Dams have played an important role in human development throughout the world for thousands of years, providing water, controlling floods, irrigating crops, facilitating navigation, creating recreational opportunities, and generating motive power and elec- tricity. By the end of the 20th century, about 45000 large dams (15 m in height) and an estimated 800000 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 22000 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 terres- trial 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 worlds 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 envi- ronmental conditions of the region? A thorough assess- ment 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 informa- tion 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, we241 The Ecological Society of Americawww.frontiersinecology.orgREVIEWS REVIEWSREVIEWS The Three Gorges Dam: an ecological perspectiveJianguo Wu1,2, Jianhui Huang2, Xingguo Han2, Xianming Gao2, Fangliang He3, Mingxi Jiang4, Zhigang Jiang5, Richard B Primack6, and Zehao Shen7The Three Gorges Dam in China is the largest dam ever built. Its impacts on the biodiversity and ecologi- cal processes in the region are causing concern to ecologists worldwide. The dam and associated environ- mental alterations may result in a number of regional changes in terrestrial and aquatic biodiversity, as well as in ecosystem structure and functioning. The dam may also provide a rare opportunity for a grand- scale experiment in habitat fragmentation, allowing ecologists to develop and test a series of hypotheses concerning the dynamics of biodiversity and biotic communities and their responses to disturbances. Such research can help improve conservation practices, stimulate international collaborations, and promote public education on the environment. Front Ecol Environ 2004; 2(5): 2412481School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501 (Jingle.Wuasu.edu); 2Institute of Botany, Chinese Academy of Sciences, Beijing 100093, PR China; 3Department of Renewable Resources, University of Alberta, Edmonton, AB Canada T6G 2H1; 4Wuhan Institute of Botany, Chinese Academy of Sciences, Wuhan430074, PR China; 5Institute of Zoology, Chinese Academy ofSciences, Beijing 100080, PR China; 6Department of Biology, Boston University, Boston, MA 02215; 7Department of Ecology, PekingUniversity, Beijing 100871, PR ChinaIn a nutshell: The Three Gorges Dam (TGD) is the largest dam in the world The total area which will be influenced by the TGD is approx- imately 58 000 km2; about 1.13 million people will be displaced The Three Gorges Reservoir Region is an area of high bio- diversity, including a number of rare and endemic species TGD will inundate large areas of agricultural, forest, and grassland ecosystems TGD may serve as a grand-scale experiment in habitat frag- mentationThree Gorges Dam J Wu et al.will synthesize some major findings in the literature, discuss the possible ecological effects of the TGD, and then make suggestions for future research in this region.?Environmental setting of the Three Gorges Reservoir RegionThe Three Gorges Dam is built on the Yangtze River (Changjiang) in sout