Konza LTER – Plant Community Dynamics

Melinda Smith1, David Hartnett2, Sara Baer3, Scott Collins4, Carolyn Ferguson2, Karen Garrett5, Mark

Mayfield2, Gene Towne2

1Department of Ecology & Evolutionary Biology, Yale University2Division of Biology – KSU

3Plant Biology, Southern Illinois University4Department of Biology, University of New Mexico

5Department of Plant Pathology - KSU

Overview

• Highlight major accomplishments during last five years

• Present new research activities that may be incorporated into the LTER VI proposal

Plant Community Dynamics: Metrics

• Richness, diversity (H’), dominance• Qualitative and quantitative changes in

composition over time– Community heterogeneity (dissimilarity)– Time-lag analysis – rate of change

• Turnover of species– Loss – species extinctions– Gain – patterns of invasion, invasibility

Plant community dynamics: Sampling• Permanent sampling transects are replicated at

various topographic positions (n = 4/topo position/watershed) in replicate watersheds subjected to the different fire frequency, fire season, and grazing treatments– Plant species composition (estimated cover of

individual species) is measured in spring and fall in 5 10-m2 circular plots/transect (20 plots/topo position)

• Data collected since 1984, 1993 (seasonal burns)

Since 2002, plant species composition data have been included in at least 9 cross-site comparisons or syntheses.

• Belowground Plot Experiment (1986) – burning, mowing, and nutrients

• Irrigation Transects (1991) – growing season water additions

• Cattle-Bison Comparison (1995) – assess effects of cattle vs. bison

• Dominant Species Removals (1996/2000) – assess long-term response to removal of dominant grasses

• RaMPs (1997) – timing of precipitation, warming

• Fire Reversal Experiment (2001) – fire history and changing fire regimes

• Water and N limitation Experiment (2002) – water and nitrogen limitation

• Phosphorus Plots (2003) – assess relative P and N limitation

• Savanna Convergence Project (2006) – interactions between fire and herbivory in North American and South African grasslands

• Nutrient Network (2007) – multiple resource limitation, bottom-up vstop-down control

Other resources: KSU Herbarium

• NSF-funded project to database label and annotation data for all KSC specimens (Kansas vascular plants are complete).

• Development of a digital KSU Biodiversity Information System (BiodIS)

• Continue to work to enhance the collections through ongoing and targeted collecting

Land UsePractices

ClimateChange

NutrientEnrichment

BiologicalInvasions

Tallgrass Prairie EcosystemsStructureFunction

Biotic Interactions

AlteredHydrology

Land Cover Change/Woody PlantExpansion

AlteredBiogeochemical

Cycles

• Fire• Grazing• Land use history

• Rainfall timing and amount

• Temperature

• Elevated N deposition

• Fertilization

• Exotic species introductions

Plant community dynamics are relevant to many contemporary global change issues…

Dominant species –Account for a large fraction of biomass and energy flow

Rel

ativ

e fre

quen

cy

0.0

0.2

0.4

0.6

0.8

1.0

Species rank0 5 10 15 20 25 30 35 40 45

Species rank1 2-8 9-48A

vera

ge b

iom

ass

(g m

-2)

0

100

200

300

400

Andropogon gerardii

Uncommon and rare species – account for a large fraction of richness

Smith & Knapp 2003

Fire and grazing as drivers of plant community dynamics

• Historically important, key components of land use

• Considerations:– Fire regime – frequency and timing of fires– Type of grazer – native vs. domesticated

Fire and grazing

Frequent fire

Increases dominance by C4 grasses

Reduces diversity

Decreases dominance by C4 grasses

Increases diversityGrazing

Long-term dynamics

Need to move beyond patterns of change to implications for ecosystem function

Year1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

Pla

nt s

peci

es ri

chne

ss

20

30

40

50

60

70Year of fire Year of fire

Year of fire

Year ofwildfire

Year ofwildfire

010203040506070

Pre-fire Fire Post-fire

Plan

t spe

cies

richn

essAnnually burned

Long-term unburned4-yr burned

Year of fire

Rainfall ManipulationPlots Experiment

Even

t fre

quen

cy, s

ize,

inte

rval

0

10

20

30

40

50

Rainfall events (#/season)

Rainfall size (mm)

Interval between events (days)

AmbientAltered

Ambient

AmbientAltered

Altered

• Average soil water content in top 30 cm reduced by 12%. • Variability in soil moisture increased by 27%.• Soil temperature increased by 1.4 °C

Impacts on plant species diversity

ANPP (g m-2)

500 600 700 800Ambient Altered

1.0

1.2

1.4

1.6

1.8

Variability in soil water content (%wv)

4.0 6.0 8.0 10.0

Div

ersi

ty (H

')

1.5

1.6

1.7

1.8

1.9

2.0

r2 = 0.45P = 0.004

r2 = 0.40P = 0.008

P = 0.04

Knapp et al. 2002

Grass p = 0.05A

NPP

(g m

-2)

100

200

300

400

500

600

Ambienttiming

Alteredtiming

0

50

100

150

200

250

300 A. gerardii p = 0.38S. nutans p = 0.02

Differential species responses

Andropogon gerardii Sorghastrum nutans

Dominant C4 grasses

Fay et al. 2003

Treatment

Amb-C Amb-H Alt-C Alt-H

Andr

opog

on re

lativ

e co

ver (

%)

10

15

20

25

30

35

40

Treatment

Amb-C Amb-H Alt-C Alt-H

Sorg

hast

rum

rela

tive

cove

r (%

)

10

15

20

25

30

35

40Rainfall: P = 0.03Heat: NSRainfall*Heat: NS

Rainfall: NSHeat: P = 0.03Rainfall*Heat: NS

40

Amb-C Amb-H Alt-C Alt-H

Ric

hnes

s

16

18

20

22

24

26

28

30

Rainfall: P < 0.001Heat: P = 0.04Rainfall*Heat: NS

Amb-C Amb-H Alt-C Alt-H

Div

ersi

ty

1.6

1.8

2.0

2.2

2.4

2.6

Rainfall: P = 0.01Heat: P = 0.01Rainfall*Heat: NS

Effects of warming of community diversity

Differential species responses: Flowering

A. gerardii

0.0

0.2

0.4

0.6

0.8

1.0

1.2

bbsm2 bbsm2: 0.8125 bbsm2: 0.7500

S. nutans

Flow

erin

g st

ems

per m

2

0.0

1.0

2.0

3.0

4.0

5.0ControlWarmed

Ambient Altered

Andropogon more sensitive to warming

Sorghastrum more sensitive to water availability

What are the mechanisms underlying differential sensitivity?

Genotypic constraints

Geneexpression

Phenotypic effect on physiology

GeneticGenetic

Tallgrass Prairie Tallgrass Prairie Community & Ecosystem Community & Ecosystem

ResponsesResponses

EcologicalEcological

Dominant speciesDominant speciesresponsesresponses

ClimateChange

• Rainfall timing and amount

• Temperature

Linking responses across scales

Hierarchical Ecosystem Response Model

Smith, Knapp and Collins, in prep

Ecos

yste

m re

spon

se (+

/-)

Time

Press resource alteration

Invasive species

a) Physiological response

c) Immigration(new species)

b) Speciesre-ordering

Linking genetics to ecosystem responses

CarbonRelations

EnvironmentalDrivers

Water availabilityTemperature

Genes

IndividualPerformance

(growth)

Leaf-level Individual

Water Relations

CarbonRelations

Genes

IndividualPerformance

(growth)

Water Relations

PopulationPerformance Community

Diversity

EcosystemFunction(ANPP)

Community/Ecosystem

Population

Sorghastrumnutans

Andropogongerardii

PopulationPerformance

What is the genetic basis for ecosystem responses to altered climate?

Where do we go from here?

Year1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

Pla

nt s

peci

es ri

chne

ss

20

30

40

50

60

70Year of fire Year of fire

Year of fire

Year ofwildfire

Year ofwildfire

010203040506070

Pre-fire Fire Post-firePl

ant s

peci

esric

hnes

sAnnually burnedLong-term unburned4-yr burned

Year of fire

Why a new approach to assessing community change should be considered…

After 8 yrs, aboveground production still remains ~30% lower than controls!

Why?

Andro Sorg Other Forbs

Abov

egro

und

prod

uctiv

ity (g

m-2

)

0

100

200

300

400

Control100% Removal

P < 0.001

P = 0.04

0% 100%

Abov

egro

und

prod

uctiv

ity (g

m-2

)

0

100

200

300

400

500

600

700P < 0.001

In 1996, 100% of A. gerardii and S. nutans were removed from 8 plots- Resampled 8 years later

Relative cover data suggested compensation

Additional recommendations

• Take advantage of existing data from long-term experiments to assess how changes in abundance of dominant species influence community change

• Targeted, more comprehensive sampling of existing manipulations– Resample long-term dominant species removal

experiments– Nutrient manipulation experiments, etc…

Integrate across scales• Broaden our definition of plant community

diversity to include other levels of diversity –e.g., genetic (of dominant species), pathogen, microbial– Assess change in genetic diversity of dominant

species in response to long-term manipulations– Consider archiving samples for measuring genetic

diversity

• Linkage of dynamics across hierarchical scales

• Explicitly include physiology-population-community linkages in ongoing research