Satellite-based studies indicate that land cover change in the PRC is occurring at unprecedented rates. A recent remote sensing analysis by Seto (2000) showed that between 1988 and 1996, urban land areas in the greater Pearl River Delta region in the southern PRC increased by over 300%, while natural and agricultural land declined by approximately 6% and 10%, respectively (Fig. 2). How have these changes affected the terrestrial carbon cycle in the region? To answer this question, we employed satellite remote sensing, ecosystem process modeling, and ecological data to investigate the effects of the land cover change on two components of the carbon cycle: net primary production (NPP) and ecosystem carbon storage (Dye et al., 2002).

Figure 2 Major land cover classes in the Pearl River Delta region. Locations of land cover change during 1988 to 1996 are depicted in yellow color. These changes have resulted in a net release of carbon to the atmosphere.

These images depict the city of Shenzhen in the Pearl River Delta as observed by the Landsat TMsatellite sensor in 1988 (top) and 1996 (bottom).   Green vegetation is indicated by red color and urban areas are indicated by yellow color. Rapid urbanization associated with economic development has removed vegetation from the landscape, causing a net loss of carbon stored in the region's terrestrial ecosystems.

The results from our analysis suggest that land cover change in the Pearl River Delta region between 1988 and 1996 affected the regional carbon cycle by reducing both the annual rate of NPP and the size of the terrestrial carbon pool. The dominant mode of land use change was the conversion of natural and agricultural land to urban uses. Urbanization generally involves the removal of vegetation (forests, grassland, or agricultural crops) and replacing it with roads, buildings, and other urban infrastructure. As a consequence of the urbanization, the annual amount of atmospheric carbon assimilated into vegetation through NPP declined by approximately 1.5 Megatons (-7.5%). This result indicates a reduction in the total photosynthetic capacity and carbon sequestration potential of the region's ecosystems. More than half (55%) of this reduction in NPP is attributable to the loss of agricultural land. The urbanization released about 12 Megatons carbon from the terrestrial carbon storage pool, of which 19% was from soils and 81% from vegetation. This amount of carbon released is about 13% the estimated annual amount of carbon released by fossil fuel combustion in the Pearl River Delta region. Because urbanization is the dominant type of change, there is low potential for the ecosystems to recapture the lost carbon through vegetation regrowth. Thus, land cover change is responsible for a sustained reduction in the size of the terrestrial carbon pool in the Pearl River Delta region.

The future course of the socioeconomic driving forces that influence land cover change in the PRC, in combination with potential climate change, will determine whether these effects on the region's carbon cycle become exacerbated or diminished in the coming decades.