|Traditional slash and burn farming involves cutting all or most of the trees on small (<2-3 ha) forest plots, burning the slash to release nutrients into the soil and remove existing vegetation, cultivating the plots for 1-3 years, and then abandoning the plots as soil nutrients are depleted and weeds overtake the field. The plot, termed a milpa throughout this paper, is left fallow, and the regenerating vegetation helps to improve soil structure and chemistry. While most tropical soils are poorly suited for agriculture, shifting cultivation can be productive and sustainable in areas where low population densities are present. Today, however, longer cultivation periods followed by shorter fallow periods are common in many tropical areas due to demographic pressures and economic incentives. These changes in the shifting cultivation cycle can degrade the soil's physical structure, result in lower soil nutrient content as plots fail to recover fully between cropping cycles, and alter soil biological dynamics.
In addition to changes in the intensity of cropping in many shifting cultivation areas, increasing populations and improved transportation infrastructures have led to an increase in the amount of land put into cultivation, resulting in the loss of primary and secondary forests as they are converted to farmland and pasture. Habitat fragmentation associated with agricultural expansion results in greater distances between milpas and mature forests, which may affect species composition and recovery.
Given that the foresteded matrix which has long dominated tropical areas is being replaced by an agricultural matrix, we believe that it is important to clarify how such changes affect ecosystem structure and function. In this research, we specifically addressed the question of whether increased distance from older forest affects species composition and regrowth on abandoned milpas. We hypothesized that vegetation characteristics would differ not only between milpas at different stages in their rotation (in use vs. fallow) but also between milpas located at near (<100 m) and far (>100 m) distances from older forest. To this end, we compared four plant community measures - species composition, diversity, life form dominance, and woody biomass - among milpas varying in their age and distance to older forest.
|A Mayan mound in the Lamanai Archeological Reserve. This reserve houses the most in-tact forest of the area. The forest is seasonal dry tropical, except along the New River Lagoon, baja.|
|Our research involved examining the composition and structure of milpas of various age and distance from an older (>50 years) forest, as well as soil nutrient analyses. Dr. John Kupfer (U. South Carolina) is a PI on this work.|
|Milpa with last seasnon's corn and this year's beans. Notice older forest in the background.|
|Lush undergrowth of the forest. The forest is being sampled as well as the milpas to provide some reference on species and soil characteristics.|
|Lamanai Field Research Center|
|Publications from this research:
Amy Webbeking. 2000. The spatio-temporal variance of milpa vegetation recovery in Belize. MS Thesis, University of Memphis, TN.
Kupfer, John A., Amy Webbeking & Scott B. Franklin. 2004. Landscape fragmentation affects vegetation recovery in Belize , C.A. Agriculture, Ecosystems and Environment 103:509-518.