:

Rogelio and Diana Carrera; Alejandro and Beatriz Meza; Gerardo and Beatriz

de la O, and all the people who helped me with their prayers.

Special thanks to Ing. Antonio and Enriqueta Chavez for their friendship

and moral support during all these years.

Also, thanks must be given to Dr. Sherman Phillips for his invaluable help

in editing this document and his friendship.

I express my appreciation to the Texas Tech Graduate School staff for

their fairness and financial support during the last year, especially to Drs. Ralph

Ferguson and John Borelli.

Finally I must thank my wife Bertha, my daughter Palmira, and my sons

Octavio and Eduardo for their incredible encouragement, support, and love

during all this time, because without them this work would have not been

completed.

iv

TABLE OF CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACT v

LIST OF TABLES vi

LIST OF FIGURES viii

LIST OF ABBREVIATIONS AND ACRONYMS ix

CHAPTER

I. INTRODUCTION 1

II. LITERATURE REVIEW 7

Short-Duration Grazing 8

Vegetation Changes 17

Cover 18

Forage Production 20

Density 23

III. VEGETATION CHANGES AFTER 12 YEARS IN FOUR

PRIVATE RANCHES UNDER SHORT-DURATION AND

CONTINUOUS GRAZING IN CHIHUAHUA, MEXICO. 27

Introduction. 27

Material and Methods 28

Results 38

Discussion 60

IV. CONCLUSIONS AND RECOMMENDATIONS 71

LITERATURE CITED 77

v

APPENDIX

A. VEGETATION SAMPLING TABLES 86

B. STATISTICAL ANALYSIS OUTPUTS 105

C. GLOSSARY 119

vi

ABSTRACT

With the objective to evaluate the vegetation changes over 12 years in

four ranches under Short-Duration (2 ranches) and Continuous (2 ranches )

grazing systems, a vegetation survey study was conducted in the fall of 1993,

1994, and 2005. Vegetation information was collected related to herbaceous

basal cover and shrub aerial cover, grass forage production, and plant density.

Vegetation was divided by functional groups to facilitate the analysis. The

perennial grasses functional group was the most consistent and reliable

functional group over time. Annual grasses and annual and perennial forbs were

important in the first year but tended to disappear in later years. Short-Duration

grazing had a higher perennial basal cover than the traditional system (P=0.059).

However, the magnitude of the decrease was greater in Short-Duration than in

Continuous grazing. A difference in forage production was found between

grazing systems (P=0.006). Ranches under continuous system had the highest

and the lowest production. The presence of Lehmann lovegrass in one of the

ranches under Continuous grazing accounted for a large proportion of forage.

A severe drought in 5 out of 12 years affected the response of vegetation,

and the effect of grazing system was likely diminished by the drought. Short-

Duration stocking rates were greater than those used in Continuous grazing.

Nevertheless, due the range condition in the Continuous treatment, the stocking

rates were also considered high. The stocking rates and drought conditions

affected the vegetation response of the grazing systems evaluated in this study.

vii

LIST OF TABLES

3.1 Basal cover (%) of perennial grasses in four ranches under two different grazing systems in Chihuahua, Mexico. 40 3.2 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 1. 42 3.3 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 2. 44 3.4 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 3. 46 3.5 Basal (grasses and forbs) and aerial (shrubs and suffrutescents) cover (cm) of species present in sampled transects categorized by functional groups in Ranch 4. 49 3.6 Basal cover (%) of by functional groups in four ranches under Short Duration (SD) and Continuous (CG) grazing management in Chihuahua Mexico. 52 3.7 Eigenvectors and weighed averages for the significant components resulted from a PCA conducted in 1993 and 2005 for vegetation changes in ranches with different grazing systems. 54 3.8 Forage production (kg DM/ha) in four ranches managed under Short Duration (SD) or Continuous (CG) grazing systems in Chihuahua, Mexico. 58 4.1 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 1 87 4.2 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 1 88 4.3 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch1 89

viii

4.4 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 2 90 4.5 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 2 91 4.6 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 2 92 4.7 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 3 83 4.8 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 3 94 4.9 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 3 95 4.10 List of species sampled in Fall 1993; Cover (cm/1200 cm) length Ranch 4 96 4.11 List of species sampled in Fall 1994; Cover (cm/1200 cm) length Ranch 4 97 4.12 List of species sampled in Fall 2005; Cover (cm/1200 cm) length Ranch 4 98 4.13 Ranch 1 list of species sampled ; Density (plants/m2) 99 4.14 Ranch 2 list of species sampled ; Density (plants/m2) 100 4.15 Ranch 3 list of species sampled ; Density (plants/m2) 101 4.16 Ranch 4 list of species sampled ; Density (plants/m2) 102 4.17 Forage production (kg DM/ha): Ranch1 103 4.18 Forage production (kg DM/ha): Ranch 2 103 4.19 Forage production (kg DM/ha): Ranch 3 104 4.20 Forage production (kg DM/ha): Ranch 4 104

ix

LIST OF FIGURES

3.1 Localization of Chihuahua State in Mexico. 29 3.2 Pasture distribution and vegetation type in Ranch 1. 30 3.3 Pasture distribution and vegetation type in Ranch 2. 31 3.4 Former pasture distribution and vegetation type in Ranch 3. 32 3.5 Former pasture distribution and vegetation type in Ranch 3. 34 3.6 Rainfall pattern (mm) of four ranches under Short Duration (SD) and Continuous (CG) grazing management in Chihuahua, Mexico. 39 3.7 Perennial grasses basal cover (%) in four ranches under Short Duration (SD) or Continuous (CG) grazing management in Chihuahua, Mexico. 53 3.8 Principal component analysis of functional groups associated with management system at four ranches in Chihuahua, Mexico in 1993. 56 3.9 Principal component analysis of functional groups associated with management system at four ranches in Chihuahua, Mexico in 2005. 57

x

LIST OF ABBREVIATIONS AND ACRONYMS

AU. Animal Unit

AUM Animal Unit Month

AUY. Animal Unit Year

ANPP-N. Above Ground Net Primary Production Nitrogen

CETES. Certificados de la Tesorería de la Federación (Mexico).

CONACYT. . Consejo Nacional de Ciencia Y Tecnología

CG Continuous Grazing COTECOCA Comisión Técnico Consultiva Para la determinación de los

Coeficientes de Agostadero cwt. hundred weight (per 100 pounds)

DM Dry matter.

FIRA. Fideicomiso Instituido en Relación a la Agricultura

GLM General Linear Model

ha hectare.

HILF High Intensity Low Frequency

HRM. Holistic Resource Management

INIFAP. Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias

Km . kilometers

ROT Rotation grazing System

SDG. Short–Duration Grazing

SL Season-Long

1

CHAPTER I

INTRODUCTION

Natural resources have been affected by human use, and vegetation is

one of the components most disturbed by this activity. The introduction of

domesticated animals in America, as well as in other places worldwide, has

replaced the grazing impact that native wildlife had for centuries on natural

vegetation. Many plant species had adapted to grazing by native animals

because they evolved together; however, plants are susceptible to domestic

grazing, and whole plant communities have been changed or replaced by other

communities because of this new grazing pressure (Stoddart et al., 1975).

Destructive livestock grazing in the western US occurred in the late 1800s

and early 1900s; however, it was largely arrested by WW II, when more intensive

management practices were applied to the majority of rangelands (Pieper, 1999).

This situation was aggravated with the invention and use of barbed wire.

Barbed-wire fences helped confine free-roaming animals to a specific piece of

land. Variable grazing rates by native herbivores were replaced by years of

season-long heavy grazing by livestock beginning in the late 1800s (Miller et al.,

1999).

Grazing animals affect plants both directly and indirectly. Direct effects of

grazing are those associated with alterations of physiology and morphology

resulting from defoliation and trampling. Grazing also influences plant

2

performance indirectly by altering the microclimate, the soil properties, and the

plant’s competitive interactions. Over time, the combined direct and indirect

effects of grazing on plant growth and reproduction become manifest in plant

population dynamics (Archer and Smeins, 1991).

Livestock grazing has played a role in decreasing the amount of fuel for

wildfires, altering nutrient distribution, acting to create patchiness at landscape

levels for many animal species, and disrupting cryptogamic crusts.

Nevertheless, domestic livestock grazing at conservative levels seems to be

sustainable (Pieper, 1999). As previously stated, many rangeland communities

were subjected to grazing, and therefore, the effect of grazing is an integral part

of the ecosystem. The discontinuation of grazing on rangelands has often been

based on the belief that decreasing or removing livestock will solve any existing

rangeland problem and rapidly return these lands to near pristine condition

(Vallentine, 2001). However, removing all livestock grazing would not return

rangelands to a pristine condition. In many cases the changes would be subtle,

and in the long run, they might even be negative in terms of biodiversity and

other desirable characteristics (Pieper, 1999).

Even under protection from large herbivores, vegetation is dynamic and

fluctuates in response to other controlling factors such as climate. The effect of

grazing by domestic livestock is variable. It is extremely difficult to generalize

because of differences in climate, resistance of various species to grazing,

3

stocking levels, composition of vegetation, grazing season, and many other

factors.

Despite the current development of sophisticated analytical techniques,

separation of grazing impact from climatic impact remains difficult (Holecheck,

1998).

1.1 Justification

For many decades, continuous grazing was practiced by ranchers in the

Western US. Because of this practice, detrimental effects on range condition

were observed in many areas in North America. Continuous grazing has often

been criticized as being detrimental to vegetation; however, the major cause of

deterioration has commonly been heavy grazing and/or poor distribution of

grazing (Vallentine, 2001).

This situation of decreasing range condition resulted in an early attempt at

grazing methods development. The primary objective of most grazing

management practices is to maximize livestock production per unit area of

rangeland, while maintaining a sustainable forage resource (Heitschmidt and

Walker, 1983). The inclusion of grazing deferment and rest were the first

practices implemented as grazing methods, which allowed vegetation recovery.

Rotational stocking methods have been recommended as a way to

enhance vegetation, livestock, and wildlife production. Theoretically, benefits

from rotational stocking results from control of selective grazing (Taylor et al.,

4

1997). Historically, an array of special grazing techniques has been collectively

referred to as “grazing systems.” These techniques vary from simple to complex,

and are available to further fine tune the management of grazing. “Special

grazing technique” is a generic term employed to include both grazing methods

and grazing systems. A grazing system is defined as a specialization of grazing

management based on rotating grazing animals among two or more grazing land

units (paddocks), while defining systematically recurring periods of grazing and

non-grazing. A grazing system will generally include one or more grazing

methods in addition to rotating grazing (Vallentine, 2001).

One innovative way to implement range management was promoted by

Allan Savory in Zimbabwe, Central Africa, in 1960. Inspired by the grazing habits

of wild animals in his home country, Savory developed a theory regarding the

way domestic animals could be managed to improve both animal and vegetation

performance. This new grazing management philosophy was named Holistic

Resource Management (HRM). One of the tools that include the HRM is the

Short-Duration grazing (SDG), which consist in the division of pasture in a large

number of paddocks, in order to rotate the livestock through all pastures, the

rotation is more rapid during growing season and slower during the mature stage

and dormancy, the length of grazing and rest depend on the number of

paddocks.

During the1980s, HRM resulted in controversial discussions because the

principles on which it was based are unusual, and to a certain degree, they

5

contradict many of the traditional range management guidelines. Much was

published regarding the evaluation of HRM on soil, vegetation, animal response,

and so on. The majority of these evaluations concur that HRM or SDG, which it is

also termed, instead of improving the animal, soil and vegetation measurements,

produces a detrimental effect on the measurements evaluated. The most

negative results obtained were observed in arid and semiarid environments. The

predominant vegetation under these situations is more fragile and sensitive to

mismanagement compared with more humid conditions. Most adverse effects

found were related to soil infiltration rate caused by soil compaction and

decrease in individual animal performance resulting from an increase in carrying

capacity.

Despite the adverse results obtained in most studies where HRM was

evaluated, some philosophical principles on which it is based are quite

interesting, mainly those that encourage the range manager to maintain a

frequent monitoring of soil, vegetation, and animal conditions. The establishment

of annual, monthly, and daily plans that may be redirected at any time depending

on monitoring results, is not a common practice in the majority of the grazing

system programs. However, the most interesting aspect of HRM is that some

ranchers, no matter what they expected in terms of vegetation response to

increased carrying capacity, perceive benefits in other aspects. For example,

they now practice a more opportunistic destocking during forage shortages.

Moreover, they are now more aware of the detrimental effect of

6

overgrazing and its negative effect on range condition. This effect increases

during drought periods such as those experienced in State of Chihuahua during

the past 14 years. Some ranchers who initiated the use of HRM were forced to

destock the ranches and use lower stocking rates because of the severe drought.

Nonetheless, because they invested a large amount of money in infrastructure,

some of them still practiced the HRM, but at lower stocking rates.

Many studies conducted by other people to evaluate the SDG lasted two

or three years, some were monitored for five or six years, but only few were

conducted for ten or more years. Determination of vegetation changes through

the implementation of range management practices is a process that takes time,

particularly when great climatic variation occurs. For this is the reason, one

objective of this study was to evaluate vegetation changes on some ranges that

have been managed under the HRM for more than a decade.

1.2 Objectives

To examine vegetation changes on private properties after 12 years.

To measure vegetation changes on private ranches that practiced Short-

Duration grazing compared with those that utilized Continuous grazing.

7

CHAPTER II

LITERATURE REVIEW

Barbour et al., (1989) described grasslands as herbaceous communities

dominated by graminoides (grasses, sedges, and rushes) but with forbs (non-

graminoid herbs) present and sometimes seasonally dominant. Trees are absent

except for local sites, such as along water courses or among rock outcrops.

Grasslands are dominated by annual grasses, perennial bunch grasses, or

perennial sod-forming grasses. Annuals are most abundant on dry, overgrazed,

or disturbed sites. Annual warm-season types germinate in spring or summer

and complete a much shorter life cycle in a matter of weeks, rather than months.

They do not reproduce vegetatively with runners or rhizomes. Six-week grama

(Bouteloua barbata, in the desert grassland), is such an annual.

Perennial bunch grasses, such as purple blue grama (Bouteloua gracilis)

produce tillers, and the continuation of that process for many years result in a

large clump a decimeter or more in diameter. Bunch grasses alone do not

generally produce a community with 100% cover, the spaces between clumps

can be seasonally filled by forbs and other grasses. Perennial sod-forming

grasses, such as big bluestem (Andropogon gerardii) in the tall-grass prairie,

spread laterally by rhizomes. New shoots and roots arise from nodes on the

8

rhizomes in such number that a turf results. Top soil is thoroughly penetrated

and held together by the fibrous root system, and a continuous sward of shoots

covers the surface. Sod-formers are more resistant to grazing than bunch

grasses because they have so many more growing points. Some sod-formers

are less aggressive than others, producing only short rhizomes, and some

produce rhizomes only under certain environmental conditions (Barbour et al.,

1998).

Forbs are also an important component on many grasslands. Forbs are

nongrass-like plants with tap roots, generally broad leaves with netlike veins, and

solid non-jointed stems. Shrubs, which are a minor component of most

grasslands, have woody stems that branch near base, and long, coarse roots.

Stems remain alive during dormant periods, which is different than most grasses

and forbs, with which the above-ground parts die back to the crown during winter

or during the dry season (Holecheck et al.,1998). More specific descriptive

terminology will be provided in the appendix section.

2.1 Short Duration Grazing

Grazing is the process by which some animals acquire their food needs to

meet their intake and nutritional requirements. Grazing in most natural

ecosystems is as much as part of the system as is the need for forage by grazing

animals. Most native rangeland evolved under animals grazing plants and plants

tolerating grazing (Vallentine, 2001).

9

Although, not native to western rangelands, livestock function similarly to

native herbivores in that they harvest plants, defecate, urinate and are involved in

nutrient cycles. In addition, livestock compete with and complement other

herbivores in rangeland ecosystem, and they may stimulate primary production

or depress it (Pieper, 1999).

Grazing management involves the regulation of this consumptive process

by humans, primary through the manipulation of livestock, to meet specific,

predetermined production goals (Briske and Heistchmidt, 1991).

Since SDG emerged as a new way to handle grazing animals, and

because it sounded too good to be true, many researchers were prompted to

evaluate this new paradigm in grazing management under different regimens.

The responses of vegetation to the SDG use vary, and many times these

variations are associated with climatic conditions. Weather interacts with grazing

treatments, species, and the combined effects of other factors, indicating the

dominant effect of weather, particularly precipitation, on changes in herbaceous

basal area (Teague et al., 2004). Nevertheless, a major concern is the failure of

SDG, as well as other grazing systems at high stocking rates (Pitts and Bryant,

1987; Pieper and Heischmidt, 1988). Stocking rates have much greater potential

than grazing systems for altering frequency and intensity of defoliation and

subsequent changes in botanical composition of range plant communities (Hart

et al., 1993).

10

Many aspects of SDG have been evaluated, from soil characteristics

(Weltz and Wood, 1986; Chanasyk and Naeth, 1995; Weigel et al., 1990) to plant

defoliation (Aiken and Springer, 1998; Guillen et al., 1998; Taylor et al., 1997;

Pierson and Scarnecchia, 1987), animal diets (Ortega et al., 1997; Hirschfeld et

al., 1996; Taylor and Kothmann, 1990; Kirby et al.,1986; Nelson et al., 1989),

cattle nutrition (Olson et al., 1989; Pitts and Bryant, 1987; McCollum and Guillen,

1998), animal performance (Volesky et al., 1990; Aiken, 1998; Bertelsen et al.,

1993), vegetation response (Taylor et al., 1997, White et al., 1991; Guillen et al.,

1991; Palmer et al., 1990; Hart et al., 1993; Dormaar et al., 1989), and many

other more specific vegetation, animal, and soil characteristics.

Although every aspect is important when evaluating a grazing system, the

vegetation issue is probably of major concern because all other concepts are

directly or indirectly interrelated to vegetation. As established previously,

diminishing range condition was the trigger that initiated the development of the

first grazing strategies. Grazing systems have been developed as a means of

increasing rangeland productivity by increasing carrying capacity (Pitts and

Bryant, 1987), and SDG is purported to sustain higher stocking rates through

increased forage production and utilization compared with other grazing systems

(Savory, 1983).

Results found in literature regarding the SDG are quite interesting,

because they seem contradictory. However, the major concerns with SDG are

the large investments in infrastructure, high stocking rates utilized, and pasture

11

size. In addition, outcomes in vegetation aspects and animal performance are

varied and highly dependent on climatic condition and vegetation types.

In a study conducted by Dormaar et al. (1989), it was found that range

condition decreased when the stocking rate was increased two- to three-fold

above that recommended on a festuca grassland in western Canada. Over five

years, Ralphs et al. (1990) conducted an experiment near Sonora, Texas, where

four stocking rates were used to determine whether the standing crop could be

maintained with a graze length of 3 days and 51 days of rest. Ralphs et al.

(1990) found little change in frequency and composition of short-grasses, but

mid-grass frequency and composition both declined. This decline was greater for

the fall than in the growing season, and inversely proportional to stocking rate.

Taylor et al. (1997) continued the previously mentioned study five more years,

and found that the tendency was the same: curly-mesquite (Hilaria belangerii)

increased in all treatments, and decreased in the livestock exclosure. Sideoats

(Bouteloua curtipendula) and other mid-grasses decreased under all stocking

rate treatments and increased with livestock exclusion.

Continuous grazing is considered the benchmark when any grazing

system is evaluated, and SDG is not an exception. In many instances no

differences were found when SDG has been compared with continuous grazing,

and many times the performance of continuous grazing was superior (Angell,

1997; Bryant et al., 1989)

12

Research comparing rotational with continuous grazing has generally

concluded that the effects of rotational grazing per se on defoliation patterns are

weak or absent. However, research on rotational grazing systems has invariably

been carried out using small paddocks, usually less than 25 ha, and often less

than 5 ha. In addition, research areas are specially chosen to be as uniform as

possible. Both factors significantly decrease the variability that causes patch

selection and the associated deterioration in large paddocks (Norton, 1998). In a

study conducted in Vernon, Texas, where the size of the pastures used as

replications ranged from 1,295 to 2,131 ha, the conclusion was that when

summer growing conditions were favorable, rotational grazing treatment resulted

in greater increases of perennial herbaceous basal areas and a lower proportion

of bare ground than the continuously grazed treatment. Although, rotational

grazing did not prevent deterioration in basal areas and bare ground with the

series of four drought years, it decreased the rate of deterioration (Teague et al.,

2004).

Decreased pasture size and distance to water may be responsible for the

alleged benefits of intensive time-controlled rotation grazing systems.

Comparisons were made on cattle gains and activity, distance traveled, and

forage utilization on a time-controlled rotation system with eight, 24-ha pastures,

on two 24-ha pastures grazed continuously (season-long), and on one 207-ha

pasture grazed continuously, stocked at the same rates. Utilization on the 207-

ha pasture, but not on the 24-ha pasture, decreased with distance from water. At

13

distances greater than 3 km from water in the 207-ha pasture, utilization was

significantly less than on adjacent 24-ha pasture at distances of 1.0 to 1.6 km

from water. Cows on the 207-ha pasture traveled farther (6.1 km/day) than cows

on the 24-ha rotation pasture (4.2 km/day), which in turn traveled farther than

cows on the 24-ha continuously grazed pasture (3.2 km/day). Grazing system,

range site, slope, and weather had minimal effect on cattle activity patterns.

Intensive rotation grazing systems are unlikely to benefit animal performance

unless pasture size and distance to water are decreased (Hart et al., 1993).

The stocking rate on semi-permanent heavily grazed patches is much

greater than the intended stocking rate of the paddock as a whole (Kellner and

Bosch, 1992). This leads to a progressive deterioration characterized by

replacement of taller perennial by shorter perennial grasses, followed by annual

grasses, and finally bare ground (Teague et al., 2004).

The vegetation response of SDG and continuous grazing at the same

stocking rates were similar in a tallgrass prairie (Guillen et al.,1998). Similarly,

after a four-year evaluation, Angell (1997) found no difference between high

stocked SDG and continuous grazing in crested wheatgrass tiller density.

However, they found that Wyoming sagebrush densities increased under high

SDG, but not under low stocking, and that SDG was similar to continuous

grazing.

Declining grassland productivity is a major concern in southern temperate

Australia. Continuous grazing is thought to be a primary contributor to this

14

decline, which is associated with the loss of perennial grasses. Dowling et al.

(2005) reported a comparison between continuous grazing and time-controlled

grazing with sheep and cattle using a paired-paddock design at 5 locations.

Throughout the sites there were a few consistent differences between

management treatments. Basal cover was greater on the time-controlled grazing

than continuous for most of the experimental period at three sites, but the initial

values were also higher (Dowling et al., 2005).

The practice of continuous grazing using low animal density in a

tobosagrass [Hilaria mutica (Buckl.) Benth.] rangeland in the northern

Chihuahuan Desert resulted in non-uniform forage utilization (Senock et al.,

1993). Stocking smaller tobosa rangeland paddocks with high numbers of cattle

for short periods of time may facilitate more uniform forage utilization. Two

grazing periods in each of two consecutive years were monitored to investigate

the frequency with which tobosa tillers were defoliated and the intensity of

defoliation (change in height) in relation to grazing pressure under high-density

seasonal rotational and low-density seasonal continuous grazing. Percentage of

tillers defoliated in the rotational treatment was always greater than 75%, and

always less than 30% in the continuous treatment. The probability that a tiller

would be grazed at least once in the rotational treatment was more than twice as

great as in the continuous treatment; however, within the rotational treatment,

the probability of multiple grazing events (greater than or equal to 2) of an

individual tiller was less than the probability of a tiller being grazed only once. In

15

general, high-density rotation grazing promoted more uniform forage utilization of

tobosa than low-density continuous grazing (Senock et al., 1993).

In a 6-year study conducted by Biondini and Manske (1996) the effects of

a twice-over rotation grazing system (ROT) and a season-long grazing system

(SL) were conducted to compare the effects with long-term grazing exclosure

(NG) in relation to: 1) species composition and basal cover; 2) above ground

net primary production (ANPP) and above ground N uptake (ANNP-N); 3) rates

of litter and root decomposition and N release; 4) soil N mineralization and

immobilization; 5) above ground C and N flow; and 6) grazing intensity (GI) and

animal performance. Species composition was more responsive to grazing than

were C and N flows. The differences in this case were found between grazed

and non-grazed treatments, but not between the two grazing treatments . No

broad patterns of change were detected in total plant basal cover as a result of

grazing patterns or drought. Changes in species composition were highly

dependent on range site. The most consistent pattern involved Bouteloua

gracilis, which had higher relative cover in the grazed treatments than in the non-

grazed treatments.

Results from this study indicated that in the grasslands of western North

Dakota: 1) the recommended stocking rate may be too conservative; 2) rotation

grazing may allow for higher stocking rates than season-long grazing without a

major effect on animal performance; 3) rainfall is more important than grazing or

grazing systems in the control of the ecosystem-level variables measured ; 4)

16

species composition is affected by drought and grazing (but not by grazing

systems), but the responses are highly dependent on range site; and 5) drought

and grazing tend to increase the relative composition of warm-season grasses

and forbs (Biondini and Manske, 1996).

From 1989 to 1993, Cassels et al. (1995) evaluated a grazing system and

stocking rate effect on forage standing crop of tall grass prairies in north-central

Oklahoma. Pastures were dominated by big bluestem [Andropogon gerardii

Vitman], little bluestem [Schizachyrium scoparium (Michx.) Nash], indiangrass

[Sorghastrum nutans (L.) Nash], and switchgrass [Panicum virgatum L.].

Rotation units were arranged with either a short duration rotation or continuous

grazing system and stocking rates ranging from 127 kg animal live weight/ha to

222 kg live weight/ha. Yearling steers grazed the units from late April to late

September. Herbage standing crop was sampled in July and September. Total,

live and dead standing crops did not differ significantly between the 2 grazing

systems in July. Total standing crop was significantly higher in the rotation units

in September (3,600 vs. 3,020 kg/ha). Dead standing crop was also greater in

the rotation units in September (1,950 vs. 1,570 kg/ha, P<0.05). The authors

suggested that the difference in standing crop between systems was due, in part,

to decreased forage intake by the livestock. Grazing system did not interact with

either stocking rate or year. Stocking rate had significant effects on total live and

dead standing crops at both sample dates. Higher standing crop at the end of

the grazing season in the rotation units would mean greater soil protection,

17

suggesting a lower effect on plant vigor. However, if the higher standing crop

was a result of lower forage intake, one would expect livestock weight gains to

decline. The assumption of a decrease in forage intake mentioned above is

questionable based on results found by Hirschfeld et al. (1996) and Soltero

(1987), who found that the forage intake by livestock grazing native grasslands

was higher under SDG than under continuous grazing.

2.2 Vegetation Changes

Allen-Diaz and Bartolome (1998), critiqued the classical succession

theory, which is still widely applied, which suggests that rangeland systems are

best described as predictable linear sequences of plant communities,

sequentially changing in an orderly response to control variables such as

grazing, fire, precipitation, and competition. But the development of models for

nonlinear, nonequilibrium plant community dynamics as an alternative; like the

State Transition proposed by Westoby et al. (1989), were plant communities may

change from discrete states and a set of discrete transitions between the states,

instead of follow a single continuum.

Moreover, Buttolph and Coppock (2004) mentioned that management

recommendations intended to decrease rangeland degradation and increase

livestock productivity often assume equilibrium conditions, wherein vegetation

and herbivore dynamics are tightly coupled and that recent research in Africa,

18

Asia, and North America, however, suggests that the dynamics of some arid

systems are driven more by precipitation, a non-equilibrium factor.

Ellis and Swift (1988), stated that plant production and composition in

many arid ecosystems depend more on climate than on herbivory. Nevertheless,

high stocking rates increase the effect of adverse weather conditions such as

severe droughts, and exert an additional detrimental effect on more desirable,

less defoliation-resistant species.

2.2.1 Cover

Continuous and reversible vegetation dynamics prevail within stable

vegetation states. Discontinuous and nonreversible dynamics occur when

thresholds are surpassed and one stable state replaces another (Briske et al.,

2005). Heavy grazing often results in a dramatic decrease of plant diversity,

vegetation cover, primary production (Fensham, 1998), and other soil aspects.

When degradation occurs as a result of intensive herbivory, Kraaij and

Milton (2006) stated that, it initially affects plant population demography. Once

this is initiated, diversity and productivity start to decline. Thereafter, a reduction

in perennial plant cover facilitates the establishment of ephemeral and weedy

species, which ultimately ends with the loss of vegetation cover. When

vegetation communities have been highly abused through heavy and prolonged

stocking rates and grazing use, the resiliency of those communities is difficult to

perform. The change and damage caused to vegetation is such that the return to

19

pristine vegetation is practically impossible, and a new vegetation assemblage

takes place. As was pointed out by Westoby et al. (1989) when he described the

mechanisms that produce the complex ecosystem communities’ dynamics.

In a grazing experiment conducted by Zhao et al. (2005) during 5 years in

a sandy rangeland in Inner Mongolia, continuous heavy grazing resulted in a

considerable decrease in vegetation cover and canopy height. Vegetation cover

in the heavy grazing plot was 58.6% less than that of the no grazing plot the first

year and 88% lower the fifth year. The vegetation cover increased slightly over

the study period in the light grazing and moderate grazing plots.

Range condition decreased under SDG system in a fescue grassland

(Dormaar et al.,1989) from 50 to 39%, whereas the range condition increased

within a grazing exclosure from 51.6 to 56.2%, during a 5-year period.

Graminoids increased from 58.1 to 65.7% within the exclosure, whereas the

grazed areas values changed from 64.4 to 65.7%. Fescue was a desirable

species that decreased under grazing treatment (1.3 to 0.7%); however, it

increased when the grass was excluded from grazing (1.6 to 6.0%). Other less

desirable species such as Carex, Koeleria, Bouteloua, and Poa, increased in

both treatments, but were slightly higher under the SDG system (Dormaar et

al.,1989).

Differences in plant species abundances in response to cattle grazing and

protection were measured at 15 sites in productive, semi-natural Mediterranean

grasslands in Israel by Noy-Meir et al. (1989). Perennial species with long

20

growing seasons increased somewhat more frequently under grazing protection,

and their total cover was greater in protected grassland. Grazing response was

significantly associated with growth form: increases under grazing protection

were mostly tall erect plants; increases under grazing treatment were mostly

small prostrated or rosette plants; and plants with intermediate responses were

mostly erect plants of medium height. Ungrazed grassland was dominated (60 to

80% cover) by tall perennial and tall annual grasses. Tall and medium legumes

were also prominent (15 to 30% cover). Under light to moderate grazing their

coverage decreased (35 to 50%) to the benefit of a wide range of growth form

and families. Under heavy grazing, tall perennial and tall annual plants

combined, covered 20 to 35 %, with two species accounting for the greatest

percent. One grazing resistant and one unpalatable plant, and small, prostrated,

annual rosette crucifers and thistles remained abundant.

2.2.2 Forage production

Some speculation regarding the herbivory optimization hypothesis

suggested that grassland may show an increase in productivity due to the

grazing process (McNaughton and Bardget, 1979). Nonetheless results have

been varied and contradictory, and even no responses have been reported.

Frank et al. (2002) reported a 21% increase in the above annual net primary

productivity due to grazing in a grassland, whereas Milchunas and Lauenroth

(1993) found a decrease in the above ground production.

21

Results reported by Taylor et al. (1993) of the effects of SDG and high-

intensity, low-frequency grazing systems showed that ANPP (grass + forbs)

increased for both grazing treatments in 4 years. Total ANPP varied significantly

among years but not between grazing systems. Total grass production averaged

128 g/m2 for the SDG treatment and 154 g/m2 for the HILF. Therefore, Taylor et

al. (1993) rejected the hypothesis that grazing systems increase ANPP.

In an experiment conducted by Zhao et al. (2005) in a sandy rangeland in

Mongolia, the standing crop biomass decreased significantly with increased

grazing intensity. The standing crop biomass decreased slightly but not

significantly with grazing time in both the heavy and moderate grazing

treatments. Conversely, it increased significantly with grazing time in the light

grazing treatment. The non-grazing treatment increased from early to mid-term

and showed a decreased trend thereafter. These authors assumed that this

might be due mainly to litter accumulation, which restricted plant growth.

Regarding the effects of grazing exclosure, Walker (1989) cited by West (1993),

mentioned that ungulate grazing is an important process in many rangeland

ecosystems. If grazing is excluded, biodiversity may increase in the short term

but decrease long-term because the system itself changes, and in the future, the

rangeland may be less able to withstand other disturbances such as drought and

fire. West et al. (1984), advised that if manager expectations of pathways and

time scales for vegetation recovery following a disturbance were unfounded, then

much time and potential rangeland productivity could be lost waiting for changes

22

that may never or very slowly materialize. In a study conducted by West et al.,

(1984) in the Tintic valley in west central Utah, the total standing crop did not

increase following 13 years of rest from livestock grazing. The average standing

crop from 1963-64 (grazed) to that of 1980-81 (ungrazed) was compared.

Authors emphasized the fact that the lack of change was even more

dramatic because the data from 1954-64 represent the residual herbage

following grazing during May-June, and the precipitation during 1980 was the

highest of the entire sequence. Nevertheless, herbage was considerably less

than the average (226 kg/ha) during the 1956-64 period. The standing crop of

many perennial grasses decreased over the 13 years of rest. In contrast,

cheatgrass apparently increased during the rest period.

In 1982, Dormaar et al. (1989) established a SDG system on 972 ha in a

fescue grassland at Fort McCleod, Alberta, Canada, that consisted of 17

pastures. Stocking rates varied from 3 to 2.3 AUM/ha over the five-year study.

Forage production fluctuated from 570 kg/ha in 1983, then decreased to

approximately 340 kg/ha in 1984 to 85, increasing again in 1986 to 784 kg/ha.

Forage utilization averaged 83% on the entire period.

Two grazing studies were conducted by Pitts and Bryant (1987), in which

continuous grazing and SDG were compared. The stocking rates used were

similar at the beginning, but in the second year, stocking rate was increased to

twice the continuous stocking rate in SDG, and in the third year, decreased to 1.5

times the continuous stocking rate. Standing crop was low on both CG and SDG

23

during the first 2 years of the study because of low rainfall. Greater standing

crop on SDG than CG in Year 2 was attributed to two relatively unpalatable

forage species. In the last two years of the trial, when adequate rainfall occurred,

forage availability was less under the SDG regimen. Changes in standing crop of

different grass species occurred during the 4-year study, but changes were

similar for both CG and SDG.

Stocking rate seems to be the most important factor that drives forage

availability; however, climatic conditions, mainly frequency and occurrence of

rainfall, are dominant in forage production fluctuation. Milchunas and Lauenroth

(1993) found a trend for decreased above ground production with grazing,

suggesting that the results at any given locality were influenced by moisture

availability and the evolutionary history of grazing.

2.2.3 Density.

The effects of grazing on changes in species composition of plant

communities have been extensively discussed in the literature. Cyclic changes

in plants densities throughout several years have been reported by many

researchers. However, the direct effect of grazing and climatic influences is often

confounded, making it difficulty to distinguish between them.

In 1956, 2 areas of mixed grassland and oak woodland at the Hopland

Research Extension Center of the University of California were fenced to exclude

sheep. The variation in density of perennial grasses through time among

24

grassland transects was striking. The overall pattern of change showed a

decrease by 1979, with a return to original density by 1991. In several plots, non-

native annuals dominated by 1979. By 2000, perennial grass density was

greater than in 1979, but still lower than 1959. For example, the dominant

species purple needlegrass was less abundant in 2000 (≈1.2 plants/m2) than in

1958 (≈1.8 plants/m2). After more than 40 years without livestock grazing, the

density of native perennial grasses was lower in open grassland than when

transects were established, but considerably greater than in 1979 (≈0.8 pl/m2)

(Merenlender et al., 2001).

Landsberg et al. (2002) conducted a study of native plant communities in

an arid rangeland region of South Australia to explore how rangeland grazing

affects native plant diversity at local and regional scales. Six transects were

spread across a large region, four transects were established within a

commercial sheep-grazed paddock, and two transects were established outside

in similar land that had never been developed for pastoralism. Transects were

established at 1, 4 ,7, and 10 km from the nearest water point in the paddock,

and the outside (at more than 10 km distance) on undeveloped sites. Nearly 200

species were recorded, but distribution was patchy, with more than 30% of

species present at less than 105 of sites. At a regional level, pastoral

development had a predominantly negative effect on the abundance of species.

Sixteen species were less abundant within paddocks than in areas that

had never been developed, and only one species was more abundant. The local

25

trend was more positive than the regional trend, in that significantly more species

showed trends of increasing abundance with increasing proximity to watering

points and associated grazing activities. Based on these results, Landsberg et

al. (2002) concluded that pastoral development enhanced richness of plant

species at local scales (by providing opportunity for more species to establish),

but that it had the potential to decrease richness at a regional scale by removing

the most grazing-sensitive species from the regional species pool.

In the northern Chihuahuan desert, Nash et al. (1999) evaluated the

response of annual plant communities to grazing. They concluded that

disturbance by grazing livestock resulted in only small changes in annual plant

communities and that it was very different from the effects of intensive livestock

grazing on perennial vegetation. This might be the reason why in most degraded

perennial grass communities, the remnant vegetation after a severe drought or

prolonged overgrazing is mostly annual grasses and forbs.

Conclusions;

• Grazing is a process that has played an important role in the

grassland development over the time.

• Overgrazing practiced during late 1800s and early 1900s resulted

in a severe deterioration of vegetation in many grasslands in

western United States and Northern Mexico.

26

• Continuous grazing was the most commonly grazing method

utilized, and overgrazing of most desirable species and a non

uniform utilization was a common denominator under this grazing

scheme.

• More grazing systems were developed in an attempt to improve

ranges condition. Rotational grazing systems became a very

popular strategy in grazing management to solve the overgrazing

problem.

• Short-Duration grazing was very popular in the 1980s based on the

premise of improved grazing distribution, improved soil infiltration,

and a two to three-fold increase in carrying capacity, among others

benefits.

• Results on SDG studies are contradictory, but most of them did not

observe any advantages compared with continuous grazing;

however, the major concerns were related to the use of high

stocking rates that were not sustainable and the fact that no soil

improvement was achieved.

• In general, most of the literature agreed that stocking rates were

more determinant on vegetation response than grazing system

effects, particularly when environmental conditions were adverse.

27

CHAPTER III

VEGETATION CHANGES AFTER 12 YEARS IN FOUR

PRIVATE RANCHES UNDER SHORT-DURATION AND

CONTINUOUS GRAZING IN CHIHUAHUA, MEXICO

3.1 Introduction

The cattle industry in northern Mexico has been identified for many years

because of extensive grazing. Erratic rainfall and other weather conditions limit

land use to grazing in most of the region. In the State of Chihuahua, rangelands

suitable for grazing have been well identified. According to COTECOCA (1978),

eighteen native and one introduced vegetation types within sixty-four rangeland

sites were recognized, and estimated stocking rates ranged from 8.5 to 60.0

ha/AUY.

Because of overgrazing and desertification processes, carrying capacity in

many ranches in Mexico has actually decreased (Manzano and Navar, 2000). In

addition, property size has decreased through time because of both population

increase and increased production costs (Molinar et al., 1998). Under this

situation, in the late 1980s and early 1990s, some ranchers, searching for

alternatives that could improve or ameliorate the critical condition of their ranch

enterprises, thought that SDG would be the solution to their crisis. Stocking rate

increases and range condition improvement were the most attractive aspect of

this practice. Short duration grazing is a system that enables more rigid control

28

of animal distribution with the use of numerous smaller pastures, thereby

concentrating livestock and permitting time-controlled grazing. It has been

proposed that short duration grazing will allow conventional stocking rates to

double or triple, regardless of range condition at the time of implementation

(Dormaar et al.,1989; Savory, 1983). However, is well known that most changes

in vegetation that have occurred in native rangelands that have been related to

grazing effects through years, specifically where heavy, continuous grazing has

been practiced, takes year to reversed.

Over time, many people were disappointed by the SDG results and

returned to their traditional CG. Others still believe in the benefits of this

particular grazing system and continue practicing and managing their ranches

using SDG. Based on these observations, the present study was proposed to;

1) evaluate vegetation changes on private ranches as a result of different grazing

management after 12 years, and 2) Measure the differences in vegetation cover,

forage production, and density on four ranches in Chihuahua, Mexico two

managed under SDG and two under CG.

3.2 Material and Methods

3.2.1 Study Sites

Around 1990, several ranches implemented the HRM in Northern Mexico,

as illustrated in Figure 3.1. Among other reasons for implementing this system,

HRM was strongly promoted by various private and public agencies as FIRA

29

from Banco de Mexico that organized several symposium and field days.

Vegetation on four of these properties in Chihuahua, Mexico were measured in

1993.

Figure 3.1. Location of Chihuahua State in Mexico.

Ranch 1

Ranch 1 was a family operated ranch, located approximately 340 km NW

of Chihuahua City at 30o 26’ 42’’ lat N and 108o 11’ 30’’ long W, at approximately

1,500 m above sea level. The long-term annual rainfall average was 370 mm,

mean annual temperature ranges between 16 to 18oC, with 200 frost-free days.

At this property, 9,731 ha were managed under HRM. Fifteen paddocks of

different sizes were established, ranging from 157 to 1,607 ha, as shown in

Figure 3.2.

Vegetation at this ranch was considered as mid-open grassland

(COTECOCA, 1978). Major vegetation species included desirable species such

as Bouteloua gracilis, B. eriopoda, B.hirsuta, B. curtipendula, and less desirable

Chihuahua City

30

species such as Digitaria californica, Setaria macrostachya, some species of

Aristida, and Lycurus phleoides. In 1993 the stocking rate was established at 7

ha/AUY. After 1994 to 2005, stocking rates were changed because of drought,

fluctuating as follow: 9, 11, 10, 11, 11, 15, 11, 11, 10, 10, 11, 16, and 15 ha/AU,

only cow/calf pairs were used.

Figure 3.2. Pasture distribution and vegetation type in Ranch 1.

Ranch 2

This ranch is located approximately 130 km NW Chihuahua City, between

29o 11’ 00’’ lat N and 106o 50’ 53’’ long W, at 2,000 m above sea level. Annual

long-term rainfall average was 440 mm with approximately 105 mm in the form of

snow. Mean temperature is 14 to 16oC, with 180 frost-free days. This rangeland

belongs to a larger area, but under this cell, only 2,868 ha were included and split

31

in four pastures (Figure 3.3), an average stocking rate of 6 ha/AUY was assigned

to this grazing unit.

Vegetation was described as a mid-open grassland in high valleys

(COTECOCA 1978). The characteristic species are Bouteloua gracilis,

Bouteloua hirsuta, Buchloe dactiloides, also, Setaria macrostachya, Bouteoua

curtipendula, Chloris latisquamea, Leptocloa dubia, Panicum obtusum, Panicun.

hallii, Lycurus phleoides, Aristida ternipes, Aristida. divaricata, Aristida orcuttiana,

Microchloa kunthii, and Leptoloma cognatum.

Figure 3.3. Pasture distribution and vegetation type in Ranch 2.

Ranch 3

This unit was located about 160 km north of Chihuahua City, between 29o

50’ 37’’ lat N and 106o 36’ 16’’ long W at 1,400 meters above sea level. Average

32

annual rainfall wass approximately 350 mm, with an annual mean temperature of

15 to 17 oC and 200 frost-free days. Approximately 1,531 ha were included

under the SDG. The area was divided in 16 equal size paddocks (Figure 3.4).

The initial stocking rate was approximately 12 ha /AUY, approximately 200 young

heifers of 250 kg that came from other ranch were allotted to these pastures in

January, and remained at this unit until December, when they were removed and

a new herd was brought the next year.

After 1999, all internal fences were removed, except one at the middle that

separates the pasture in two large paddocks. Thereafter, stocking rates were

Figure 3.4. Initial pasture distribution and vegetation type in Ranch 3.

decreased to 17 ha/AUY, and 40 female calves grazed 6 months (January

through June); followed by 65 nursing mature cows the next 6 months (July

33

through December), and the unit was split in two parts, with the same stocking

rate. Most common desirable species for this area included Bouteloua gracilis,

Bouteloua. hirsuta, Bouteloua chondrosoides, Bouteloua curtipendula, and

Buchloe dactiloides. Less-desirable species include; Bouteloua eriopoda,

Digitaria californica, Setaria macrostachya, Leptochloa dubia, Aristida pansa,

Aristida ternipes, Aristida. hamulosa, Aristida adscencionis, Aristida arizonica,

Lycurus phleoides, Eragrostis intermedia, Panicum obtusum, Hilaria mutica,

Eneapogon desvauxii. Invasive species were considered; Botriochloa barbinodis,

Botriochloa. saccharoides, Erioneuron pulchellum. Also several other plants

such; annual grasses, some annual forbs and also several toxic plants as;

Drymaria arenarioides, Solanum eleagnifolium, and Baileya multiradiata, and

shrubs species like Prosopis juliflora, Mimosa sp., Ephedra sp., Flourencia

cernua, and Larrea tridentate, were considered invaders as well.

Ranch 4

This private ranch is located 300 km NW Chihuahua City, between 30o 32’

28’’ lat N and 107o 33’ 16’’ long W, at 1,400 meters above sea level. Average

annual rainfall was 300 mm, with an average annual temperature of 16 to 18 oC

and a 210 frost-free days. Vegetation was classified as medium-tall shrubland

(COTECOCA 1978). Dominant species include Prosopis juliflora, and Fourencia

cernua, also Mimosa biuncifera, Koeberlina spinulosa, Ephedra trifurca, Opuntia

imbricata, Condalia spp, and Celtis pallida. The most important grasses were

34

Bouteloua eriopoda, Bouteloua trifida, Digitaria californica , Setaria macrostachya

Bouteloua gracilis, Lycurus phleoides, Aristida pansa, Aristida divaricata,

Botriochloa saccharoides, Hilaria mutica, Hilaria belangeri, and Scleropogon

brevifolius.

This grazing unit size was 2,600 ha, which included two grazing cells,

together forming a 13-paddock grazing unit (Figure 3.5). At the beginning of the

implementation of SDG, a stocking rate of 7 ha/AUY was assigned.

After several years of low rainfall, the internal paddocks were removed,

and a new stocking rate was initiated, with an average of 16 ha/AU. From 1993

to 2005 the stocking rates fluctuated as follow: 7, 7, 15, 16, 16, 18, 22, 21, 14,

14, 14, 14, and 23 ha/AUY. Initially cow/calf pairs were used, after 2001 only

stockers.

Figure 3.5. Initial pasture distribution and vegetation type in Ranch 4.

35

3.2.2 Management

Each ranch was managed by the owner or their land manager. Every

manager was trained in the HRM philosophy and/or had an advisor from the

HRM Center in Mexico. Researchers do not participate in the management of

these ranches. Personnel from the HRM Center argued that the needs of the

ranchers were different from that of technicians and researchers. Therefore, the

only research concern was to record vegetation changes on these ranches

through time.

Ranches 1 and 2 were managed under SDG for the entire period 1993-

2005, Ranches 3 and 4 started were under SDG from 1993-1998, but returned to

Continuous Grazing System (C) for the remaining 7 years 1998-2005

3.2.3 Sampling

The first vegetation sampling was conducted in Fall 1993, and the same

procedures were repeated in Fall 1994; and in late Fall 2005. Vegetation

variables evaluated were percentage of basal (herbaceous) and aerial (shrubs

and suffrutescents) cover, density (individuals/area), and forage production (kg

DM/ha). Two pastures on each ranch were randomly selected on which to

establish permanent transects. In each pasture a set of 12-m transects was

established at different distances from the center of the pastures or the source of

water. The distances among varied from 250 to 400 m depending of the shape

and the size of the pastures at each ranch.

36

3.2.4 Vegetation measurements

Permanent transects, 12-m long, were established in two pastures

(Canfield, 1941). The basal cover was measured using 12 m-long permanent

transects, plants were measured individually (Canfield, 1941), one end of each

transects was oriented toward the water source at the center of pastures and the

other to a reference point at the end of the pasture. Measurements were made

on the same transects in Fall 1993, 1994, and 2005. For grasses and

herbaceous plants, data collected were based on basal area, whereas for brush

and shrub-like plants, aerial coverage was recorded. The number of transects

varied among ranches, which occurred because not all transects established in

1993 were relocated in 2005, the number of transects surveyed varied from 9 to

10, except at one ranch, where all transects were located. Initially 18 transects

were located at each ranch but, some sticks were removed or missed, mainly by

the animals. In ranch 1 ten permanent transects were measured, in ranch 2

eighteen transects, in ranch 3 nine transects, and at ranch 4 nine transects were

relocated

To estimate grass forage production (kg DM/ha) a 0.25-m2 quadrats were

clipped (Cook and Stubbendieck, 1986). Four quadrats were randomly located

on each transect. Forage samples were clipped at approximately one inch above

soil surface, samples were oven dried until constant weight at 55 oC for 72 hours

37

to determine dry matter content. Twenty-four samples per pasture and 72

samples per ranch were collected.

To estimate grass and herbaceous vegetation density two 0.125-m2

quadrat were placed, one at each terminal end of each permanent transects.

Every individual plant within quadrat was counted. Most plants were identified to

species but, those that were not identified, a common name or any other

description was used to distinguish each species. Where shrubs occurred, a 3.0-

m diameter plot was located at each end of every permanent transect, to

estimate its density. To facilitate the vegetation analysis, the species were

divided into the following functional groups: shrubs, suffrutescents, perennial

grasses, annual grasses, perennial forbs, and annual forbs. Rainfall data were

collected from rainfall gauges located on each one of the ranches included in the

study.

3.2.5 Statistical Analyses

Perennial grass cover data were analyzed by analysis of variance with

repeated measurements (years) using the Proc Mixed procedure, Compound

symmetry was used as covariance structure, and basal cover from the initial year

was used as a covariate to adjust for antecedent conditions. The Shaphiro-Wilk

normality test was performed to evaluate the distribution of the data. LSMEANS

comparisons were made to asses the differences between the initial and final

perennial grasses basal cover distribution. To determine differences in forage

38

production, the Proc Mix procedure was used to run a Analysis of variance, with

repeated measurements, using initial survey as covariate (SAS/STAT, 2004). In

order to contrast the importance of functional groups as a descriptor of the

vegetation variation in the first year with the to the last year, using management

system as ordination value, a Principal components multivariate analysis was

done.

3.3 Results

3.3.1 Rainfall

The timing of rainfall occurrences was very similar at all locations.

However, ranches under SDG management received a larger amount of rain

than those under traditional management. The general pattern across sites

showed 4-5 years that were equal or above average annual rainfall, and 5 to 7

years of severe drought conditions during this 12-year period. However, after

1994, precipitation was above average for only one or two years. Ranch 4, had a

lower amount of precipitation during the entire 12-year period (Figure 3.6). In

general, weather conditions were considered as a severe drought during a

considerable period of time during the evaluation period.

3.3.2 Cover

Initial basal cover (1993) was greater (P=0.0004) in SDG (23.2 ± .9 %)

than in CG (3.3 ± 1%). Because the initial basal cover was different between

39

treatments, the initial condition was used as covariate.

Statistical difference was found between years of sampling (P=0.0001),

the basal cover was greater in 1994 (11.4 ± .6%) than in 2005 (6.6 ± .6%).

Ranch 1 (SDG) Ranch 2 (SDG)

0

200

400

600

800

90 92 93 94 95 96 97 98 99 00 01 02 03 04 05

Years

Mili

mite

rs

Annual Mean

0200400600800

90919293949596979899000102030405

YearsM

ilim

eter

s

Annual Mean

Ranch 3 (CG) Ranch 4 (CG)

0

200

400

600

90919293949596979899000102030405

Years

Mili

mite

rs

Annual Mean

0

100

200

300

95 96 97 98 99 00 01 02 03 04 05

Years

Mili

met

ers

annual mean

Figure 3.6: Rainfall patterns of four ranches under Short Duration (SDG) and Continuous (CG) grazing management in Chihuahua, Mexico.

40

Treatments by year interaction was detected (P≤ 0.0002). Statistical

difference (P=0.0001) was found in 1994 between treatments, SDG showed a

greater basal cover (16.5 ± 1.1%) than CG (6.3 ± 1.5%). However, in 2005,

there was not statistical (P = 0.51) difference, SDG had (5.8 ± 1.1%) basal cover

and CG system had (7.4 ± 1.5%). In general, basal cover of perennial grasses of

the ranches that used the SDG system declined. The highest percent was found

in 1994 (16.5%) and then it tended to decline toward 2005 (5.8%). Statistical

difference (P < 0.0001) in percentage of perennial grasses basal cover was

found among years in ranches managed with the SDG treatment (Table 3.1).

Table 3.1: Basal cover (%) (± SEM) of perennial grasses in four ranches under two different grazing systems in Chihuahua, Mexico.

*Covariate Mean in a row with different capital letters were different (P<.0001) Mean in a column with different lower case letter were different (P<.0001) Mean in a column with the same lower case letter were similar (P>.05)

Treatment

Year Short-Duration Continuous Overall Mean

1993* 23.2 ± 0.9A 3.3 ± 1B

1994 16.5 ± 1.1Aa 6.3 ± 1.5Ba 11.4 ± 0.64a

2005 5.8 ± 1.1Ab 7.4 ± 1.5 Aa 6.6 ± 0.6b

41

The perennial grasses basal cover was lower in ranches managed under

CG system than under SDG. Despite the initial basal cover being lower on

ranches under CG management (3.3%), the adjusted values showed a slight

tendency to increase in 1994 (6.3%), and a slight increase was observed later on

toward 2005 (7.4%), the magnitude of changes over years was not significant

(P = 0.36).

Perennial grasses accounted for the greatest basal cover (cm) among all

the functional groups in Ranch 1, followed by the annual forbs (Table 3.2)

Bluegrama (Bouteloua gracilis) was the species with the highest basal cover

length among all the perennial grasses. Threeawn (Aristida spp) and

tobosagrass (Hilaria mutica) also contributed to the cover of perennial grasses in

1993, but less than blue grama. An overall decrease in amount of cover close to

40% was observed in perennial grasses by 2005. Comparatively, cover

decrease was higher for threeawn and tobosagrass than for blue grama. All

functional groups showed a tendency to decrease from 1993 to 2005. Within

annual grasses, only two species accounted for the basal cover but, just one

Bouteloua spp. (9 cm/1200 cm) was important in 2005, along with two species of

perennial forbs, Sida procumbens and Solanum eleagnifolium 2 cm/1200 cm

each in 1993 but both disappeared in 1994 and 2005. Of the annual forbs,

Heteroteca spp (40 cm/1200 cm) was dominant in 1993, with two others

unidentified forbs showing minor participation. In 1994 only one species of a

legume species was recorded with a 1.1 cm/1200 cm the rest were too small and

42

Table 3.2: Basal (forbs and grasses) and aerial (shrubs and suffrutecents) cover (cm/1200cm) of species present in sampled transects,

categorized by functional groups in Ranch 1.

Year SPECIES 1993 1994 2005 SHRUBS Mimosa spp 3.2 Subtotal PERENNIAL GRASSES Bouteloua gracilis 213.7 177.0 104.2 Aristida adcensionis 45.1 21.9 0.9 Hilaria belangeri 6.7 4.3 2.0 Panicum spp 0.5 0.1 Hilaria mutica 17.1 17.2 Botrhiocloa barbinodis 0.9 2.2 Bouteloua curtipendula 9.3 10.6 11.1 Bouteloua hirsuta 11.1 14.1 3.9 Lycurus phleoides 9.4 13.8 1.9 Schizachirium spp. Mulhenbergia spp, 1.4 4.0 Bouteloua eriopoda Subtotal 313.3 263.0 128.1 ANNUAL GRASSES Aristida annual Chloris annual 0.4 Eragrostis annual 9.0 Bouteloua annual Subtotal 0.0 0 9.4 PERENNIAL FORBS Guillemina spp 0.9 Sida procumbens 1.9 Hoffmansegia spp. Solanum eleagnigolium 2.0 0.2 0.1 Dalea spp 0.6 Malva spp 0.3 Leguminose 0.5 Subtotal 5.4 0.5 0.6 ANNUAL FORBS Hairy forb 4.7 Heteroteca spp 40.2 Grindelia spp Compositae 0.4 1.2 Annual Forb 8.7 0.3 3.3 Argemone mexicana 0.2 Cyperacea 0.4 Tronadorcillo 0.2 Spharalcea spp 0.4 Ceniza 3.3 Paronichya spp

43

Table 3.2: Continued Species

Aphanosteohus spp 11.0 Gnaphalium canescens 3.0 Hypericum spp 2.3 Euphorbia spp 0.2 Leguminose 1.1 Cebollin Compositae 2 1.9 Subtotal 74.4 2.0 6.4

Cover is the average in 1200 cm transects.

two not previously reported annual forbs were found in 2005, but both were found

in a very low coverage.

Similar trends to Ranch 1 in cover length were observed for Ranch 2. A

general decreasing tendency in cover length in all categories from 1993 to 2005

was noticed. Within the perennial grasses functional group, again blue grama

accounted the highest basal coverage. Threeawn and wolftail (Lycurus

phleoides) contributed a lesser proportion compared with blue grama (Table 3.3).

In 1993, length of cover of the rest of herbaceous strata was very limited; among

annual grasses only one species of Eragrostis (0.7 cm/1200 cm) was barely

recorded. Within perennial forbs, four species with equal proportions were noted,

but total amount were small (7.7 cm/1200 cm). With respect to annual forbs, two

non-identified species accounted for the major amount of cover, but in low

quantities (4 and 9.5 cm/1200 cm). In 1994, a slight increase was observed in

perennial forbs cover: Dalea spp increased to 5 cm/ 1200 cm in cover, and two

new species showed up, Drymaria arenarioides and Zinnia spp., but, in a very

small amounts (3.2 and 1 cm/1200 cm respectively). Contribution to basal cover

44

Table 3.3: Basal (forbs and grasses) and aerial (shrubs and suffrutecents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 2. Year SPECIES 1993 1994 2005 SHRUBS Mimosa spp. 52.1 50.3 56.9 Condelia spp 3.3 Subotal 52.1 15.2 60.3 PERENNIAL GRASSES Bouteloua gracilis 178.2 153.7 76.5 Aristida spp 22.9 18.7 5.1 Lycurus phleoides 22.7 22.1 1.8 Microchloa kuntii 4.1 4.2 2.2 Mulhenbergia spp 2.5 2.9 0.67 Elyonurus barbiculmis 3.3 Schizachirium spp. 4.4 7.1 2.2 Bouteloua hirsute 8.6 1.7 0.2 Botriochloa barbinodis 0.0 Subtotal 243.5 213.6 88.8 ANNUAL GRASSES Eragrostis annual 0.7 0.7 Bouteloua annual 0.0 Panicum annual 0.3 Aristida annual 0.1 Chloris annual 0.0 Subotal 0.7 0.3 1.0 PERENNIAL FORBS Dalea spp. 1.7 5.0 0.1 Drymaria arenarioides 3.2 Yerbaniz 2.0 0.9 Guillemina spp 0.6 Zinnia spp 1.0 Perennial Forb 1.6 Croton spp 2.5 Subtotal 7.7 10.7 0.1 ANNUAL FORBS Red forb 4.0 0.8 0.2 Annual Forb 0.4 0.5 Hairy forb 0.2 Forb 2 2.3 Lepidium spp 1.4 Vigueria spp 6.1 Forb 3 0.1 Little strawberry 1.2 Cyperacea 0.1

45

Table 3.3: Continued Species Big forb 9.5 2.6 Star forb 0.9 0.3 Gnaphalium canescens 0.1 Composite 0.8 Eringium spp. 0.1 Grape weed 1.9 Subtotal 17.2 15.2 0.9

Cover length is the average in 1200 cm transects.

of perennial and annual forbs in 2005 was much less than in 1993 and 1994 or

they had disappeared. A new species of genus Bouteloua, Aristida, and Chloris

annual grasses were recorded but, only in traces.

Mimosa spp. was the only species that accounted for shrub aerial cover in

1993 (52 cm/1200 cm). In 2005, Condelia spp was also noted but in a small

amount (3.3 cm/ 1200 cm). Mimosa spp. coverage remained stable across time

with a slight decrease at the end (57 cm/ 1200 cm).

In Ranch 3, basal cover of perennial grasses performed differed from that

of Ranches 1 and 2, in that cover increased from 1993 through 2005. Lehmann

lovegrass (Eragrostis lehmanniana) and threeawn (Aristida spp.) were the

species with the greatest amount of coverage. Both species had similar values

in 1993; nevertheless, in 2005, Lehmann lovegrass increased more than two-fold

in the amount of cover, whereas threeawn decreased approximately 60% in its

basal cover length (Table 3.4). Blue grama also contributed to the coverage of

perennial grasses in this ranch in 1993, but only in small way, remaining

unchanged through 2005.

46

Table 3.4: Basal (forbs and grasses) and aerial (shrubs and suffrutescents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 3. Year SPECIES 1993 1994 2005 SHRUBS Acacia angustissima 3.8 0 1 Ephedra sp. 9.8 5.3 0 Prosopis sp. 69.8 61.1 70.7 Mimosa spp. 0.0 0.0 0.0 Condelia spp. Subtotal 83.3 66.4 71.7 SHRUBS-LIKE Menodora like 7.0 Xantocephalum sarotrae 1.8 Subtotal 8.8 0 0.0 PERENNIAL GRASSES Eragrostis lehmanniana 19.2 10.7 49.8 Bouteloua gracilis 8.3 4.7 8.7 Mulhenbergia porteri 1.3 Botrichloa barbinodis 3.8 Setaria macrostachya 2.4 5.6 Digitaria californica 0.8 0.6 3.1 Cenchrus incertus 0.7 Eneapogon desvauxii 0.3 0.2 Panicun obtusum 0.6 0.0 Aristida spp 16.4 10.4 6.3 Sporobolus airoides 0.8 Panicum halli Subotal 53.9 33.9 68.1 ANNUAL GRASSES Bouteloua curtipendula (annual) 0.1 Eragrostis annual 1.4 1.4 Aristida annual 15.2 2.2 Bouteloua annual 4.3 0.4 Panicum annual 6.7 0.6 Chloris annual 4.8 Mulhenbergia annual 0.8 Subtotal 33.2 2.8 2.0 PERENNIAL FORBS Sida procumbens 10.3 18.2 0.1 Legume 0.3 Calcomeca 0.1 Hoffmansegia spp 22.7 2.6 0.3 Forb perennial 6.3 Zinnia spp 6.9 1.0

47

Table 3.4: Continued Species Forb 2 Croton potsii 0.6 2.7 Coldenia spp Cassia spp 1.3 Solanum eleagnifolium 0.6 0.2 Subtotal 47.0 26.3 0.3 ANNUAL FORBS Evolvolus spp 7.4 3.9 0.3 Annual forb 1 0.2 Composite 0.6 Hairy forb Cotton forb 0.1 Curly forb 1.9 Amaranthus spp 1.1 Eringium spp. 0.3 Cebollin Subtotal 10.9 4.4 0.6

Coverage is the average in 1200 cm transects.

Perennial forbs accounted for the second largest amount of cover in 1993

of herbaceous functional groups at Ranch 3. Immediately below perennial

grasses; Hoffmansegia spp., was the species responsible for the major amount

of cover. In 2005, however, a dramatic decrease in coverage occurred in this

group of plants to the point that they were just barely recorded. The same pattern

occurred with annual grasses; some species of the Aristida genus were the most

common within this functional group, followed by Panicum, Bouteloua, and

Chloris.

Within annual forbs, Evolvolus spp., was the predominant plant at Ranch

3. Shrubs constituted part of the plant (aerial) coverage at this ranch; however,

their contribution was limited. The aerial cover length of shrubs varied from 83

cm out of 1200 in 1993 to 71 cm/ 1200cm in 2005. Mesquite Prosopis spp. was

48

the predominant species in this group. Other species, Acacia angustissima and

Ephedra spp. were also recorded in 1993, but they were not important in 2005.

In fact, one species (Ephedra spp.) was not recorded the last year.

Vegetation characteristics in Ranch 4 were quite different from the other

three ranches. Perennial grasses were not the dominant group at this ranch. Its

basal cover length was only 27 cm out of 1200 cm in 1993, and it almost

disappeared in 2005 (1.9 cm/ 1200 cm).

Arizona cottontop (Digitaria californica) and Plains bristlegrass (Setaria

macrostachya) were the most significant species in the perennial grasses

functional group with 8.1 and 5.6 cm/1200 cm respectively (Table 3.5). Broom

snakeweed (Gutierreza sarotrae), a very common short-lived half-shrub in the

Chihuahuan desert landscape that is highly influenced by winter moisture, was

an important species at Ranch 4. In 1993, this species accounted 202 cm/1200

cm out of 1200, the highest cover length (aerial); however, it is not surprising that

it decreased to 31.2 cm/1200 cm in 2005.

Although basal cover of perennial forbs was greatest among all the

herbaceous groups in 1993, even more than perennial grasses, the cover length

noted for this group is considered small (40 mm/1200 cm). In 2005, the cover

determined for this group was even smaller than the first year.

Among the annual grasses two Bouteloua and one Panicum species

were recorded in a very small amounts the first year, accounting only 9.7

cm/1200 cm over all annual grasses, and disappeared by 2005.

49

Table 3.5: Basal (forbs and grasses) and aerial (shrubs and sufrutecents) cover (cm/1200 cm) of species present in sampled transects, categorized by functional groups in Ranch 4. Year SPECIES 1993 1994 2005 SHRUBS Budleja scordioides Parthenium incanum 32.2 31.1 Ephedra sp. 11.1 Prosopis sp. 72.3 95.2 76.2 Mimosa spp 6.1 Flourencia cernua 29.3 21.9 54.0 Atriplex spp 0.6 Condalia spp Subtotal 140.0 148.8 141.3 SUFFRUTECENTS Xantocephalum sarotrae 202.6 94.2 31.2 Agave spp 3.6 Subtotal 202.6 94.2 34.8 PERENNIAL GRASSES Lycurus phleoides 0.7 Bouteloua gracilis 2.4 3.3 0.2 Bouteloua eriopoda 0.8 0.7 0.8 Botrichloa barbinodis 0.3 Setaria macrostachya 5.6 1.1 0.4 Digitaria californica 8.1 2.3 Erioneuron pulchellum 1.0 Eneapogon desvauxii 1.6 Aristida adscencionis 3.6 Aristida spp 3.7 0.7 0.4 Subotal 27.7 8.1 1.9 ANNUAL GRASSES Eragrostis annual 3.0 Aristida annual 0.6 Bouteloua barbata 1.4 Panicum annual 2.0 Chloris annual 0.3 Bouteloua aristirioides 2.9 Subtotal 9.7 0.0 0.6 PERENNIAL FORBS Sida procumbens 5.0 0.8 Legume 0.7 Solanum eleagnifolium 0.2 Hoffmansegia spp 0.1 0.2 Verbena spp Zinnia spp 2.3 0.4

50

Table 3.5: Continued Species Legume2 0.3 Dichondria argentea 1.1 0.2 5.4 Guillemina spp 0.4 Legume 3 27.7 Legume 4 0.7 Cassia spp 0.3 1.7 Subtotal 38.0 2.1 8.0 ANNUAL FORBS Evolvolus spp 0.3 Annual forb 1 0.2 White forb Ddysodia spp 0.9 Tronadorcillo Cabezuela Vigueria spp 8.8 Hybiscus spp Amaranthus spp Red forb 0.8 White flower forb Big forb 0.3 Salsola spp 0.1 Subtotal 0.9 0.0 10.6

Cover is the average in 1200 cm length transects.

Within perennial forbs only Sida procumbens and a none identified

legume species were important in 1993, and disappeared later on. Dichondra

argentea was the only perennial forb species present in 2005. Annual forbs were

almost absent in 1993, and were present in only a very small amount in 2005;

Vigueria spp. was the plant with the larger coverage in 2005.

Shrub aerial coverage remained steady over the years, with 140 and 141

cm out of 1200 cm for 1993 and 2005, respectively; including mesquite and

tarbush (Flourencia cernua), and a browse species mariola (Parthenium spp.) as

the major contributors in this group.

51

In Ranches 1 and 2 (SDG), perennial grasses were the functional group

with the largest percentage of coverage. Annual forbs were another group that

contributed to basal coverage during 1993. In 2005, however, the amount of its

coverage was less than 1%. In these two SDG ranches, shrubs were present

only at Ranch 2. Aerial cover of shrubs was relatively small, fluctuating from 4%

in 1993 to 5% in 2005 (Table 3.6).

Vegetation cover in Ranch 3 followed a different trend than that in Ranch

4. In Ranch 3, the largest herbaceous strata coverage was formed by the

perennial grasses and perennial forbs. Although they were the major proportion,

it was small. Basal cover in 1993 was 4.5 and 3.5%, whereas in 2005, it was 5.6

and 0.03% for both perennial grasses and forbs, respectively. Aerial cover of

shrubs was only 7% in 1993 and 6% in 2005, so their contribution was

considered not relevant, taking in account that the value correspond to canopy

cover.

In Ranch 4, the basal cover of herbaceous plants was very limited.

Perennial forbs had the greatest value, but it barely passed 3% in 1993. In 2005

no herbaceous group was larger than 1%. Shrubs-like plants showed the largest

aerial cover in 1993 (16%); however, they declined drastically in 2005 (2.9%),

whereas the shrubs functional group remained more stable, accounting for 12%

through time.

Initial basal cover was greater in ranches managed under SDG system

than in the traditional CG system (P=.0004); however, the difference in basal

52

Table 3.6: Basal cover (%) by functional groups in four ranches under Short Duration (SDG) and Continuous (CG) grazing management in Chihuahua, Mex. (2006). Ranch/ Basal cover (%) Functional Group 1993 1994 2005 Ranch1 (SDG) Perennial Grasses 26.1±1.9 21.92±2 10.68±2.8 Annual Grass 0.00 0.00 0.78±0.3 Perennial Forbs 0.45±0.2 0.04±0.1 0.05±0.1 Annual Forbs 6.20±2.3 0.17± 0.53±1.4 Ranch 2 (SDG) Shrubs 4.34±2.5 4.19±2.3 5.02±1.6 Perennial Grasses 20.29±1.2 17.80±1.3 7.40±1.5 Annual Grasses 0.06±.03 0.02±.02 0.09±0.01 Perennial Forbs 0.64±0.2 0.89±0.3 0.01±0.16 Annual Forbs 1.44±0.8 1.27±0.7 0.08±0.3 Ranch 3 (CG) Shrubs 6.94±3.4 5.54±2.8 5.97±3.2 Shrubs-like 0.73±0.6 0.00 0.00 Perennial Grasses 4.49±1.2 2.90±0.8 5.68±0.9 Annual Grasses 2.77±0.7 0.23±0.6 0.17±0.5 Perennial Forbs 3.92±1 2.19±0.9 0.03±0.9 Annual Forbs 0.91±0.4 0.37±0.2 0.05±0.2 Ranch 4 (CG) Shrubs 11.67±3.5 12.40±3.6 11.78±3.5 Shrubs-like 16.88±3.2 7.85±3.1 2.90±2.9 Perennial Grasses 2.31±.5 0.68±0.4 0.16±0.4 Annual Grasses 0.81±0.2 0.00 0.05±0.9 Perennial Forbs 3.17±1.6 0.18±1.1 0.67±0.4 Annual Forbs 0.07±0.1 0.00 0.88±0.4

53

cover was smaller in 2005 that at the beginning of the study (Figure 3.7). In

general the trend for perennial grass basal cover was to decrease in the four

ranches independently of the treatment, except in Ranch 3 (continuous), where

an increase in basal cover was observed by 2005.

26.0+1.9

21.9+2

10.6+2.8

20.3+1.2

17.7+2

7.3+1.54.5+1.2 2.9+.885.6+.96

2.3+.5 0.6+.44 0.16+.40

5

10

15

20

25

30

1993 1994 2005

Ranch 1 SD Ranch 2 SD Ranch 3 C Ranch 4 C

Figure 3.7: Perennial Grasses Basal Cover (%) in four ranches, under Short- Duration (SDG) or Continuous (CG) grazing management in Chihuahua, Mexico.

According to the results of the principal component (PC) analysis using

grazing system as the ordination value, in 1993 PC 1 explained 42% of total

variation (Table 3.7). Perennial grasses basal cover accounted as the most

important predictors of vegetation variation in ranches managed under SD

Year

Bas

al C

over

(%)

54

grazing system (-0.5638), and annual forbs basal cover seemed to the second

major source of variation (-0.2778) as shown in Figure 3.8. With regard to

ranches that used traditional CG management as grazing system, annual

grasses (0.4232) and perennial forbs (0.4341) basal cover were the most

important variables describing the vegetation variation in this grazing system

(PC1; Figure 3.8). Principal Component 2 (PC2) explained only 16.9% of the

Table 3.7: Eigenvectors for the significant components resulting from a principal component analysis conducted in 1993 and 2005 for vegetation changes in ranches with different grazing systems. Eigenvectors 1993 2005 Variable PC1 PC2 PC1 PC2 Shrubs 0.3159 -0.4898 0.321 -0.5879Shrubs-like 0.3701 -0.2872 0.5769 0.2963Perennial Grasses -0.5638 0.0138 -0.543 0.2733Annual Grasses 0.4232 0.5505 0.1016 -0.3498Perennial Forbs 0.4341 0.3868 0.5084 0.3791Annual Forbs -0.2787 0.4739 0.019 0.475 Component Variation explained Cumulative variation

PC1 0.4216 0.4216

PC2 0.169

0.5906

PC1 0.3072 0.3072

PC2 0.19350.5006

variation, annual grasses (0.5505) and shrubs (-0.4898) were the variables that

produced the highest variation in both grazing systems.

In 2005, only 30% of total variation was attributable to PC1; perennial

grass basal cover (-0.543) not only was the most important variable describing

the variation of vegetation in ranches managed under SDG system, but also

55

accounted for a smaller amount for variation in the ranches with CG

management. Nevertheless, suffrutescents aerial cover (0.5769) was the

variable that caused the major variation in continuous grazing (Figure 3.8).

Principal Component 2 accounted for 19% of total variation. Annual forbs

cover (0.475), and shrubs aerial cover (-0.5879) were important in both SDG and

CG management.

In 2005, the variable that had the major influence in PC2 in SDG managed

ranches was annual forbs basal cover; however, both the shrubs aerial cover

and annual grass basal cover were responsible for the greatest variation in the

two ranches that used the traditional CG system management.

3.3.3 Forage Production

Ranches managed under SDG had a greater (P = 0.006) forage

production (634 ± 56 kg DM/ha) than those managed under CG grazing (339 ±

57 kg DM/ha). Also, statistical difference was found (P=0.08) between initial

forage production of treatments. In 1993 the forage production was greater in

ranches managed under SDG (1098 ± 232 kg DM/ha) than in those under CG

grazing (795 ± 232 kg DM/ha). Because the difference in initial forage production

in the treatments, the forage production was adjusted by the initial condition. In

general, forage production was slightly greater in 1994 (521 ± 50 kg DM/ha) than

in 2005 (453±50 kg DM/ha); however, no statistical difference (P = 0.28) among

years of sampling was found, Table 3.8.

56

Prin2 ‚ 4 ˆ ‚ 2 ‚ ‚ A.Grasses(.55) ‚ ‚ ‚ 3 ˆ ‚ ‚ ‚ ‚ ‚ 1 ‚ 2 ˆ ‚ ‚ ‚ 2 ‚ ‚ 1 2 ‚ 2 1 ˆ 2 ‚ ‚ 1 ‚ 1 1 2 ‚ 1 ‚ 1 2 ‚ 2 2 0 ˆ P.Grasses(-.563) 1 1 2 P.Forbs(.434) A.Grasses(.423) ‚ 11 1 1 1 ‚ 111111 1 ‚ 2 ‚ 1 2 ‚ 2 ‚ -1 ˆ 1 2 ‚ ‚ ‚ 2 2 ‚ 2 2 ‚ 1** -2 ˆ ‚ Shrubs(-.489) Šƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒˆƒƒ -3 -2 -1 0 1 2 3 4 Prin1 NOTE: 4 obs hidden.

Figure 3.8: Principal components analysis of functional groups associated with management system as an ordination value at four ranches in Chihuahua, Mex. in 1993. ** 1 Short-Duration 2 Continuous

57

Prin2 ‚ 3 ˆ 2 2 ‚ ‚ ‚ A.Forbs(.475) ‚ ‚ ‚ 2 ˆ ‚ ‚ ‚ ‚ ‚ ‚ 1 ˆ 1 ‚1 1 ‚ 1 1 1 2 ‚ 1 1 1 2 ‚ 1 ‚ 2 1 2 ‚ 2112 2 0 ˆP.Grasses(-.543) 111 1 Suffrutescents(-.576) ‚ 1 11 ‚ 1 2 ‚ 1 2 ‚ 2 ‚ 1 ‚ 2 -1 ˆ ‚ ‚ 1 ‚ ‚ 2 ‚ ‚ 2 -2 ˆ ‚ ‚ 1 ‚ 1 ‚ 2 ** ‚ ‚ Shrubs(-.587) -3 ˆ ‚ ƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒ -2 -1 0 1 2 3 4 5 Prin1 NOTE: 4 obs hidden. Figure 3.9: Principal components analysis of functional groups associated with management system as an ordination value in at four ranches in Chihuahua, Mex. in 2005. ** 1 Shorth-Duration 2 Continuous

58

A treatment by year interaction was found (P=0.001), the forage

production in ranches managed under SDG had a lower production in 1994 (815

± 70 kg DM/ha) than in 2005 (453 ± 70 kg Dm/ha), whereas the CG managed

ranches showed an opposite trend, with a lower production obtained in 1994

(228 ± 70 kg Dm/ha) than in 2005 (451 ± 72 kg DM/ha).

In 1994, statistical difference (P = 0.0002) in forage production was found

between SDG and CG grazing systems, whereas in 2005, no statistical

significant difference was found (P = 0.98).

Table 3.8: Forage production (kg DM/ha) in ranches managed under Short- Duration (SDG) or Continuous (C) grazing systems in Chihuahua, Mexico.

Treatments

Year Short-Duration Continuous Average***

1993*† 1098±232a 795±232b

1994 815±70Aa 228±70Ab 521±50A

2005 453±70Ba 451±72Ba 452±50A

Mean** 634±56a 339±57b

*Initial (1993) means with different lower case letters within a row are statistically different(P=0.08) **Treatments means with different lower case letters within a row are statistically different(P=.05) ***Years average with same capital letter are statistically similar (P=0.28) Means within treatments with different capital letter within same column are statistically similar (P≤0.03) Means within year with different lower case letter same row are statistically different (P=0.002) Means within years with same lower case letter in same row are statistically similar (P=0.98) †Covariate

59

The fact that a treatment by year interaction was detected suggests that

the variation in forage production was a result of variation in rainfall patterns over

the period of study or other factor, and cannot be attributed only to the difference

of grazing management effect.

3.3.4 Density

In general, a decreasing pattern was observed from the beginning to the

end in plant density at all four ranches. Blue grama was the most abundant

species in Ranches 1 and 2, increasing from 1993 to 1994, but decreasing

drastically by 2005. The same pattern as blue grama was shown by threeawn

and side oats in Ranch 1 and 2. Microchloa kuntii, the second most abundant

species presented a linear trend, decreasing from 1993 to 2005. In Ranch 3,

threeawn was the most abundant species in 1993, followed by Lehmann

lovegrass. By 2005, threeawn almost disappeared, whereas density of Lehmann

grass increased two-fold.

In Ranch 4, some species of annual grasses; Panicum spp, Erafrostis

spp, and Bouteloua aristiroides, along with threeawn were the most abundant

species in 1993. However, in 2005, the density of all species was very low, with

some species even disappearing. There was a huge population of broom snake

weed in 1993, but in 2005 a tremendous reduction in plant density of broom

snakeweed was observed (see table 4.16 in Appendix).

60

3.4 Discussion.

Perennial grasses basal cover (%) was the most consistent and reliable

variable on which to base the criteria to evaluate the vegetational changes.

Teague (2004) mentioned that when monitoring sustainable use, basal area are

between the most sensitive indicator. Nash (2006) concluded that changes in

annual communities in the Chihuahuan Desert response to livestock grazing

intensities differ from that on perennial vegetation. Taylor (1997) recommended

the monitoring of grazing use on preferred plants. In a study conducted by White

et al. (1991) perennial grasses showed the most dependable cover data, other

forbs species were present in rather small quantities in all pastures; but did not

exhibit a consistent trend in pastures.

Perennial grasses basal cover in SDG was different from the CG system

at the beginning of the study (P = 0.0004), but not at the end of the period of

evaluation (P = 0.51). Dowling et al. (2005) found no consistent differences in

response in perennial grasses basal cover percentage in 5 sites evaluated in

grassland components in southeastern Australia. Basal cover was greater on

time controlling grazing management compared with continuous grazing, but

initial values was also greater, except that they did not find management by

time interaction, as was noted in the present study..

All four ranches showed a decrease in basal cover toward the last year

evaluated, except for Ranch 3. At this ranch, the presence of an exotic species

(Lehmann lovegrass) produced a change in the observed pattern for the other

61

species, showing an increase in basal cover in last year of evaluation. Lehmann

lovegrass is a very aggressive, introduced species that has been invading open

spaces in desert rangelands, often replacing native species. Smith and Schmutz

(1975) noted this situation in a desert grassland range in Arizona. Additionally,

McClaran and Anable (1992) mentioned that livestock grazing is not necessary

for Lehmann lovegrass to spread, but that its relative abundance was greater at

higher grazing intensities.

Perennial grasses basal cover in ranches managed under SDG showed a

greater decline (P = 0.0001) than with traditionally managed ranches were basal

cover of perennial grasses remained stable (P = 0.36). This response could be

attributed to the fact that higher stocking rates were used under the rotational

systems compared with the traditional CG system, although coverage was

greater since the beginning, and remained greater in ranches managed under

SDG system no statistical difference was found (P = 0.98) on the last year of

evaluation (2005). Nonetheless, the magnitude of the decrease in perennial

grasses basal cover was greater in SDG than in traditionally managed CG

ranches.

The average stocking rates used in SDG systems were greater than those

used in CG managed ranches; however, in the present study, the range condition

of traditionally managed ranches was poorer than in the SDG ranches,

particularly in Ranch 4. This situation can be seen in Table 4.6. Initial perennial

grasses basal cover was 4.5 and 2.6% in Ranches 3 and 4 respectively,

62

compared with 26 and 20 % in Ranches 1 and 2, respectively. Although, the

higher stocking rate used in SDG system seemed to have more effect on

vegetation than grazing system.

A considerable amount of literature supports the statement that stocking

rate influences vegetational changes more than the grazing system (Heady,

1961; Van Poolen and Lacey, (1979); Angell, (1997); Pitts and Bryant, (1987);

Guillen et al., (1998)).

The major species in ranches under SDG management was blue grama,

which is widely recognized because of its grazing and drought resistance (Fair et

al., 2001). However, its basal coverage decreased in these four ranches.

Perhaps the grazing intensity and the magnitude of drought were so intense, that

this species was not capable of maintaining its cover size and/or recuperating in

a short period of time. This perception is supported by the decrease observed in

density of blue grama in the quadrats sampled at the same places.

An analysis in global range environments was conducted by Milchunas

and Lauenroth (1993). They concluded that changes in species composition

were primarily a function of ANNP, and the evolutionary history of grazing on the

site, with level of consumption being third in importance. These three variables

explained >50% of the variance in the species response of grasslands or

grasslands-plus-shrublands to grazing, even though methods of measurement or

grazing systems varied among studies. Sensitivities of changes in dominant

species were greater to varying ecosystem-environmental variables than to

63

varying grazing variables, from low to high values. The response of shrublands

was different from that of grasslands, both in terms of species composition and

the dominant species. Species dissimilarity of grazed vs. ungrazed shrubland

was less than for grassland, and increases in dominants in grazed areas were 9

times more likely in shrublands compared with grasslands Guillen and Sims

(2006) found that basal cover of grass species did not respond to the stocking

rate in a single direction in a 20-year study, but exhibited continuous variation

according to rainfall patterns. The effect was more evident during dry years.

With regard to environmental factors that interact with vegetation changes;

Vetter (2005) noted that the current paradigms in ecology and range

management describing the equilibrium models that support the importance of

biotic feedback such as density-dependent regulation of livestock population and

the feedback of livestock density on vegetation composition, cover and

productivity, and management are centered on carrying capacity, stocking rates,

and range condition assessment. Conversely, the non-equilibrium paradigm

suggests that rangeland systems are driven by stochastic abiotic factors,

essentially rainfall, resulting in a highly variable primary production, and that the

livestock population is rarely in equilibrium with its fluctuating resource base.

The decrease in perennial grasses basal cover was caused mainly by two

factors: high stocking rates and the low amount rainfall that occurred in several

years within the study period, regardless of grazing system. This finding agrees

with the conclusions expressed by Herbel and Anderson (1959) after they

64

evaluated the response of true prairie vegetation on major Flint Hills range sites

to different grazing treatments. They compared heavy, moderate, and light

season-long stocking, and deferred-rotation at a moderate stocking rate. The

major factors influencing changes in plant composition were the stocking rates

and the variation in weather conditions from abundant moisture before mid 1951

to severe drought that remained through 1955.

The amount of rainfall received over the study period varied considerably

(Figure 3.6), but the most remarkable aspect was the number of years in which

the precipitation was less than 80% of the annual average; precipitation less

than 75% is considered to reflect severe drought conditions. An extreme

situation in vegetation condition occurred in Ranch 4, where even before the

evaluation period, the drought was critical and becoming worse over time.

Despite a decrease in stocking rate in some years, the adverse rainfall conditions

that prevailed across the time (Figure 3.6) aggravated the situation.

Biondini et al. (1998) did not find differences among non-grazing,

moderate grazing, and heavy grazing treatments, in a Poa pratensis dominant

species, mixed-grass prairie in North Dakota in terms or absolute basal cover

and absolute density; however, they found a significant positive correlation

(r2=0.77) with annual precipitation. Their conclusion about the mixed-grass

prairie was that climatic variation, in particular droughts, control major trends in

plant species composition and production, with grazing playing a secondary role.

65

O’connor (1994), also reported similar conclusions, and agreed that

rainfall variability had more influence on species abundance than grazing

intensity.

The forage fluctuation observed in all ranches could be considered more a

result of rainfall than a grazing effect. The trend observed in forage production

was similar to perennial grasses basal cover. Both are closely influenced by

rainfall conditions, but forage production is probably more sensitive to

environmental changes than is basal grass cover.

In 2005, the greatest and the least forage production values were

measured at the ranches with traditional management. In Ranch 4, the range

condition was becoming worse because of the impact of grazing and adverse

environmental conditions that prevailed during the entire study period. Forage

production was limited to only 100 kg DM/ha, whereas in Ranch 3, the presence

of Lehmann lovegrass resulted in a greater response in forage production in

2005 than was noted for Ranch 4.

In general, forage production was low, and the small amount of

precipitation during some years over the study period was the cause of this

response. Nonetheless, the last year (2005) was at or slightly above average.

Vegetation did not respond and thereby result in a substantial increase in

forage production, mainly due to the decrease in perennial vegetation basal

cover, as well as a reduction in plant density. Unfortunately, the lack of

intermediate samples taken between 1994 and 2005 did not allow the

66

establishment of a more clear tendency through time. Beck and McNeeley

(1991) reported a close relationship (r2= 0.53) between plant biomass and

precipitation in the Chihuahuan desert rangeland over 20 years. In a study

conducted by Heitschmidt et al. (1987), with two different stocking densities in a

rotational grazing system, no differences were found in ANNP between the

treatments, but variation among years was evident. In general ANNP was

greater in the paddocks with highest stocking density. Total standing crop had

two peaks, one of them occurred because of an increase in annual broomweed

herbage production.

Van Poolen and Lacey (1979) compiled results from reliable studies

regarding comparison of grazing systems and stocking rates separately. They

reported that rotational grazing versus continuous grazing increased herbage

production by 13%. While decreasing from heavy to moderate stocking rates,

the increment in herbage production fluctuated around 35% compared with 28%

with a change from a moderate to a light stocking rate.

Socio-economic factors.

The changes in vegetation observed in the ranches evaluated were not

merely the result of mismanagement of rangelands by the owners. The origin of

the problem is more complex than simply an overstocking practice. A brief

67

analysis will be done to explain some of socio-economic factors that contributed

to exacerbating the rangeland deterioration in the ranches evaluated.

Historically, the uncertainty in land ownership has contributed to

overstocking or overgrazing of rangelands. The landlord tried to make more

profits from the land because the threat of loosing part of their land by the

government expropriation from ranchers that owned a larger amount of land than

that allowed by law, which started in the 1930s and continued through the early

1990s, and was latent in many instances. The lack of security in land ownership

contributed to exploitative land use (Molinar et al., 1998). All people that faced

this situation tried to run as many cattle as possible, as they wanted to obtain as

much value from the land as they could before they lost it. Under these

circumstances, the land degradation was aggravated every year.

The financial crash of the Mexican economy in 1994 and the drought that

started the same year and lasted for approximately 10 years also influenced

landowners choices and the concomitant vegetative results..

During the late 1980s and early 1990s, an aggressive program from the

Central Mexican Government promoted the implementation of an innovative

grazing system (Savory system or SDG), with the aim of improving the efficiency

of the ranch enterprises nationwide. Doubling carrying capacity was the magnet

which drew the government and landowners to the program. Large amounts of

investment were needed to implement the system; however, the low interest

rates offered by financial institutions at that time to promote the program resulted

68

in several ranches implementing the system. The expectancy of some ranchers

of doubling the ranch carrying capacity in a short period of time, and

subsequently increasing profits, would allow them to easily overcome the debt

situation and could be able to afford the debt contracted.

A common practice for many years was to obtain credits early in the year

to finance most of the ranch variable costs and to repay them the end of the year

after calf crop was sold. This practice worked for many years because the

interest rate fluctuation was more stable, and the constant slide of Mexican peso

allowed the debt on the contracted loans to be paid because the Mexican calf

market is strongly tied to prices in dollars. This situation seemed to put them in

even better shape. Unfortunately after 1994, the Mexican economy passed a

tremendous crisis, and sometimes the interest rates rose above 100%, making in

many instances the debts of many ranchers non-payable.

An important aspect in ranches’ economy is cattle price. Feeder prices at

1994 were below $100.00/cwt until 1999 (180 kg average live weight), and as

low as $66.00/cwt in 1996, decreasing the gross income tremendously. In

addition to the economic situation, the environmental conditions faced by the

rancher were the worst in many years. The precipitation pattern in the 4 ranches

evaluated during the 1994 to 2005 period showed 5 to 7 years out of 12 with

severe drought.

Holecheck (1998) pointed out that climatic and financial conditions are

among the greatest risks in range livestock production. In arid and semiarid

69

environments, recurrent droughts are well recognized and expected. Smart et al.

(2005) cited 14 times out of 95 years that a severe drought occurred in the Great

Plains. Holecheck (1996) made reference of 3 out of 10 years are characterized

by less than 75% of precipitation in the growing season in several parts in New

Mexico. Many Mexican ranchers in Chihuahua as well as some of the New

Mexico land owners (Holecheck, 1996) were forced to liquidate more than 50%

of their cattle inventories due to lack of forage with giveaway prices for cattle

after Fall 1994.

Cattle sold during droughts are often discounted in the marketplace

because of increased supply, decreased demand, poor livestock condition, and

untimely marketing. Market value of livestock may be depressed below book

value or balance sheet value, which causes problems with net-worth statement

and potentially with lenders (Dunn et al., 2005).

Profitability of ranches in Chihuahua State is critical, and it varies among

the geographical locations in the state. Martinez-Nevarez (2002) evaluated 154

ranches in the state of Chihuahua. The average size was 4500 ha, with a base

of 185 mother cows. Most ranches showed losses in their operations, and the

benefit/cost ratio was 0.95 on average, the investment return was -5.4%, the

break even calf crop selling price was $1.00 in 158 kg average weight. A 20-year

financial projection suggested that the average net present value was close to -

$290,000.00 and the internal rate of return was 2.79 points lower than the

Mexican discount rate (CETES).

70

Thus, the critical financial situation, the prolonged drought, the previous

range condition, and the declining cattle market, collectively contributed to an

overuse of the limited forage resources, thereby hastening the decline in basal

cover of the perennial grasses and the deterioration in the range condition. In

some cases, these changes allowed for an increase in less desirable species or

an increasing bare soil.

Shoop and McIlvain (1971) suggested that an extra supplementation or

feed complement can be profitable until the plant and soil resources are badly

damaged, or until a series of drought years combined with low or dropping cattle

prices “terminate” the business or put it in a subsistence level. Thus, energy

supplementation was performed by most of the ranchers for many years, until the

point of no return, when the extended drought plus the overstocked ranges finally

showed up in the most vulnerable resource, the vegetation. This ultimately

resulted in a decrease in basal coverage, forage production, density of plants,

and, of course, land deterioration.

71

CHAPTER V

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

This study evaluated the effects of grazing systems on vegetation

changes in private ranches. Short Duration Grazing was compared with

traditional Continuous Grazing system.

The question implicit in the initial objectives was which is the best grazing

management practice? This question was posed with the aim that it would lead

to identification of more efficient and sustainable grazing management practices

to enable decision making that would be more suitable and operating under

different environmental conditions. In the present study, basal and aerial cover,

forage production, and plant densities of present vegetation were surveyed, while

rainfall was recorded. This took place at four ranches managed under either

short-duration or continuous grazing systems in Chihuahua, Mexico.

Initial condition (1993) in basal cover was different between ranches under

SDG and CG. The perennial basal cover was greater in SDG ranches than in CG

managed ranches

Higher decline tendency was observed in SDG managed ranches

compared with CG, however, after the values were adjusted due the difference in

initial condition, no difference was found between treatments in the last year of

the evaluation period (2005).

72

Forage production showed a similar performance to that observed in basal

cover. The initial forage production (1993) was greater in SDG than in CG

system managed ranches. Also a decline in forage production was observed in

both treatment but, the magnitude of the difference was greater in SDG

compared with CG. No difference in forage production was found at the end of

the evaluation period (2005).

The decline in basal cover and forage production were definitely

influenced by the low precipitation received during the evaluation period. Even

though, the forage production could be considered more sensitive to climatic

conditions.

The greatest decline observed in basal cover and forage production in

SDG compared to CG, is most probably in response to the higher stocking rates

used in SDG.

The presence of lehmann lovegrass in one of the ranches under CG

affected the response of the vegetation in this treatment.

Grazing systems effects were not separable from the environmental

conditions and high stocking effects during the time of study. This finding agrees

with works found in the literature review .

The financial and market conditions indirectly increased the pressure on

rangelands. Given the economic situation prevailed during study period,

ranchers were unable to decrease stocking rates because cows rather than

73

range are visualized as the product. This resulted in more attention being

focused on retaining large number of animals instead of increasing vegetation.

As Shoop and McIIvan (1971) cited previously said, the extended drought

plus the overstocked ranges finally showed up in the most vulnerable resource,

the vegetation.

5.2 Management Implications

The implementation of SDG does not provide any vegetation improvement

compared with traditional CG when high stocking rates are utilized in SDG.

However, the vegetation response could be improved, however, at lower stocking

rates.

The use of high stocking rates when an undesirable, unpalatable, and

aggressive grass species is present, such as Lehmann lovegrass, will favor the

spread out of this species; aggressive species will increase its coverage and

density, often replacing highly desirable species. This displacing process would

likely occur under any grazing system when high stocking rates are used.

The amount of money required to construct a large number of

intermediate fences is substantial. Thus, return on these investments will require

many years.

In ranches that actually have the infrastructure established and are

continuing under the SD grazing system, a reduction in stocking rates is

imperative. Otherwise, the deterioration of vegetation deterioration will continue

74

with each passing year. Lowered income by a decrease in the number of grazing

cattle will be compensated by a reduction in supplemental feed during dry

seasons, which most ranches in Chihuahua experience so far for 5 to 6 months

every year. This would also decrease the risk under the recurrent periods of

severe droughts. Moreover, an improvement in production variables is expected

under moderate stocking rates, as well as an improvement in range condition. In

years with more favorable environmental conditions, producers could purchase

stocker cattle or raise their own stocker cattle as an alternative to maintaining a

larger cow herd, considering that stocker cattle are more readily transformed into

cash.

When a year at or above average rainfall show up after a severe drought ,

a decrease in stocking rate might prevent the continued reduction in perennial

grasses basal cover and forage production; however, when the deterioration is

too severe, the potential vegetation response is very limited, no matter he

grazing system used.

5.3 Recommendations for further studies.

In this study, the changes in basal and aerial cover, forage production,

and plant density were surveyed after 12 years in four private ranches under two

different grazing systems, SDG or CG. As in many other studies, the high

stocking rates used in SDG and the drought conditions minimized the effects of

the grazing system.

75

Many questions that were noy answered from this study remain and could

be integrated to future researches.

The most important aspects to evaluate in the implementation of future

studies on SDG could be considered:

The use of moderate stocking rates

The performance of grazing animals to low stocking rates

The economic analysis of the grazing system

The inclusion of more number and more homogeneous grazing units

Increase the number of year of evaluation

Use more than one herd in the grazing unit

Increase in grazing period in the growing season to 7-10 days

The use of moderate or proper stocking rates has not been tested under

SDG. Many researches initially agreed that HRM principles make sense, except

for the idea that carrying capacity could be increased two-fold and that hoof

action is beneficial.

Test the use of moderate stocking rates in combination with more than

one herd at a time, thereby splitting the stocking densities among more pastures,

mainly at times when grasses are more nutritious could be important.

In addition, the use of high stocking densities was justified under SDG

because it would promote soil water infiltration, but this was not proved in many

instances. Density problem could be avoided by spreading the animals into more

76

paddocks instead of grazing just one a time. Splitting herds should be more

desirable mainly during early growing stage by allowing the animals to have

access to more nutritional forage at the same time, decreasing grazing pressure

by other animals. Rotating the herds every 7 to 10 days at the same time with

multiple herds might be more suitable than every 2 to 3 days with a single herd.

In arid environments, it is not uncommon that vegetation completes a

cycle in a very short period of time depending on the rainfall pattern. Thus, at the

end of rotation after 28 to 30 days, the vegetation on the first pastures grazed will

be mature. At later stages when vegetation is more mature, the rotation could be

conducted as the system originally proposed, allowing the perennial plants

accumulate enough energy to form the buds that will promote the tillering next

year, ensuring persistence of perennial vegetation, mainly perennial grasses.

77

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85

APPENDIX

86

APPENDIX A

VEGETATION COVER (CM), DENSITY (PLANTS/M2), AND

FORAGE PRODUCTION (KG DM/HA)TABLES OF

SAMPLES TAKEN BY YEAR

BY RANCH

87

Table 4.1 List of species sampled in Fall 1993:Cover (cm/1200cm) lengthRanch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10

SPECIESSHRUBSMimosa spp 0 0 0 0 0 0 32 0 0 0Subtotal 0 0 0 0 0 0 32 0 0 0PERENNIAL GRASSESBouteloua gracilis 254 349 261 73 100 122 85 256 285 352Aristida adcensionis 64 5 6 0 14 66 92 32 86 86Hilaria belangeri 0 0 0 45 0 0 22 0 0 0Panicum sppHilaria mutica 0 0 0 171 0 0 0 0 0 0Botrhiocloa barbinodis 0 0 0 6 3 0 0 0 0 0Bouteloua curtipendula 0 0 0 0 70 9 0 0 14 0Bouteloua hirsuta 0 0 0 0 111 0 0 0 0 0Lycurus phleoides 0 0 0 0 0 40 0 32 22 0Schizachirium spp.Mulhenbergia spp,Bouteloua eriopodaSubtotal 318 354 267 295 298 237 199 320 407 438ANNUAL GRASSESAristida annualChloris annualEragrostis annualBouteloua annualSubtotalPERENNIAL FORBSGuillemina spp 0 0 9 0 0 0 0 0 0 0Sida procumbens 11 3 0 0 0 5 0 0 0 0Hoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 0 0 20Dalea spp 0 0 4 0 2 0 0 0 0 0Malva sppLeguminoseSubtotal 11 3 13 0 2 5 0 0 0 20ANNUAL FORBSHairy forb 0 0 0 0 0 0 0 0 0 47Heteroteca spp 13 0 12 0 9 0 294 0 39 35Grindelia sppCompositaeAnnual Forb 0 0 23 0 0 0 0 0 57 7Argemone mexicanaCyperacea 0 0 0 0 0 0 0 0 4 0Tronadorcillo 0 2 0 0 0 0 0 0 0 0Spharalcea spp 0 0 0 0 4 0 0 0 0 0Ceniza 0 0 24 0 9 0 0 0 0 0Paronichya spp.Aphanosteohus spp 0 0 0 0 0 14 0 96 0 0Gnaphalium canescens 0 30 0 0 0 0 0 0 0 0Hypericum spp 0 0 16 0 0 7 0 0 0 0Euphorbia spp 0 0 0 0 0 2 0 0 0 0LeguminoseCebollinCompositae 2Subtotal 13 32 75 0 22 23 294 96 100 89

88

Table 4.2 List of species sampled Fall 1994: Coverage (cm/1200cm) lenght Ranch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10

SPECIESSHRUBSMimosa sppSubtotalPERENNIAL GRASSESBouteloua gracilis 268 295 195 70 70 198 89 170 188 227Aristida adcensionis 54 3 3 0 5 43 38 11 42 20Hilaria belangeri 0 0 0 43 0 0 0 0 0 0Panicum spp 0 0 0 5 0 0 0 0 0 0Hilaria mutica 0 0 0 152 0 0 0 20 0 0Botrhiocloa barbinodis 0 0 0 22 0 0 0 0 0 0Bouteloua curtipendula 6 0 0 0 64 0 24 0 0 12Bouteloua hirsuta 0 0 0 0 128 3 0 0 0 10Lycurus phleoides 0 0 0 0 4 48 29 0 44 13Schizachirium spp.Mulhenbergia spp, 0 0 0 0 14 0 0 0 0 0Bouteloua eriopodaSubtotal 328 298 198 292 285 292 180 201 274 282ANNUAL GRASSESAristida annualChloris annualEragrostis annualBouteloua annualSubtotal 0 0 0 0 0 0 0 0 0 0PERENNIAL FORBSGuillemina sppSida procumbensHoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 2 0 0Dalea sppMalva spp 0 0 0 0 0 0 0 0 3 0LeguminoseSubtotal 0 0 0 0 0 0 0 2 3 0ANNUAL FORBSHairy forbHeteroteca sppGrindelia sppCompositae 0 0 0 4 0 0 0 0 0 0Annual Forb 0 0 3 0 0 0 0 0 0 0Argemone mexicana 0 0 2 0 0 0 0 0 0 0CyperaceaTronadorcilloSpharalcea sppCenizaParonichya spp.Aphanosteohus sppGnaphalium canescensHypericum sppEuphorbia sppLeguminose 0 0 0 0 0 0 6 0 5 0CebollinCompositae 2Subtotal 0 0 5 4 0 0 6 0 5 0

89

Table 4.3 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10

SPECIESSHRUBSMimosa sppSubtotalPERENNIAL GRASSESBouteloua gracilis 198 177 77 3 144 113 0 95 33 202Aristida adcensionis 0 0 0 0 0 4 0 5 0 0Hilaria belangeri 0 0 0 20 0 0 0 0 0 0Panicum spp 0 0 1 0 0 0 0 0 0 0Hilaria muticaBotrhiocloa barbinodisBouteloua curtipendula 0 0 0 0 91 0 0 0 20 0Bouteloua hirsuta 0 0 0 0 15 12 0 12 0 0Lycurus phleoides 0 0 0 0 0 19 0 0 0 0Schizachirium spp.Mulhenbergia spp, 0 0 0 0 13 0 0 0 6 21Bouteloua eriopodaSubtotal 198 177 78 23 263 148 0 112 59 223ANNUAL GRASSESAristida annualChloris annual 0 0 1 3 0 0 0 0 0 0Eragrostis annual 0 0 16 0 0 0 74 0 0 0Bouteloua annualSubtotal 0 0 17 3 0 0 74 0 0 0PERENNIAL FORBSGuillemina sppSida procumbensHoffmansegia spp.Solanum eleagnigolium 0 0 0 0 0 0 0 0 1 0Dalea sppMalva sppLeguminose 0 0 0 0 0 0 5 0 0 0Subtotal 0 0 0 0 0 0 5 0 1 0ANNUAL FORBSHairy forbHeteroteca sppGrindelia sppCompositae 5 0 0 0 0 0 0 7 0 0Annual Forb 0 2 0 3 1 1 0 4 22 0Argemone mexicanaCyperaceaTronadorcilloSpharalcea sppCenizaParonichya spp.Aphanosteohus sppGnaphalium canescensHypericum sppEuphorbia sppLeguminoseCebollinCompositae 2 0 4 0 3 1 3 0 0 3 5Subtotal 5 6 0 6 2 4 0 11 25 5

90

Table 4.4 List of of species sampled Fall1993 :Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIESSHRUBSMimosa spp. 0 0 168 435 335 0 0 0 0 0 0 0 0 0 0 0 0 0Condelia sppSubotal 0 0 168 435 335 0 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 112 168 213 212 41 90 272 172 220 92 297 248 190 97 288 151 233 112Aristida spp 25 39 22 34 0 14 61 44 50 0 8 12 5 8 25 2 41 23Lycurus phleoides 27 4 8 7 7 65 0 22 1 83 20 28 24 55 0 29 0 29Microchloa kuntii 29 3 0 0 0 0 0 8 4 9 2 0 0 3 0 3 3 9Mulhenbergia spp 0 0 2 0 0 9 0 0 0 0 0 0 0 0 0 12 0 22Elyonurus barbiculmisSchizachirium spp. 0 0 0 11 11 0 0 0 0 0 0 0 0 0 0 58 0 0Bouteloua hirsuta 7 0 0 0 0 73 0 0 0 0 0 0 0 75 0 0 0 0Botriochloa barbinodis 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 200 214 245 264 59 251 333 246 275 184 327 288 219 238 313 255 277 195ANNUAL GRASSESEragrostis annual 0 1 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4Bouteloua annualPanicum annualAristida annualChloris annualSubotal 0 1 6 0 1 0 0 0 0 0 0 0 0 0 0 0 0 4PERENNIAL FORBSDalea spp. 5 3 0 0 0 6 0 0 0 0 0 0 0 0 0 13 0 3Drymaria arenarioidesYerbaniz 0 0 5 31 0 0 0 0 0 0 0 0 0 0 0 0 0 0Guillemina sppZinnia sppPerennial Forb 3 3 13 0 0 0 0 1 0 0 5 0 0 0 0 0 0 3Croton spp 0 0 0 0 45 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 8 6 18 31 45 6 0 1 0 0 5 0 0 0 0 13 0 6ANNUAL FORBSRed forb 24 0 0 0 14 0 0 0 0 0 0 0 34 0 0 0 0 0Annual ForbHairy forbForb 2Lepidium sppVigueria sppForb 3Little strawberryCyperaceaBig forb 0 0 0 0 0 170 0 0 0 1 0 0 0 0 0 0 0 0Star forb 0 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Gnaphalium canescen 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0Composite 0 0 0 0 10 0 0 1 0 0 0 0 3 0 0 0 0 0Eringium spp. 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0Grape weed 0 0 0 0 0 0 0 0 0 0 0 0 34 0 0 0 0 0Subtotal 24 16 0 0 27 170 0 1 0 1 0 0 71 0 0 0 0 0

91

Table 4.5 List of species sampled fall 1994: Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIESSHRUBSMimosa spp. 0 0 190 458 258 0 0 0 0 0 0 0 0 0 0 0 0 0Condelia sppSubotal 0 0 190 458 258 0 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 130 202 0 113 16 108 237 191 258 88 165 166 197 143 237 195 210 111Aristida spp 51 46 36 24 0 22 14 7 8 3 31 8 9 17 0 0 40 20Lycurus phleoides 20 24 0 16 7 75 0 28 5 56 29 25 25 57 0 11 4 15Microchloa kuntii 0 0 18 0 8 28 0 0 0 0 0 0 0 0 0 0 0 21Mulhenbergia spp 0 0 0 0 0 22 0 0 0 0 0 0 0 0 0 7 0 23Elyonurus barbiculmis 0 0 0 0 0 0 8 0 7 19 18 3 0 0 0 0 0 4Schizachirium spp. 0 0 0 5 13 0 0 0 0 0 0 24 0 0 0 86 0 0Bouteloua hirsuta 6 0 0 0 0 0 0 0 0 0 0 0 0 25 0 0 0 0Botriochloa barbinodisSubtotal 207 272 54 158 44 255 259 226 278 166 243 226 231 242 237 299 254 194ANNUAL GRASSESEragrostis annualBouteloua annualPanicum annual 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3Aristida annualChloris annualSubotal 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3PERENNIAL FORBSDalea spp. 0 0 14 3 64 0 0 0 0 2 0 0 0 6 0 0 0 1Drymaria arenarioides 4 8 0 0 14 26 0 0 0 0 3 0 0 1 0 0 0 2Yerbaniz 3 0 0 14 0 0 0 0 0 0 0 0 0 0 0 0 0 0Guillemina spp 0 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Zinnia spp 0 0 18 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Perennial ForbCroton sppSubtotal 7 18 32 17 78 26 0 0 0 2 3 0 0 7 0 0 0 3ANNUAL FORBSRed forb 5 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Annual Forb 3 0 0 1 4 0 0 0 0 0 0 0 0 0 0 0 0 0Hairy forb 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Forb 2 5 0 0 0 31 5 0 0 0 0 0 0 0 0 0 0 0 0Lepidium spp 0 6 0 0 0 0 0 16 0 0 0 0 0 0 0 2 0 2Vigueria spp 0 0 0 0 109 0 0 0 0 0 0 0 0 0 0 0 0 0Forb 3 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0Little strawberry 0 0 0 0 0 0 0 0 0 0 0 0 22 0 0 0 0 0Cyperacea 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0Big forb 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 47Star forbGnaphalium canescensCompositeEringium spp.Grape weedSubtotal 17 15 0 1 144 6 0 16 0 0 0 0 22 0 0 4 0 49

92

Table 4.6 List of species sampled Fall 2005:Cover (cm/1200cm) lengthRanch 2 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18SPECIES SHRUBSMimosa spp. 0 0 210 502 298 15 0 0 0 0 0 0 0 0 0 0 0 0Condelia spp 0 0 0 0 0 60 0 0 0 0 0 0 0 0 0 0 0 0Subotal 0 0 210 502 298 75 0 0 0 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESBouteloua gracilis 173 95 111 28 46 71 51 24 231 57 71 73 28 46 81 44 99 48Aristida spp 0 7 3 0 0 31 5 1 0 0 7 3 0 9 12 7 0 7Lycurus phleoides 0 0 0 0 15 2 0 15 0 0 0 0 0 2 0 0 0 0Microchloa kuntii 0 1 0 0 0 1 7 0 1 0 7 0 0 0 0 2 0 21Mulhenbergia 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 0 0 0Schizachirium spp. 0 0 0 0 9 0 0 0 0 0 0 31 0 0 0 0 0 0Bouteloua hirsuta 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 173 103 114 28 70 109 63 40 232 57 97 107 28 57 93 53 99 76ANNUAL GRASSESEragrostis annual 0 0 0 0 0 0 0 0 2 0 0 3 2 0 0 4 0 3Bouteloua annual 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0Chloris annual 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 2 0 0Aristida annual 0 0 0 0 0 0 0 1 0 0 0 0Subotal 0 0 0 0 0 0 0 1 2 0 0 3 2 2 0 6 0 3PERENNIAL FORBSDalea spp. 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0Subtotal 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0ANNUAL FORBSRed forb 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2Annual Forb 0 5 0 0 0 0 0 0 0 0 0 0 0 1 3 0 0 0Star forb 4 0 0 0 0 0 1 0 0 0 0 0Subotal 5 5 0 0 0 0 1 0 0 0 0 0 0 1 3 0 0 2

93

Table 4.7 List of species sampled Fall 1993: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissima 19 0 0 2 0 0 10 0 3Ephedra sp. 0 0 0 0 0 10 40 0 38Prosopis sp. 0 55 0 172 0 361 0 0 40Mimosa spp. 0 0 0 0 0 0 0 0 0Condelia spp.Subtotal 19 55 0 174 0 371 50 0 81SHRUBS-LIKEMenodora like 0 0 0 63 0 0 0 0 0Xantocephalum sarotrae 15 0 1 0 0 0 0 0 0Subtotal 15 0 1 63 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 0 0 13 0 0 0 85 44 31Bouteloua gracilis 0 48 0 0 0 0 0 0 27Mulhenbergia porteri 0 0 0 0 0 0 2 3 7Botrichloa barbinodis 0 34 0 0 0 0 0 0 0Setaria macrostachya 0 8 0 4 0 10 0 0 0Digitaria californica 0 0 0 0 7 0 0 0 0Cenchrus incertus 4 1 0 0 0 0 0 0 1Eneapogon desvauxii 2 1 0 0 0 0 0 0 0Panicun obtusum 0 0 0 0 0 0 5 0 0Aristida spp 25 36 71 6 0 10 0 0 0Sporobolus airoidesPanicum halliSubotal 31 128 84 10 7 20 92 47 66ANNUAL GRASSESBouteloua curtipendula (annual)Eragrostis annual 0 0 0 0 9 0 0 0 4Aristida annual 14 10 9 11 42 13 5 12 21Bouteloua annual 3 10 0 4 0 2 0 1 19Panicum annual 0 6 13 18 20 3 0 0 0Chloris annual 1 0 2 1 20 17 0 0 2Mulhenbergia annual 7 0 0 0 0 0 0 0 0Subtotal 25 26 24 34 91 35 5 13 46PERENNIAL FORBSSida procumbens 18 1 0 32 42 0 0 0 0Legume 0 0 1Calcomeca 0 0 0 0 1 0 0 0 0Hoffmansegia spp 29 48 97 23 5 2 0 0 0Forb perennial 0 0 0 2 0 0 38 3 14Zinnia spp 5 0 0 0 56 0 0 0 1Croton potsii 5 0 0 0 0 0 0 0 0Cassia spp.Solanum eleagnifoliumSubtotal 57 49 97 57 104 2 38 3 16ANNUAL FORBSEvolvolus spp 19 32 0 16 0 0 0 0 0Cotton forb 0 0 0 0 0 0 0 0 1Curly forb 11 5 0 0 0 0 0 1 0Amaranths spp 0 0 0 1 6 3 0 0 0Eringium spp. 0 1 1 0 1 0 0 0 0Subtotal 30 38 1 17 7 3 0 1 1

94

Table 4.8 List of species sampled Fall 1994: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissimaEphedra sp. 0 0 0 0 0 0 18 0 30Prosopis sp. 0 40 0 128 0 331 0 0 51Mimosa spp. 0 0 0 0 0 0 0 0 0Condelia spp.Subtotal 0 40 0 128 0 331 18 0 81SHRUBS-LIKEMenodora likeGutierreza sarotraeSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 3 0 8 0 0 0 46 29 10Bouteloua gracilis 0 12 0 0 0 0 0 0 30Mulhenbergia porteri 0 0 0Botrichloa barbinodis 0 11 0 0 0 0Setaria macrostachya 0 0 0 50 0 0 0 0 0Digitaria californica 0 0 0 0 2 3 0 0 0Cenchrus incertusEneapogon desvauxiiPanicun obtusum 0 0 0 0 0 0 0 0 0Aristida spp 12 30 19 22 0 11 0 0 0Sporobolus airoides 7 0 0 0 0 0 0 0 0Panicum halliSubotal 22 53 27 72 2 14 46 29 40ANNUAL GRASSESBouteloua curtipendula (annual)Eragrostis annualAristida annual 2 0 0 3 2 0 0 1 12Bouteloua annualPanicum annual 0 0 5 0 0 0 0 0 0Chloris annualMulhenbergia annualSubtotal 2 0 5 3 2 0 0 1 12PERENNIAL FORBSSida procumbens 32 1 0 23 108 0 0 0 0LegumeCalcomecaHoffmansegia spp 1 0 0 3 0 0 3 14 2Forb perennialZinnia spp 2 0 0 0 7 0 0 0 0Croton potsii 16 8 0 0 0 0 0 0 0Cassia spp. 10 0 0 0 0 0 2 0 0Solanum eleagnifolium 0 0 0 0 0 3 0 0 2Subtotal 61 9 0 26 115 3 5 14 4ANNUAL FORBSEvolvolus spp 7 21 0 0 3 4 0 0 0Annual forb 1Composite 2 0 1 2 0 0 0 0 0Subtotal 9 21 1 2 3 4 0 0 0

95

Table 4.9 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 3 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSAcacia angustissima 5 0 0 0 0 4 0 0 0Ephedra sp.Prosopis sp. 0 0 0 134 0 472 0 0 30Mimosa spp.Condelia spp.Subtotal 5 0 0 134 0 476 0 0 30SHRUBS-LIKEMenodora likeXantocephalum sarotraeSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL GRASSESEragrostis lehmanniana 61 102 49 4 0 6 64 70 92Bouteloua gracilis 0 10 38 0 0 0 0 0 30Mulhenbergia porteriBotrichloa barbinodisSetaria macrostachyaDigitaria californica 0 0 0 25 2 1 0 0 0Cenchrus incertusEneapogon desvauxii 0 2 0 0 0 0 0 0 0Panicun obtusumAristida spp 12 9 1 18 8 0 9 0 0Sporobolus airoidesPanicum halliSubotal 73 123 88 47 10 7 73 70 122ANNUAL GRASSESBouteloua curtipendula (annual) 0 0 0 0 0 1 0 0 0Eragrostis annual 0 0 0 0 5 7 1 0 0Aristida annualBouteloua annual 0 0 0 0 4 0 0 0 0Panicum annualChloris annualMulhenbergia annualSubtotal 0.0 0.0 0.0 0.0 9.0 8.0 1.0 0.0 0.0PERENNIAL FORBSSida procumbens 1 0 0 0 0 0 0 0 0LegumeCalcomecaHoffmansegia spp 0.0 0.0 0.0 0.0 0 0 0 3 0Forb perennialZinnia sppCroton potsiiCassisa spSolanum eleagnifolium 0 0 0 2 0 0 0 0 0Subtotal 1 0 0 2 0 0 0 0 0ANNUAL FORBSEvolvolus spp 0 1 0 0 0 2 0 0 0Annual forb 1 1 0 0 0 1 0 0 0 0CompositeCotton forbSubtotal 1 1 0 0 1 2 0 0 0

96

Table 4.10 List of species sampled Fall 1993: Cover (cm/1200cm) lengthRanch 4 T1 T2 T4 T5 T6 T7 T8 T9 T10SPECIESSHRUBSParthenium incanum 0 0 21 120 0 70 0 79 0Ephedra sp.Prosopis sp. 0 0 0 0 290 174 0 187 0Mimosa spp 30 0 0 0 0 0 4 0 21Flourencia cernua 0 0 215 49 0 0 0 0 0Atriplex sppSubtotal 30 0 236 169 290 244 4 266 21.0SHRUBS-LIKEXantocephalum sarotrae 417 147 49 166 155 138 333 157 261Agave sppSubtotal 417 147 49 166 155 138 333 157 261PERENNIAL GRASSESLycurus phleoides 0 0 0 0 6 0 0 0 0Bouteloua gracilis 0 20 0 0 2 0 0 0 0Bouteloua eriopoda 0 0 0 0 7 0 0 0 0Botrichloa barbinodis 0 0 0 0 0 0 0 0 3Setaria macrostachya 0 0 8 0 6 11 4 14 7Digitaria californica 0 19 17 0 4 0 0 12 21Erioneuron pulchellum 0 0 0 3 0 6 0 0 0Eneapogon desvauxii 1 8 0 0 2 0 3 0 0Aristida adscencionis 7 6 1 0 10 1 2 3 2Aristida spp 5 5 9 0 0 2 0 0 12Subotal 13 58 35 3 37 20 9 29 45 ANNUAL GRASSESEragrostis annual 10 0 0 0 6 1 5 3 2Aristida annualBouteloua barbata 1 3 0 0 1 1 1 3 3Panicum annual 7 4 0 0 3 2 1 0 1Chloris annual 0 0 0 0 0 0 0 0 3Bouteloua aristirioides 0 0 0 0 0 0 18 5 3Subtotal 18 7 0 0 10 4 25 11 12PERENNIAL FORBSSida procumbens 15 3 9 6 4 0 8 0 0Legume 6 0 0 0 0 0 0 0 0Solanum eleagnifoliumHoffmansegia spp 0 1 0 0 0 0 0 0 0Zinnia spp 0 0 0 0 0 16 5 0 0Legume2 0 0 0 4 0 0Croton potsii 0 0 0Dichondria argentea 0 0 0 0 10 0 0 0 0Guillemina sppLegume 3 0 0 0 0 0 150 0 0 99Legume 4 0 0 0 0 0 0 6 0 0Cassia sppSubtotal 21 4 9 10 14 166 19 0 99ANNUAL FORBSEvolvolus sppAnnual forb 1Ddysodia spp 0 0 0 6 0 0 0 2 0Subtotal 0 0 0 6 0 0 0 2 0

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Table 4.11 List of species sampled Fall 1994: Cover (cm/1200cm) lengthRanch 4 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSParthenium incanum 0 0 17 119 0 60 0 84 0Ephedra sp.Prosopis sp. 0 0 0 0 320 127 0 393 17Mimosa sppFlourencia cernua 0 0 121 76 0 0 0 0 0Atriplex spp 0 0 0 0 0 5 0 0 0Subtotal 0 0 138 195 320 192 0 477 17SHRUBS-LIKEXantocephalum sarotrae 309 59 5 116 0 81 214 64 0Agave sppSubtotal 309 59 5 116 0 81 214 64 0PERENNIAL GRASSESLycurus phleoidesBouteloua gracilis 0 19 0 0 11 0 0 0 0Bouteloua eriopoda 0 0 0 0 6 0 0 0 0Botrichloa barbinodisSetaria macrostachya 0 0 0 0 0 4 0 6 0Digitaria californica 0 0 5 0 5 4 0 3 4Erioneuron pulchellumEneapogon desvauxiiAristida adscencionisAristida spp 0 0 5 0 1 0 0 0 0Subotal 0 19 10 0 23 8 0 9 4 ANNUAL GRASSESEragrostis annualAristida annualBouteloua barbataPanicum annualChloris annualBouteloua aristirioidesSubtotal 0 0 0 0 0 0 0 0 0PERENNIAL FORBSSida procumbens 5 2 0 0 0 0 0 0 0Legume 0Solanum eleagnifoliumHoffmansegia sppZinnia spp 0 0 0 0 4 0 0 0 0Legume2Croton potsii 0 0 0 0 0 3 0 0 0Dichondria argentea 0 0 0 0 2 0 0 0 0Guillemina sppLegume 3Legume 4Cassia spp 0 3 0 0 0 0 0 0 0Subtotal 5 5 0 0 6 3 0 0 0ANNUAL FORBSEvolvolus sppAnnual forb 1Ddysodia sppSubtotal 0 0 0 0 0 0 0 0 0

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Table 4.12 List of species sampled Fall 2005: Cover (cm/1200cm) lengthRanch 4 T1 T2 T3 T4 T5 T6 T7 T8 T9SPECIESSHRUBSParthenium incanumEphedra sp. 0 100 0 0 0 0 0 0 0Prosopis sp. 0 0 182 0 87 0 200 0 217Mimosa sppFlourencia cernua 0 0 172 314 0 0 0 0 0Atriplex sppSubtotal 0 100 354 314 87 0 200 0 217SHRUBS-LIKEXantocephalum sarotrae 54 69 0 0 0 9 19 55 75Agave spp 0 0 0 0 0 0 0 0 32Subtotal 54 69 0 0 0 9 19 55 107PERENNIAL GRASSESLycurus phleoidesBouteloua gracilis 0 0 0 0 2 0 0 0 0Bouteloua eriopoda 0 0 0 0 7 0 0 0 0Botrichloa barbinodisSetaria macrostachya 0 0 0 0 0 0 0 0 4Digitaria californicaErioneuron pulchellumEneapogon desvauxiiAristida adscencionisAristida spp 0 0 0 4 0 0 0 0 0Subotal 0 0 0 4 9 0 0 0 4 ANNUAL GRASSESEragrostis annualAristida annual 1 0 0 0 0 0 0 0 4Subtotal 1 0 0 0 0 0 0 0 4PERENNIAL FORBSSida procumbensLegumeSolanum eleagnifolium 0 0 0 0 0 0 1 1 0Hoffmansegia spp 0 1 0 0 0 0 0 1 0Zinnia sppLegume2Croton potsiiDichondria argentea 0 49 0 0 0 0 0 0 0Guillemina spp 4 0 0 0 0 0 0 0 0Legume 3Legume 4Cassia spp 0 9 0 0 2 0 0 0 4Subtotal 4 59 0 0 2 0 1 2 4ANNUAL FORBSEvolvolus spp 0 3 0 0 0 0 0 0 0Annual forb 1 1 1 0 0 0 0 0 0 0Ddysodia sppVigueria spp 0 0 0 0 0 79 0 0 0Red forb 0 0 0 0 5 2 0 0 0Big forb 2 1 0 0 0 0 0 0 0Salsola spp. 0 0 0 0 0 1 0 0 0Subtotal 3 5 0 0 5 82 0 0 0

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Table 4.13 Ranch 1 -List of species sampled : Density (plants/m2) SPECIES 1993 fall 1994 Fall 2005 FallPERENNIAL GRASSESBouteloua gracilis 67.7 94.7 32.1Aristida spp 12.3 0.4Bouteloua curtipendula 1.0 3.7 0.8Lycurus phleoides 1.3 4.0 0.2Botriochloa barbinodis 0.3 0.7 0.2Bouteloua hirsuta 2.0 3.0 1.1Hilaria mutica 4.0 3.3 0.4Mulhenbergia spp 0.7Hilaria belangerii 1.7Scleropogon brevifolius 0.4ANNUAL GRASSESAristida annual 11.3Panicum annual 1.7 3.3 0.8Chloris annual 0.3Eragrostis annual 0.3 0.4Bouteloua annual 4.2PERENNIAL FORBSDalea spp 1.0Hoffmansegia spp 0.2Legume 0.7 0.3ANNUAL FORBSComposite 6.9Grindelia spp 0.3Argemone mexicana 0.3Heteroteca spp 11.7Tronadoycillo 0.7Composite 2 20.0 3.1Hierba wide leaf 0.4Grey forb 0.2Forb annual 1.3Woody forb 0.4SHRUBSMimosa biuncifera 1.0

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Table 4.14 Ranch 2 -List of species sampled : Density (plants/m2)SPECIES Fall 1993 Fall 1994 Fall 1995PERENNIAL GRASSESBouteloua hirsuta 5 1.0Bouteloua gracilis 31 78.3 34.67Elyonurus barbiculmis 1Lycurus phleoides 6.3 10.3 5.11Microchloa kunthii 26.3 16.0 0.67Aristida spp 0.7 10.0 4.44Mulhenbergia spp 1.0 0.7Schyzachirium cirratus 0.3 0.3Eneapoon desvauxii 0.3 0.3ANNUAL GRASSESEragrostis annual 2.7 2.00Panicum annual 0.3Chloris annual 0.22Aristida annual 1.0 0.22PERENNIAL FORBSDalea spp 1.0Forb perenne 3.7Dalea sp 2 0.7Gnaphalium spp 0.7Legume 1 0.3 0.46Zinnia spp 0.3Croton spp 1.3 3.7Yerbanis 0.3ANNUAL FORBSStevia serrata 0.7Forb wide leaf 1.3Forb 6.7 2.01Composite 0.7 2.7Star forb 0.3Drymaria arenarioides 0.3Haiy forb 8.3 0.7 0.07Strawberry forb 0.3forbannual 2 0.23Red forb 0.23SRHUBSMimosa spp 8.3 0.3 0.07

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Table 4.15 Ranch 3 -List of species sampled: Density (plants/m2)SPECIES 1993 FALL 1994 FALL 2005 FALLPERENNIAL GRASSESBouteloua gracilis 2 0.7 0.7Eragrostis lehmanniana 24.7 1.0 51.8Aristida spp 4.3 9 14.7Setaria macrostachya 0.3 1.6Panicum obtusum 0.3Mulhenbergia porteri 0.7Digitaria californica 0.3 0.3 0.4Sporobolus airoides 0.0 0.3Botriochloa barbinodis 0.2ANNUAL GRASSESPanicum annual 13 1 0.2Aristida annual 48.7 9.7Bouteloua annual 8.7 1.8Cencrus incertus 0.3Eneapogon desvauxii 0.3 0.2Eragristis annual 1.0 2.0PERENNIAL FORBSZinnia spp 0.7 0.7Croton spp 2.0 2.0 0.5Cassia spp 1.0 0.7Legume 6.7Hoffmansegia spp 34.0 1.0Sida procubens 16.7 7.7 0.4Soalnum eleagnifolium 0.2ANNUAL FORBSEuphorbia spp 37.7Enredadera 2.0Forb 0.3 0.3 1.1Evolvolus spp 0.7 0.3 0.4Amaranthus spp 2.7Eringium app 0.3Calcomeca 0.3Forb 0.3Drymaria arenarioidesVerbena sppEysenhardtia sppRed forbComposite 0.3Little onion 0.4SHRUBS plants/ha plants/ha plants/haMimosa biuncifera 0.3Condalia ericoidesEphedra trifurca 350.7Prosopis glandulosa 511.3 78.6Acacia gregii 37.7 39.3Legume shrub 0.03

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Table 4.16 Ranch 4-List of species sampled: Density (plants/m2)SPECIES 1993 FALL 1994 FALL 2005 FALLPERRENNIAL GRASSESAristida adcencionis 17.3Eneapogon desvauxii 2.3Digitaria californica 0.2 1.67Bouteloua gracilis 0.7 0.67Aristida spp 1.7 0.67Chloris virgata 0.4Setaria macrostachya 2.3Erioneuron pulchellum 1.1Botriochloa barbinodis 0.7Bouteloua eropoda 0.0 0.67 0.2ANNUAL GRASSESPanicum annual 20.2 0.2Eragostis annual. 23.8 2.2Chloris annual 4.4Bouteloua barbata 3.9 1.2Bouteloua aristirioides 27.7Aristida annual 1.00 2.1PERENNIAL FORBSCassia spp 0.67 1.5Solanum eleagniflium 0.2 0.2Dichondra argentea 0.7 0.4Legumes 2.2Legume 2 14.0Dysodia spp 0.3Calcomeca 0.3Croton potsii 0.7 0.33 0.9Guillemina densa 3.3Hoffmansegia spp 0.3 0.9Zinnia spp 0.7Sida procumbens 15.1 0.67Euphorbia spp 0.2ANNUAL FORBSForb 0.3 0.9Hybiscus spp 0.3Evolvolus spp 0.4 Ipomoea spp 0.2White flower forb 3.3Red forb 0.9Vigueria spp 0.2Tall forb 0.7SHRUBS SSHRUBS-LIKE plants/ha plants/ha plants/haEphedra spp 333 156 39Prosopis glandulosa 767 1334 416Yucca spp 33Flourencia cernua 333 511 472Parthenium incanum 367 747 157Atriplex canescens 33 118 39Koeberlina spinulosa 267Mimosa spp 1367 38Budleja scordioides 133Condalia ericoides 393Xantocephalum sarotrae 14500 11233 815Brickelia spinulosa

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Forage Production Samples Table 4.17 Forage Production Ranch 1 Forage Production (Kg DM/Ha)RANCH 1 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture

4 7 8 4 7 8 4 7 8Sample 1 2220 720 1060 260 100 40 880 1075 40Sample 2 2640 460 400 240 60 120 270 290 222Sample 3 1770 460 1220 460 70 440 270 425 200Sample 4 1500 740 720 540 320 270 248 262 540Sample 5 730 1100 1340 700 280 270 185 340 970Sample 6 848 660 1420 440 220 640 248 700 335

1100 130 452Mean 1618 690 1037 440 175 272 394 515 350 Table 4.18 Forage Production Ranch 2 Forage Production (Kg DM/Ha)RANCH 2 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture

1 2 3 1 2 3 1 2 3Sample 1 1080 290 1920 440 0 820 280 345 225Sample 2 1080 506 1740 592 520 220 675 565 590Sample 3 880 1730 1160 200 240 400 245 1092 608Sample 4 1380 880 906 360 360 500 225 542 325Sample 5 340 1144 1300 230 360 580 298 693 682Sample 6 660 453 1740 2080 580 1020 400 562 425Sample 7 1173 460Mean 903 882 1461 650 360 673 353 633 475

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Forage Production Samples Table 4.19 Forage Production Ranch 3 Forage Production (Kg DM/Ha)RANCH 3 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture

2 12 16 2 12 16 2 12 16Sample 1 560 700 480 200 820 360 630 692 360Sample 2 920 1840 1080 320 310 440 685 431 1041Sample 3 700 2280 1320 120 280 60 1630 1305 1939Sample 4 660 740 1760 60 240 320 903 215 1315Sample 5 480 1140 540 40 520 60 1010 970 507Sample 6 460 1840 1233 100 0 885 653 435

Mean 630 1252 1233 140 434 206 932 957 711 Table 4.20 Forage Production Ranch 4 Forage Production (Kg DM/Ha)RANCH 4 FALL 1993 FALL1994 FALL2005Samples Pasture Pasture Pasture

1 2 8 1 2 8 1 2 8Sample 1 340 940 220 0 0 0 41 35 472Sample 2 600 300 360 0 0 0 60 203 95Sample 3 1780 820 160 0 0 0 60 119 121Sample 4 740 540 0 0 0 0 80 61 62Sample 5 1640 240 500 0 0 0 85 72 30Sample 6 500 280 160 0 0 0 30 0 5

Mean 933 520 206 0 0 0 59 81 130

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APPENDIX B

STATISTICAL ANALYSIS OUTPUTS

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BASAL COVER NORMALITY TEST ----------------------- trt=1 ----------------------------- The UNIVARIATE Procedure Variable: Experimental errors Test --Statistic--- -----p Value------ Shapiro-Wilk W 0.971806 Pr < W 0.0619 Kolmogorov-Smirnov D 0.092634 Pr > D 0.0752 Cramer-von Mises W-Sq 0.12934 Pr > W-Sq 0.0453 Anderson-Darling A-Sq 0.758379 Pr > A-Sq 0.0472 Quantiles (Definition 5) Quantile Estimate 95% 89.6597 90% 75.5065 75% Q3 33.2668 50% Median 11.6851 25% Q1 -35.2077 10% -67.4935 5% -110.3403 1% -192.4935 0% Min -192.4935 Extreme Observations ------Lowest----- ------Highest----- Value Obs Value Obs -192.493 15 89.6597 66 -170.315 43 108.0882 9 -160.315 41 129.6597 61 -133.340 63 139.0882 10 -110.340 60 146.0780 75

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------------------ trt=1 ----------------------------- The UNIVARIATE Procedure Variable: ee Stem Leaf # Boxplot 14 6 1 0 12 09 2 0 10 8 1 | 8 2570 4 | 6 24566 5 | 4 014558 6 | 2 011333468890067 15 +-----+ 0 471222335779 12 *--+--* -0 630765410 9 | | -2 732299310 9 +-----+ -4 88665186 8 | -6 47421 5 | -8 2 1 | -10 00 2 | -12 3 1 | -14 -16 00 2 0 -18 2 1 0 ----+----+----+----+ Multiply Stem.Leaf by 10**+1 Normal Probability Plot 150+ ++*+ | *+* | +*+ | **** | **** +*** | ****** | ****+ | **** | **** | **** | ***+ | **+ | ++* | +++ * |++++ | * * -190+* +----+----+----+----+----+----+----+----+----+----+ -2 -1 0 +1 +2

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-------------------- trt=2 ----------------------------- The UNIVARIATE Procedure Variable: ee Tests for Normality Test --Statistic--- -----p Value------ Shapiro-Wilk W 0.967636 Pr < W 0.1515 Kolmogorov-Smirnov D 0.095054 Pr > D >0.1500 Cramer-von Mises W-Sq 0.071719 Pr > W-Sq >0.2500 Anderson-Darling A-Sq 0.536992 Pr > A-Sq 0.1677 Quantiles (Definition 5) Quantile Estimate 75% Q3 14.29085 50% Median 1.88889 25% Q1 -11.70915 10% -43.15359 5% -51.70915 1% -57.48693 0% Min -57.48693 Extreme Observations ------Lowest----- -----Highest----- Value Obs Value Obs -57.4869 89 29.2908 123 -54.4869 88 40.9314 95 -51.7092 126 63.2908 129 -48.7092 125 63.5131 86 -44.4869 90 64.2908 122

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Variable: ee Stem Leaf # Boxplot 6 344 3 0 5 5 4 4 1 1 | 3 | 3 | 2 57889 5 | 2 001 3 | 1 8 1 | 1 0112244 7 +-----+ 0 689 3 | | 0 22223 5 *--+--* -0 42 2 | | -0 8775 4 | | -1 42111111 8 +-----+ -1 876 3 | -2 3 1 | -2 | -3 31 2 | -3 | -4 43 2 | -4 9 1 | -5 42 2 0 -5 7 1 0 ----+----+----+----+ Multiply Stem.Leaf by 10**+1

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Normal Probability Plot 62.5+ * * +* | ++ | + | ++ | *+ | ++ | ++ | ***** | +* | +*** | *** | ** 2.5+ *** | * | ** | **** | **++ | *++ + | ** | ++ | ++** | ++ * | * * -57.5+ * ++ +----+----+----+----+----+----+----+----+----+----+ -2 -1 0 +1 +2

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Schematic Plots | 150 + 0 | 0 | | | | 100 + | | | | | | | 0 50 + | | +-----+ | | | | | | *-----* +-----+ 0 + | + | *--+--* | | | +-----+ | | | | +-----+ | -50 + | 0 | 0 | | | | -100 + | | | | | | | -150 + | 0 | 0 | 0 -200 + ------------+-----------+----------- trt 1 2

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ANALYSIS OF VARIANCE WITH REPEATED MEASUREMENTS OF PERENNIAL GRASSES BASAL COVER INITIAL SURVEY USED AS COVARIATE

Basal Cover The Mixed Procedure Model Information Data Set WORK.FORAGE Dependent Variable y Covariance Structure Compound Symmetry Subject Effect rep(trt*ranch) Estimation Method REML Residual Variance Method Profile Fixed Effects SE Method Model-Based Degrees of Freedom Method Between-Within Class Level Information Class Levels Values trt 2 1 2 ranch 4 1 2 3 4 year 2 2 3 rep 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Dimensions Covariance Parameters 2 Columns in X 14 Columns in Z 0 Subjects 46 Max Obs Per Subject 2 Number of Observations Number of Observations Read 92 Number of Observations Used 92 Number of Observations Not Used 0 Iteration History Iteration Evaluations -2 Res Log Like Criterion

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0 1 504.02032189 1 1 502.83193946 0.00000000 Convergence criteria met. The Mixed Procedure Covariance Parameter Estimates Cov Parm Subject Estimate CS rep(trt*ranch) 2.7461 Residual 13.8130 Fit Statistics -2 Res Log Likelihood 502.8 AIC (smaller is better) 506.8 AICC (smaller is better) 507.0 BIC (smaller is better) 510.5 Null Model Likelihood Ratio Test DF Chi-Square Pr > ChiSq 1 1.19 0.2757 Type 3 Tests of Fixed Effects Num Den Effect DF DF F Value Pr > F trt 1 41 3.75 0.0599 ranch(trt) 2 41 2.47 0.0967 year 1 44 36.42 <.0001 trt*year 1 44 55.58 <.0001 ini 1 41 14.57 0.0004 Least Squares Means Standard Effect trt year Estimate Error DF t Value Pr > |t| trt 1 11.2194 1.0453 41 10.73 <.0001 trt 2 6.8747 1.3928 41 4.94 <.0001 year 2 11.4428 0.6434 44 17.78 <.0001 year 3 6.6513 0.6434 44 10.34 <.0001 trt*year 1 2 16.5747 1.1573 44 14.32 <.0001

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trt*year 1 3 5.8640 1.1573 44 5.07 <.0001 trt*year 2 2 6.3108 1.5243 44 4.14 0.0002 trt*year 2 3 7.4386 1.5243 44 4.88 <.0001 Differences of Least Squares Means Standard Effect trt year _trt _year Estimate Error DF t Value Pr > |t| trt 1 2 4.3447 2.2448 41 1.94 0.0599 year 2 3 4.7915 0.7939 44 6.03 <.0001 trt*year 1 2 1 3 10.7107 0.9933 44 10.78 <.0001 trt*year 1 2 2 2 10.2639 2.3811 44 4.31 <.0001 trt*year 1 2 2 3 9.1362 2.3811 44 3.84 0.0004 trt*year 1 3 2 2 -0.4468 2.3811 44 -0.19 0.8520 trt*year 1 3 2 3 -1.5746 2.3811 44 -0.66 0.5119 trt*year 2 2 2 3 -1.1278 1.2389 44 -0.91 0.3676

ANALYSIS OF VARIANCE WITH REPEATED MEASUREMENTS OF FORAGE PRODUCTION

Forage Production The Mixed Procedure Model Information Data Set WORK.FORAGE Dependent Variable y Covariance Structure Compound Symmetry Subject Effect rep(trt*ranch) Estimation Method REML Residual Variance Method Profile Fixed Effects SE Method Model-Based Degrees of Freedom Method Between-Within Class Level Information Class Levels Values trt 2 1 2 ranch 4 1 2 3 4 year 2 1 2

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rep 3 1 2 3 Dimensions Covariance Parameters 2 Columns in X 14 Columns in Z 0 Subjects 12 Max Obs Per Subject 3 Number of Observations Number of Observations Read 24 Number of Observations Used 24 Number of Observations Not Used 0 Iteration History Iteration Evaluations -2 Res Log Like Criterion 0 1 246.74455224 1 2 246.47819212 0.00007372 2 1 246.46970588 0.00000096 3 1 246.46960213 0.00000000 Convergence criteria met. Covariance Parameter Estimates Cov Parm Subject Estimate CS rep(trt*ranch) 8219.86 Residual 21843 Fit Statistics -2 Res Log Likelihood 246.5 AIC (smaller is better) 250.5 AICC (smaller is better) 251.3 BIC (smaller is better) 251.4 Null Model Likelihood Ratio Test DF Chi-Square Pr > ChiSq 1 0.27 0.6000

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Type 3 Tests of Fixed Effects Num Den Effect DF DF F Value Pr > F trt 1 8 13.42 0.0064 ranch(trt) 2 8 13.64 0.0026 year 1 9 1.30 0.2834 trt*year 1 9 23.02 0.0010 ini 1 9 3.67 0.0875 Least Squares Means Standard Effect trt year Estimate Error DF t Value Pr > |t| trt 1 634.33 56.4819 8 11.23 <.0001 trt 2 339.96 57.1446 8 5.95 0.0003 year 1 521.92 50.0521 9 10.43 <.0001 year 2 452.37 50.7988 9 8.91 <.0001 trt*year 1 1 815.33 70.7844 9 11.52 <.0001 trt*year 1 2 453.33 70.7844 9 6.40 0.0001 trt*year 2 1 228.50 70.7844 9 3.23 0.0104 trt*year 2 2 451.41 72.8811 9 6.19 0.0002 Differences of Least Squares Means Standard Effect trt year _trt _year Estimate Error DF t Value Pr > |t| trt 1 2 294.38 80.3474 8 3.66 0.0064 year 1 2 69.5435 60.9570 9 1.14 0.2834 trt*year 1 1 1 2 362.00 85.3282 9 4.24 0.0022 trt*year 1 1 2 1 586.83 100.10 9 5.86 0.0002 trt*year 1 1 2 2 363.92 101.60 9 3.58 0.0059 trt*year 1 2 2 1 224.83 100.10 9 2.25 0.0513 trt*year 1 2 2 2 1.9204 101.60 9 0.02 0.9853 trt*year 2 1 2 2 -222.91 87.0754 9 -2.56 0.0307

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ANALYSIS OF PRINCIPAL COMPONENTS 1993 Correlation Matrix Shrubs Nonsh PGrass AGrass PForbs Aforbs shrubs 1.0000 0.1382 -.4335 0.0931 0.2132 -.2001 Nonsh 0.1382 1.0000 -.5477 0.1386 0.2298 -.1982 PGrass -.4335 -.5477 1.0000 -.5642 -.4814 0.2688 AGrass 0.0931 0.1386 -.5642 1.0000 0.4652 -.1669 PForbs 0.2132 0.2298 -.4814 0.4652 1.0000 -.1555 Aforbs -.2001 -.1982 0.2688 -.1669 -.1555 1.0000 Eigenvalues of the Correlation Matrix Eigenvalue Difference Proportion Cumulative 1 2.52957310 1.51571697 0.4216 0.4216 2 1.01385614 0.14925262 0.1690 0.5906 3 0.86460351 0.03800371 0.1441 0.7347 4 0.82659980 0.27614764 0.1378 0.8724 5 0.55045216 0.33553688 0.0917 0.9642 6 0.21491528 0.0358 1.0000 Eigenvectors Prin1 Prin2 Prin3 Prin4 Prin5 Prin6 shrubs 0.315964 -.489807 0.578963 0.483857 -.063423 0.294817 Nonsh 0.370130 -.287243 -.770198 0.156433 0.071153 0.397185 PGrass -.563830 0.013842 0.104266 -.166062 0.273844 0.753967 AGrass 0.423224 0.550583 0.130670 -.206832 -.520875 0.431944 PForbs 0.434133 0.386854 0.149831 0.026072 0.799119 0.012328 Aforbs -.278707 0.473912 -.145605 0.818764 -.077600 0.011532

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ANALYSIS OF PINCIPAL COMPONENTS 2005 Correlation Matrix shrubs suffrut. PGrass AGrass PForbs Aforbs shrubs 1.0000 0.1076 -.3642 -.0640 0.0390 -.1349 Suffru. .1076 1.0000 -.3599 -.0414 0.5125 0.0011 PGrass -.3642 -.3599 1.0000 -.2113 -.2153 -.1174 AGrass -.0640 -.0414 -.2113 1.0000 0.0331 -.0767 PForbs 0.0390 0.5125 -.2153 0.0331 1.0000 0.0054 Aforbs -.1349 0.0011 -.1174 -.0767 0.0054 1.0000 Eigenvalues of the Correlation Matrix Eigenvalue Difference Proportion Cumulative 1 1.84295398 0.68205002 0.3072 0.3072 2 1.16090396 0.09614295 0.1935 0.5006 3 1.06476101 0.04035716 0.1775 0.6781 4 1.02440385 0.50461277 0.1707 0.8488 5 0.51979108 0.13260496 0.0866 0.9355 6 0.38718612 0.0645 1.0000 Eigenvectors Prin1 Prin2 Prin3 Prin4 Prin5 Prin6 Shrubs 0.321016 -.587929 -.427109 -.278738 0.409518 0.351379 Suffrut.0.576942 0.296304 -.108566 0.181930 -.485355 0.546706 PGrass -.543011 0.273396 -.201455 0.357891 0.353979 0.580020 AGrass 0.101647 -.349832 0.832876 0.215706 0.160401 0.318347 PForbs 0.508461 0.379124 0.001197 0.337611 0.629868 -.294986 Aforbs 0.019010 0.475059 0.267438 -.774991 0.221276 0.229916

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APPENDIX C

GLOSSARY

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Glossary Animal Unit (AU). One mature, non lactating bovine weighing about 1000 lb (454

kg) or its equivalent in other classes or kind of ungulate herbivores based in animal demand or quantitative forage dry matter intake; assumes a standard daily forage intake of 26 lb (12 kg) on an oven-dry basis.

Brush. Shrubs or small tree considered undesirable from the stand point of

planned use of the area, an undesirable noxious woody plant. Carrying capacity. All nutrient resources available on a given land area, including

not only pasturage but also harvested forage and other feedstuffs used to complement the grazing resources, thereby providing a means of summarizing a total ranch capacity or that allotted to a specific animal enterprise (best usage)

Cell (or cell grazing). A grazing arrangement comprised of numerous subunits

(i.e. paddocks), usually in a rotational grazing system, with a common central component provided with drinking water, animal handling facilities, and access between units.

Climax. The final or stable biotic community in a successional series; it is self

perpetuating and in equilibrium with the physical habitat. Continuous grazing. Allowing animals unrestricted and uninterrupted access to a

grazing land unit for all or most of the grazing season; includes yearlong, growing season, dormant season continuous grazing. Synonym. Continuous stocking.

Deferment. Nongrazing from the breaking of plant dormancy until after seed set

or equivalent stage of vegetative reproduction, accomplished either by delaying the beginning of spring grazing or discontinuing winter grazing early.

Deferred–rotation grazing. A multi unit, one herd grazing system in which

deferment is systematically rotated among the respective grazing land units.

Defoliation. The removal of plant leaves by grazing or browsing, cutting, chemical

defoliant, or natural phenomena such as hail, fire or frost. Dominant. Plant species or species group which has considerable influence or

control over associated plant species.

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Drought. Prolonged dry weather, generally when precipitation is less than ¾ of average for a considerable period of time; period during which plants suffer from lack of water.

Forage mass. The total dry weight of forage per unit area of land, usually above

ground level and at a defined reference level. Forage mass may include forage not accessible to a particular kind of grazing animal.

Forage production. The weight of forage that is produced within a designated

period of time on a given area; expressed as green, air-dry, oven-dry weight and may be qualified as annual, current year’s, or seasonal forage production.

Grazing. The act of eating forage from the standing crop comprised (1) foraging,

the search for forage; (2) defoliation, the removal of forage; and (3) ingesting the forage. Synonym. Herbivory.

Grazing Capacity. (a) The optimal stocking rate that will achieve the target level

of animal performance or other specific objective, while preventing deterioration of the ecosystem. Must consider both management objectives and management intensity to be accurate. (b) Total number of AUM’s produced and available or grazing per acre or from a specific grazing land unit, a grazing allotment, the total ranch, or other specified land area.

Grazing intensity. A general term expressing (1) the amount of animal demand

placed upon the standing crop of forage mass, and (2) the resulting level of plant defoliation made during grazing.

Grazing period. The length of time that grazing animals occupy a grazing area

without interruption. Heavy grazing. A comparative term which indicate that the stocking rate on an

area is relatively greater than that on other similar areas; sometimes erroneously used to mean overgrazing.

Herbaceous. Vegetative growth with little or not woody component; non-woody

component such as graminoids and forbs. Light grazing. A comparative term which indicates that stocking rate on an area is

relatively less than that on other similar areas; sometimes erroneously used to mean undergrazing.

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Native species. A species which is part of the original flora or fauna of the area in question

Nongrazing. The restriction or absence of grazing use on an area for a period of

time , ranging from a short period of a few days to a year or more. Overgrazing. Continued heavy grazing which exceeds the recovery capacity of

the forage plants and creates deterioration of the grazing plants. Overstocking. Placing so many animals on a grazing unit that overuse will result

If continued unchanged to the end of the planned grazing period. Paddock. (a) One of the multiple grazing units or subunits included in a rotation

grazing series. Patch. (a) A specific aggregation of forage plants. (b) A spatial foraging levels

defined as a cluster of feeding station separated from other potential feeding stations ; requires a break in a foraging for transit from one patch to another patch.

Range condition. Historically, the term has usually been defined in of two ways;

(a) a generic term relating to present status of a unit of range in terms of specific values or potentials, or (b) the present state of vegetation of a range site in relation to the climax (natural potential) plant community for that site.

Rest period. The length of time that a specific land area is allowed to rest (remain

ungrazed). Rotation grazing. A generic term applied to moving grazing animals recurrently

from one grazing unit (paddock) to another grazing unit in the same series (group); one of the basic components of grazing systems.

Short-duration to grazing. A rotational grazing system employing high stocking

density. One herd, commonly 5 to 12 paddocks, grazing periods of 3 to 10 days (less commonly 1 to 15), and two to several grazing cycles per year; the common “rotation grazing” of improved pastures but has also been applied to range.

Stocking density. Animal demand per unit area of land at any instant of time (i.e.,

AU/acre or AU/section of land); an animal/area ratio describing the relationship between the number of animals and the corresponding area of land at any instant of time.

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Stocking intensity. A general term referring to animal demand-grazing land area relationship.

Stocking rate. Animal demand (for forage) per unit area of land over a period of

time (i.e., AUM/acre or AUD/acre or their reciprocals); an animal/area ratio describing the relationship between number of animals and the corresponding land area being grazed over a specified period of time.

Trampling. Treading under foot. The damage to plants or soil resulting from the

hoof impact of grazing animals. Ungrazed. The status of grazing land and associated vegetation that is not

grazed by ungulates herbivores. Ungulate. A hoofed animal, including animals, but also horses, tapirs, elephants,

rhinoceroses, and swine. Utilization. The proportion of current year’s forage production (biomass) that is

consumed and/or destroyed by grazing animals; may refer to single plant species or to a portion or all of the vegetation.

Vegetative. (a) Non-reproductive plant part (leaf and stem) in contrast to

reproductive plant parts (flower and seed) in developmental stages of plant growth. (b) Plant development stages prior to sexual reproductive stage.

Voluntary intake. Ad libitum food intake achieved by an animal when an excess

forage or other feedstuff is available for consumption. Yearlong continuous grazing. A grazing method in which continuous grazing is

applied to yearlong grazing lands. 1

Terminology Source: Vallentine J.F.2002. Grazing Management.