Homeostasis and Degradation in Fragile Tropical Agroecosystems

When both people and their natural environment are "at the margin," small changes in the natural resource base often have important effects on peoples lives. Conversely, modifications in human activities may significantly affect ecosystem functioning. This responsiveness makes it necessary to study the interactions between human behavior, natural capital stocks, and the flow of ecosystem services. Farmers make many decisions about land use and improvement, selection of crop varieties, livestock-management strategies, chemical applications, and labor allocation. These decisions fundamentally affect the growth of plants, livestock, and soil biology -- in short, the functioning of the entire agroecosystem. Complex feedback loops send responses to the different subsystems engendering dynamic reactions. Exogenous shocks, such as those associated with climate variability and changing economic incentives, regularly disrupt processes in this complex system. Over time, those disturbances propagate throughout the system, causing adaptation in behaviors and performance of the subsystems. Understanding the interplay between smallholder farmers in Kenya and their natural environment is the primary goal of this project. Within three Kenyan research sites, Embu in the central highlands, Siaya-Vihiga in the Lake Victoria basin in subhumid western Kenya, and upper Baringo in the Rift valley, some farmers have adapted their agricultural practices to sustain their soils through crop-livestock integration and use of a variety of conservation strategies. Within the same ecosystem, some farmers are able to maintain soil fertility and farm productivity, while their neighbors are caught in "natural resource poverty traps" that yield food insecurity and agroecosystem degradation. Studies of the systems that are able to maintain homeostasis as well as those that do not recover from human and natural shocks provide the opportunity to understand the central biophysical and socioeconomic processes that underpin agroecosystem functioning in the tropics. The investigators will develop a model using a system dynamics approach that includes the complex feedback loops among economic (conditioned by sociological constraints), livestock, crop, and soils submodels. The model will be calibrated and tested using data on soil status (nutrients, organic matter and microbial profiles), crop yields, plant biomass production, and livestock growth as well as production and socio-economic data. Depletion of soil fertility is increasingly acknowledged to be the fundamental biophysical cause of declining food production in Africa. Unless the causes for soil depletion are remedied, it will be impossible to increase food production to meet projected demand due to population growth and to ensure that the 37 percent of the sub-Saharan Africans receiving less that 2,200 calories per day are adequately nourished. Because this projects research sites vary by ecological zone and market access, they represent systems throughout Africa and much of the developing world. This research project will permit a comprehensive evaluation of socioeconomic and biophysical factors that contribute to degradation of tropical agroecosystems. The project will add to limited understanding of the microbial ecology of tropical soils, and to knowledge about when soils reach thresholds beyond which replenishment is difficult. The project also will contribute to knowledge of the processes through which people become trapped in poverty. The integration of the contributions to individual research areas will be made more useful through integration into a dynamic model that will permit exploration of the responses of these vulnerable systems to economic and biophysical shocks. This project is supported by an award resulting from the FY 2002 special competition in Biocomplexity in the Environment focusing on the Dynamics of Coupled Natural and Human Systems.