Three Gorges project: chance and challenge.

THE THREE GORGES DAM (TGD) ACROSS THE Yangtze River is the world’s largest hydroelectric dam (1). Construction of the TGD will form many different sizes of islands, providing a golden opportunity for exploring the ways in which island ecosystems are regulated (1). However, the construction will also pose great challenges to the ecosystem of the Three Gorges Reservoir Area (TGRA). It will affect the livelihood of at least 20 million people above the dam and another 300 million downstream (2), and it will fragment large, continuous habitats into smaller patches through dam-related activities such as construction of new cities, counties, townships, and roads (see figure). These activities will alter the diversity and composition of biota (3, 4), change ecological processes like nutrient and water cycling (5), and ultimately pose a great threat to the ecological safety of both the TGRA and the vast regions of middle and lower reaches of the Yangtze River (6). Furthermore, information on the expected impacts of ecosystem fragmentation in the TGRA is lacking; it is thus urgent to carry out empirical studies about this fragmentation. The following measures are proposed for the TGRA, but may also have important implications for many other parts of the world. 1) On-the-spot monitoring stations that evaluate the impact of ecosystem fragmentation are urgently needed. The TGRA will alter natural hierarchies of system organization, and little is known about this process. Although 22 on-the-spot stations have been established for research and monitoring purposes in the TGRA, only a few offer programs to study ecosystem fragmentation. 2) A landscape-based approach is required to plan, implement, and evaluate the phases of the TGD project development. This approach would take into account interactions and interdependencies of physical, chemical, and biological, as well as social and economic aspects of the TGRA. Adopting a landscape-based approach means identifying these interrelationships, predicting the impact of any proposed action, and evaluating the consequences before making any decisions (7). 3) It is crucial to set aside more areas of land in the TGRA as protected parks and natural reserves. These reserves will provide natural colonists for the regeneration of degraded ecosystems. It is also necessary to connect isolated patches with corridors to other areas in the TGRA to help increase the exchange of individuals between habitat patches, promote genetic exchange, and reduce population fluctuations (8). By the end of 2003, the natural reserves covered about 6.9% of the TGRA’s area, and the natural reserves in China covered about 15% of the national area during the same period (9). The ecosystem of TGRA is so diverse that one of the three richest flora centers in China is located in it (5). So the current natural reserve coverage is too small to ensure survival of some species and to sustain ecosystem functions. To protect its biodiversity, natural reserves should cover at least 15% of the TGRA’s area. Interdisciplinary research across national boundaries is needed to answer complex questions regarding habitat fragmentation in the TGRA. GUOZHEN SHEN AND ZONGQIANG XIE* Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, People’s Republic of China. *To whom correspondence should be addressed. Email: [email protected]