Ecosystem resilience and renewable resource management: A mathematical bioeconomic analysis of shifting cultivation in tropical forests.

摘要

Economists and policy analysts have long studied the role of shifting cultivation in economic development. Most recently, concern about tropical deforestation has motivated a debate about the economic efficiency and ecological viability of shifting cultivation practices. Many governments and NGOs have responded by developing policies and programs that aim to increase agricultural intensity and economic output in order to improve welfare and slow deforestation.;Recent economic models of shifting cultivation that consider the dynamics of soil fertility over the farming cycle assume that fertility recovers during the fallow, but do not account for the role of biomass growth in the recovery process. As a result they cannot consider the impact of cropping activities on the natural processes that support fertility recovery.;The work presented here extends these soil fertility models by incorporating a model of interdependent resources to represent explicitly the dependence of fertility regeneration on biomass vegetation. A multidimensional mathematical bioeconomic model of optimal cultivation is developed and the concept of recuperative potential is formalized. The mathematical model includes consideration of discontinuous irreversible environmental degradation due to overcropping. A simple Lotka-Volterra model of competitive exclusion illustrates how cropping activities can lead to discontinuous change in the dynamics of fertility recovery.;Most generally, shifting cultivation is represented as the management of an economically valuable renewable resource where use of that resource not only leads to its own depletion but also degrades the means by which the resource is renewed. The impact of resource use on resource renewal can be of tremendous importance to the sustainability of shifting cultivation, fisheries, and other resource management systems and yet receives almost no attention in the natural resource economic literature.;Policy analysis reveals possible unintended consequences of policies that aim to improve long term welfare by agricultural intensification. By incorporating the ecological basis for soil fertility regeneration, the model identifies the possibilities of ecological and economic losses from policies that encourage longer cropping periods. In contrast, there are ecological and economic benefits from conservation of system recuperative potential through fallow management.