Georg-August-Universität Göttingen, Department of Landscape Ecology, Germany
Despite the existence of international resource protection programs since the UNCED conference 1992 in Rio de Janeiro (AGENDA 21), rainforest conversion by non sustainable forest use as well as agricultural colonisation accompanied by clearcutting continues. Partly low fertile soils as well as fertile soils due to inappropriate use (p.e. mechanised cropping) led also in the Inner Tropics to a high portion of degraded soils.
Based on project studies in Ecuador/Bolivia (Amazon basin and submontane rainforests), West Africa (Rainforest and cocoa-systems) and Indonesia (lowland rainforest Central Sulawesi), consequences of clearcutting, annual cropping and agroforestry (cocoa) on soil and water nutrient cycling are presented. These researchs show that differing processes and budgets lead to soil degradation of varying reversibility. Depending on precipitation amount and soil nutrient status, annual cultures and pastures have significantly higher seepage nutrient losses than agroforestry systems (cocoa, coffee). Litterfall plays a more important role for soil nutrient supply than throughfall. By establishing agroforestry systems, nutrient enriched throughfall and litterfall can be used for the rehabilitation of degraded soils. The comparison between cocoa- and citrus agroforestry systems and monocultures on Ultisols in Bolivia illustrates the differing development of soil nutrient status and points out the potential for sustainable land use even on nutrient impoverished soils after 30 years of slash & burn agriculture.
Project results from the eastern lowlands of Bolivia are used to develop a GIS-based methodology to identify potential landscape changes on a regional scale, including potential deforestation areas as well as areas with a high probability of soil degradation. The system development is based on the principles of the scenario formation and uses particularly fuzzy logic methods. The conversion of forest areas since 25 years (change detection), soil- and climate data and parameters related to people-environment interactions (driving forces) are used for practical decision rules. The results serves as an example for decision support in regional land use planning and to identify risk areas of soil degradation.
Keywords: GIS based analysis, Ivory Coast, land use, tropical rainforest, nutrient cycling, soil degradation, soil rehabilitation, soil nutrient status