GLOBAL TROPICAL FOREST AREA MEASUREMENTS DERIVED FROM COARSE RESOLUTION SATELLITE IMAGERY - A COMPARISON WITH OTHER APPROACHES

Definition of appropriate tropical forest policies must be supported b y better information about forest distribution. New information techno logies make possible the development of advanced systems which can acc urately report on tropical forest area issues. The European Commission TREES (Tropical Ecosystem Environment observation by Satellite) proje ct has produced a consistent map of the humid tropical forest cover ba sed on 1 km resolution satellite data. This base-line reference inform ation can be further calibrated using a sample of high-resolution data , in order to produce accurate forest area estimates. There is good ge neral agreement with other pantropical inventories (Food & Agriculture Organization of the United Nations Forest Resources Assessment 90, Wo rld Conservation Union Conservation Atlas of Tropical Forests, Nationa l Aeronautics & Space Administration [USA] Landsat Pathfinder) using d ifferent approaches (compilation of existing data, statistical samplin g, exhaustive survey with satellite data). However, for some countries , large differences appear among the assessments. Discrepancies arisin g from this comparison are here analysed in terms of limitations assoc iated with each approach and they are generally associated with differ ences in forest definition, data source and processing methodology. Ac cording to the different inventories, the total area of closed tropica l forest is estimated at 1090-1220 million hectares with the following continental distribution: 185-215 million hectares in Africa, 235-275 million hectares in Asia, and 670-730 million hectares in Latin Ameri ca. A proposal for improving the current state of forest statistics by combining the contribution of the various methods under review is mad e.