The Three Gorges Dam: an ecological perspective

development throughout the world for thousands of years, providing water, controlling floods, irrigating crops, facilitating navigation, creating recreational opportunities, and generating motive power and electricity. By the end of the 20th century, about 45 000 large dams (>15 m in height) and an estimated 800 000 small dams had been built worldwide (WCD 2000), obstructing over 65% of fresh water flow to the oceans (McCully 1996; Nilsson and Berggren 2000). With more than 22 000 large dams (but only 22 before 1949), China is the largest dam-building country; by way of comparison, the country with the second-highest total, the US, has just 6390 (WCD 2000). Until recently, large dams were perceived as a symbol of progress in hydraulic engineering and economic development, but this image has waned steadily in the past several decades in the face of increased recognition of their failure to provide the expected economic benefits, along with heightened awareness of their detrimental effects on the environment (Milliman 1997). Dams have resulted in large-scale habitat fragmentation and ecosystem alterations that adversely affect both terrestrial and aquatic biodiversity (Dynesius and Nilsson 1994; Rosenberg et al. 2000; Terborgh et al. 2001; Wu et al. 2003a,b). Habitat fragmentation involves both a reduction or loss of habitat and a decrease in habitat connectivity. The debate over the world’s largest dam, the Three Gorges Dam (TGD) (Figure 1), highlights many of the controversies relating to dam construction (see Edmonds 1991), but in this case the dam proponents prevailed, and the huge structure is now in place. Many ecologists and other scientists have expressed concern over the environmental consequences of the TGD. How is the TGD affecting the biodiversity and environmental conditions of the region? A thorough assessment of its effects requires adequate information on the composition and spatial distribution of biodiversity before and after dam construction, as well as long-term monitoring. Several field surveys have been published in Chinese since the 1980s (eg CASTGPC 1987; Chen et al. 1994; Yang 1997; Xiao et al. 2000). These studies provide critical, though incomplete, baseline information on the ecological conditions of the region before the dam was constructed and are of tremendous value in assessing the ecological effects of the TGD, now and in the future. The purpose of this paper is not just to summarize the survey results from the Chinese literature; rather, we 241