1985

1. Ejidos-Quintana Roo, East Scene (Area in km2) total area: 2,138 km2 Year Bracken Fern Agricult. Secondary Vegetation Lowland Forest Upland Forest 1985 16 93 203 434 1391 1994 40 90 187 421 1420 2001 75 67 190 416 1389 Ejidos-Campeche West Scene (Area in km2) total area: 15,885 km2 LCLUC-SYPR Year Bracken Fern Agricult. Secondary Vegetation Lowland Forest Upland Forest Local (days) 1987 45 281 650 2808 12099 1996 149 246 1509 2764 11215 2001 175 228 1160 2637 11689 Wetland Forest (Bajos) Upland Forest Secondary growth Agriculture Bracken Fern Inundated Savannas Plant Invasions in an Agricultural Frontier: The case of bracken fern invasion in southern Yucatán Peninsular region. Laura C. Schneider Department of Geography-SYPR Project Rutgers University Land Change in Southern Yucatán Peninsular Region Bracken Fern (Pteridium Aquilinium) Invasion 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. Study Region (Ejidos) Calakmul Biosphere Reserve Deforestation hotspots from 1987-1997 Patterns of bracken fern invasion Regional (years) • Ecological Impacts • “Arrested” succession (Patches up to 25 years old) • Increase of fire frequencies • Decrease in biodiversity • Changes on soil nutrients 1994 40 km2 2001  75 km2 1985  15 km2 40 km Upland Forest Bracken Fern Calakmul Biosphere Reserve Archaeological tourism Ejidos/Agricultural based community (Adapted from Roy Chowdhury and Schneider, 2004) 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 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. Land Cover in SYPR Landscape Mosaic Secondary Growth Cash Crop: Jalapeño peppers. Maize Cultivation Invasive species Linkages of Land Management Practices and Bracken Fern Invasion EJIDO 1 EJIDO 2 Eradication of bracken by manual labor 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. 2 km 5 km Modeling land abandonment and bracken fern invasion 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. Land Tenure (Schneider, 2006; JLAG) Ecological mechanisms of bracken fern invasion Conceptual Model of Bracken Fern Invasion in the Southern Yucatán (a) Above ground biomass (b) Biomass floor (litter) Succession 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. Upland Forest- Secondary Vegetation Land clearing: human or environmentally driven Agriculture (milpa), pasture, agro-forestry, hot peppers Abandonment/areas closer to bracken fern plots; northeast facing slopes Smaller plots, shadow, lack fire, closer distance to forested areas, cutting and weeding Fire Weeding, fire control (unstable) Increase in Bracken Fern biomass, size of plots, and flammability. Decrease in P, increase in Al. Fire regime Fire regime Land clearing, change soil nutrients: short term increases in fertility 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) Bracken Fern Soil Nutrients in bracken fern fields of different length (years) of invasion 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. 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. 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).  Contact Information: Laura C.Schneider laschnei@rci.rutgers.edu