Data about the world’s forest cover is an important prerequisite for global environmental change research, from studies on biodiversity and effective conservation to modeling sustainability of forest ecosystems. Expanding on the recently completed U.S. Geological Survey (USGS) global land cover characteristics database, USGS EROS Data Center is producing a global forest cover map for the United Nations Food and Agriculture Organization (FAO). Broad, discrete forest-canopy cover categories are mapped at 1-km resolution for use by FAO’s year 2000 Forest Resource Assessment project. Seasonal land cover classes from the USGS database are optimized and adapted to FAO definitions using combinations of remapping, clustering, and linear unmixing techniques. Preliminary forest cover maps have been produced for several continents. Results show that the basic objectives of forest cover mapping and linkage to the USGS database can be met adequately with the methodology.1
The United Nations Food and Agriculture Organization (FAO) conducts periodic forest resource assessment at the global scale (FAO, 1993). The current forest resource assessment for the reference year 2000 (FRA2000) is being conducted to estimate forest area, forest conditions, and the rate of change in a number of important parameters (e.g. area, forest type). In addition to collecting country survey reports and sampling high-resolution satellite scenes, FRA2000 will also, for the first time in its survey history, feature a global forest cover map produced at 1-km spatial resolution. The global forest cover map is being produced at the U.S. Geological Survey (USGS) EROS Data Center (EDC) in cooperation with FAO.
There have been well-conducted studies to map forest cover at the regional or continental extent, such as the TREES study (Malingreau et al. 1995) and the Humid Tropical Landsat Pathfinder study (Skole and Tucker, 1993). These studies provide significant opportunities for regional applications, but the studies are limited in scope for a global forest cover map. On the other hand, the recently completed USGS global land cover database (Loveland et al., in press) represents a complete global coverage produced with a consistent methodology and a flexible database philosophy, using Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) as the primary input data. Two levels of land cover are available from the database: the full classification based on seasonal definitions and the aggregated 17-category International Geosphere and Biosphere Programme (IGBP) classification (Loveland et al., in press). The USGS database is being used for a broad range of earth science applications, from land cover mapping to biological conservation (Reed, 1997). The FAO forest cover mapping effort builds on the full USGS seasonal database, refining forest classes to reflect forest density classification.
The global forest cover map may be used by the FAO FRA2000 project to provide spatial definition to area statistics of survey findings. As a complete enumeration of forest cover in the world, the map is an additional data source and may be used to supplement regions lacking recent, reliable forest inventory (FAO, 1995). As a new addition to the USGS land cover database, the effort should help improve applications of the database when information about forest cover is needed.
1 The work presented here has been carried out by Zhiliang Zhu and Eric Waller, EROS Data Centre, USA (under U.S. Geological Survey contract 1434-CR-97-CN-40274), through a Letter of Agreement with FAO-FRA.