RATES AND PATTERNS OF DEFORESTATION IN THE PHILIPPINES - APPLICATION OF GEOGRAPHIC INFORMATION-SYSTEM ANALYSIS

Land-use maps for 1934 and 1988, and a 1941 road map of the Philippines were digitized into a geographic information system. These maps were then analyzed to determine the rates of deforestation and their relationship with factors such as the distance of forests to roads and forest fragmentation (measured by perimeter-to-area ratio (P/A ratio) of forest patches) for this country. The Philippines lost a total of 9.8 million ha of forests from 1934 to 1988.The presence of major roads was a very important factor affecting deforestation. The closer a forest was to roads, the higher the rate of deforestation. Nearly 78% of the 2.1 million ha of forests within 1.5 km of roads in 1934 was removed by 1988. By contrast, only 39.5% of forest was lost between 15.0 and 16.5 km from roads. The density of roads per unit area did not predict deforestation as well as the distance of forest patches to roads. The P/A ratio of forest patches was also useful for assessing their rate of clearing. The larger the P/A ratio of a forest patch, the more likely it was to be cleared. Forests with P/A ratios greater than 65 m ha-1 in 1934 had all disappeared by 1988. Forests with large P/A ratios were also characterized by small area and the presence of adjacent agricultural lands in 1934. They were readily cleared and never reforested.