Humid tropical forest clearing from 2000 to 2005 quantified by using multitemporal and multiresolution remotely sensed data

Abstract

Forest cover is an important input variable for assessing changes to carbon stocks, climate and hydrological systems, biodiversity richness, and other sustainability science disciplines. Despite incremental improvements in our ability to quantify rates of forest clearing, there is still no definitive understanding on global trends. Without timely and accurate forest monitoring methods, policy responses will be uninformed concerning the most basic facts of forest cover change. Results of a feasible and cost-effective monitoring strategy are presented that enable timely, precise, and internally consistent estimates of forest clearing within the humid tropics. A probability-based sampling approach that synergistically employs low and high spatial resolution satellite datasets was used to quantify humid tropical forest clearing from 2000 to 2005. Forest clearing is estimated to be 1.39% (SE 0.084%) of the total biome area. This translates to an estimated forest area cleared of 27.2 million hectares (SE 2.28 million hectares), and represents a 2.36% reduction in area of humid tropical forest. Fifty-five percent of total biome clearing occurs within only 6% of the biome area, emphasizing the presence of forest clearing "hotspots." Forest loss in Brazil accounts for 47.8% of total biome clearing, nearly four times that of the next highest country, Indonesia, which accounts for 12.8%. Over three-fifths of clearing occurs in Latin America and over one-third in Asia. Africa contributes 5.4% to the estimated loss of humid tropical forest cover, reflecting the absence of current agro-industrial scale clearing in humid tropical Africa.

Fig. 1.

Forest clearing and forest cover in the humid tropical forest biome, 2000–2005. Total forest clearing over the study period is estimated to be 27.2 million hectares (SE 2.28 million hectares). Regional variation in clearing intensity is shown: Region 1 covers 6% of the biome and contains 55% of clearing; region 2 covers 44% of the biome and contains 40% of forest clearing; and region 3 covers 50% of the biome and contains 5% of forest clearing. Data from this figure are available at http://globalmonitoring.sdstate.edu/projects/gfm.

Fig. 2.

Examples of Landsat sample blocks characterized to estimate forest cover and change from 2000 to 2005. Each block covers 18.532 km per side and has been reprojected into local Universal Transverse Mercator coordinates. The strata are created by using the biome-wide MODIS 2000 to 2005 forest clearing probability maps. (a) Sample block from the MODIS change strata 1 and 5. (b) Sample block from MODIS change strata 2 and 6. (c) Sample block from MODIS change strata 3 and 7. (d) Sample block from MODIS change certainty strata 4 and 8. All blocks used in this analysis can be viewed at http://globalmonitoring.sdstate.edu/projects/gfm.

Fig. 3.

Landsat and MODIS change comparison for the 183 sample blocks analyzed.