198516932034341391 199440901874211420 200175671904161389 198745281650280812099...
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1985 16 93 203 434 1391
1994 40 90 187 421 1420
2001 75 67 190 416 1389
1987 45 281 650 2808 12099
1996 149 246 1509 2764 11215
Ejidos-Quintana Roo, East Scene (Area in km2) total area: 2,138 km2
YearBracken
FernAgricult.
Secondary Vegetation
Lowland Forest
Upland Forest
Ejidos-Campeche West Scene (Area in km2) total area: 15,885 km2
YearBracken
FernAgricult.
Secondary Vegetation
Lowland Forest
Upland Forest
2001 175 228 1160 2637 11689
Plant Invasions in an Agricultural Frontier: The case of bracken fern invasion in southern Yucatán Peninsular region.
Laura C. SchneiderDepartment of Geography-SYPR Project
Rutgers University
Acknowledgements: This poster is supported by the Southern Yucatán Peninsular Region (SYPR) project involving Clark University, University of Virginia, El Colegio de la Frontera Sur, and Harvard University. Its principal sponsors have been NASA-LCLUC (Land Cover and Land Use Change) program (NAG5-6046, NAG5-11134, and NNG06GD98G), Center for Integrated Studies of the Human Dimensions of Global Environmental Change, Carnegie Mellon University (NSF SBR 95-21914), and NSF-Biocomplexity (BCS-0410016).
Land Change in Southern Yucatán Peninsular Region
Ejidos/Agricultural based community
Study Region (Ejidos) Calakmul Biosphere Reserve
40 km
Calakmul Biosphere Reserve Archaeological tourism
LCLUC-SYPR
(Adapted from Roy Chowdhury and Schneider, 2004)
Deforestation hotspots from 1987-1997
Landscape Mosaic
Land Cover in SYPR
Maize Cultivation
Cash Crop: Jalapeño peppers.
Secondary Growth
Invasive species
Biological invasions are widely recognized as a serious threat to environments, economies and human welfare throughout the world. The large scale of some biotic invasions and the impact and ineffective policies and practices to prevent or control them, have made biological invasions one of the major factors that constitute global change. Research on biotic invasions, however, remains limited to trying to understand the human-environment relationships that give rise to those invasions, especially in tropical regions.
Remote sensing analysis shows that approximately 3.8% of forest (mainly upland forest) has been lost from 1987 to 1997. West and East regions where part of the oil boom sponsored “development programs” in the 1970s and early 1980s (e.g. cattle ranching and rice projects). Reforestation can be seen more conspicuity in those areas as well. South deforestation rates are the highest, mainly due to increase in cash crops (e.g. peppers)
Currently, the dominant land tenure system is the ejido: communally managed land granted by the Mexican government. The main activity of farmers is subsistence agriculture, but recently there has been an increase in commercial cultivation of hot peppers. These and other land pressures pose various problems in concert with the needs of the conservation and archeo-tourism programs for maintenance of mature forest in the region and for lessened demands on remaining forest on ejido lands.
Bracken Fern (Pteridium Aquilinium) Invasion
1985 15 km2 1994 40 km2
2001 75 km2
Regional (years)
Local (days)
Upland ForestBracken Fern
Ecological Impacts•“Arrested” succession (Patches up to 25 years old)• Increase of fire frequencies• Decrease in biodiversity• Changes on soil nutrients
Bracken Fern in the region is usually located close to main roads and settlement areas, but it could also be found in the areas more difficult to access and in areas surrounded by forest. The main strategies for bracken to flourish and disperse are: high resistance to diseases and pests, the presence of allelopathic substances, vegetative reproduction, the high density of the frond canopy and litter suppressing the ground flora, and tolerance to a broad range of climatic and edaphic conditions. Another factor contributing to bracken fern invasion is the resistance of the rhizome to fire and adverse weather conditions, allowing the colony to spread vegetatively. Swidden agriculture is the main type of land management in the region and fires are critical in the configuration of bracken fern distribution in the landscape.
Patterns of bracken fern invasion
Linkages of Land Management Practices and Bracken Fern Invasion
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
Forestry Extensions Calakmul Reserve Agricultural Ejidos Private Land
pe
rce
nta
ge
of
bra
ck
en
fe
rn o
f to
tal a
rea
1987
2001
70% of 1, 80% of 2: attempt agriculture in fern areas
Ejido 1 w/ fern (n=24)
Ejido 1 w/o fern (n=8)
Ejido 2 w/ fern (n=10)
Ejido 2 w/o fern (n=10)
Average fern plot (ha)
19 N/A 4 N/A
Average plot in agriculture (ha)
3 5 2 4
Maize yields in bracken area (kg/ha)
250 N/A 120 N/A
Maize yields in agricultural areas
650 750 700 1100
# days/ha weeding 6 4 6 9
Average fallow cycle
2:6 2:5 2:4 2:4
EJIDO 2Wetland Forest (Bajos)Upland ForestSecondary growthAgricultureBracken FernInundated Savannas
EJIDO 1
0
20
40
60
80
100
120
140
160
3 years 1 year least than 1year
2-5 yearssecondaryvegetation
Mature Forest
Ab
ove
gro
un
d b
iom
ass
(Mg
/ha)
0
5
10
15
20
25
30
35
40
3 years 1 year least than 1year
2-5 yearssecondaryvegetation
Mature Forest
Flo
or
bio
mas
s (M
g/h
a)
(a) Above ground biomass (b) Biomass floor (litter)
Less than 15 years (n=8) More than 15 years (n=10) p-value
pH 7.81 ± 0.08 7.88 ± 0.16 0.263
Organic Matter 8.95 ± 1.30 9.08 ± 1.53 0.846
Est. Nitrogen Release 118 ± 4.95 119 ± 6.86 0.744
P_ppm 19.31 ± 10.6 11.8 ± 4.65 0.0610*
Ca_ppm 13495 ± 2576 11521 ± 3481 0.201
Mg_ppm 330 ± 59 290 ± 74 0.231
K_ppm 577 ± 229 515 ± 132 0.484
Na_ppm 28.44 ± 3.32 25.7 ± 2.64 0.0690*
B_ppm 1.56 ± 0.22 1.24 ± 0.14 0.0016*
Fe_ppm 17.06 ± 5.51 21.1 ± 8.73 0.273
Mn_ppm 86.2 ±47.8 98.5 ± 84.5 0.719
Cu_ppm 4.80 ± 1.26 4.25 ± 2.11 0.531
Zn_ppm 2.15 ± 0.38 1.74 ± 0.81 0.219
Al_ppm 106.7 ±61 179.7 ± 115 0.126
Conceptual Model of Bracken Fern Invasion in the Southern Yucatán
Weeding, fire control(unstable)
Smaller plots, shadow, lack fire, closer distance to forested areas, cutting and weeding
Land clearing: human or environmentally driven
Upland Forest-Secondary Vegetation
Agriculture (milpa), pasture, agro-forestry, hot peppers
Succession
Abandonment/areas closer to bracken fern plots; northeast facing slopes
Bracken Fern
Fire
Increase in Bracken Fern biomass, size of plots, and flammability. Decreasein P, increase in Al.
Land clearing, change soil nutrients: short term increases in fertility
Eradication of bracken by manual labor
Land Tenure
At least four types of land tenure exist in the region: ejido land (largely usufruct), private land (largely ranches), forest extensions (ampliaciones) and National Land, the latter assigned exclusively to the Calakmul Biosphere Reserve. Private lands have the highest density and largest increase of bracken fern areas, followed by ejido land; bracken fern is almost absent in forest extensions and in the Calakmul Biosphere Reserve. This result is expected because the invasive species requires land clearing and frequent fires to establish itself; those disturbances are mainly driven by human activities taking place in ejidos and on ranches.
The two ejidos examined here were selected using information on fern density derived from 1997 satellite data. The selected ejidos represent high density (ejido 1) and low density (ejido 2) of fern invasion respectively. A stratified random sample of 46 farmers in the two villages was selected for interview; the interviews were conducted between January and June 2002. The land-use history and current land conditions of these two case-study ejidos may be contrasted. One, a relatively new ejido characterized by high land pressures, strong involvement in cropping, has the highest percentage of forest and lowest percentage of bracken fern areas. The oldest ejido characterized by low land pressures and a more recent disinvestment in cropping, has the highest percentage of bracken fern invasion.
(Adapted from Schneider and Geoghegan, 2006) Results of modeling suggest that farmers with smaller land holdings, specifically with smaller amounts of remaining forest, were less likely to abandon invaded areas. Also, the influence on the wage rate, proxied via the education variable, demonstrated that farmers with greater off-farm labor options were more likely to abandon an invaded plot. Finally, potentially important policy-relevant results from this study indicate that farmers who keep their agricultural plots in continuous production for longer periods are less likely to abandon these plots after invasion.
Modeling land abandonment and bracken fern invasion
As many governmental and non-governmental organizations are involved with trying to reduce deforestation in the region to help protect biodiversity and other ecological goods associated with the Calakmul Biosphere Reserve, any policy designed to affect land use decisions in the region must take into consideration the impact on the spread of bracken fern and the response of farmers to the invasion.
Ecological mechanisms of bracken fern invasion
Fire regime Fire regime
Soil Nutrients in bracken fern fields of different length (years) of invasion
Above ground biomass and biomass floor for bracken fern in plots of eastern ejidos differentiated by the last time they burnt. Also, the same values are shown for 2-5 year secondary growth and Mature forest in the region (data taken from Lawrence and Foster, 2002)
The above results indicate an increase in floor biomass by bracken fern individuals the longer the period without fires. Bracken fern floor biomass is prone to fires, and, through this strategy of promoting fire, it is very rare that a large invaded parcel (more than 10 ha) does not burn on a yearly basis. It is also important to notice that allelopathic substances are produced by bracken fern litter, which could limit the growth of other colonizers.
To evaluate the effect of length of bracken fern establishment on soils, the samples were divided in two groups: plots that have been established for 15 years or more, and plots established between 5 and 15 years. The nutrient showing the highest statistically significant difference between the two groups is P. The result indicates a lower concentration of P in soils that have supported bracken fern for longer periods of time. There is also a lower concentration of B and K but higher levels of Al.
The results indicate some of the long-term effects of invaded areas on soil nutrients: decrease in P, Na and B. Nitrogen levels do not seem to be affected by the invasion. A nutrient that limits growth in the vegetation in the region is P — a decrease in P could make it more difficult for secondary vegetation to compete successfully with bracken fern. The increase of toxic elements such as Al and Cu could have similar impacts.
5 km2 km
(Schneider, 2006; JLAG)
Contact Information:Laura [email protected]