1985

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]