Implications of High Diversity for Forest Management
Present rates of species extinction throughout the world are at least several hundred times greater than the rate expected on the basis of the geological record (Dirzo and Raven 2003). The greatest losses are occurring in the tropics. Some of the losses result from invasion by exotic species. For example, the yellow crazy ant, Anoplolepis gracilipes, was introduced to Christmas Island in the Indian Ocean about 70 years ago. Populations exploded in the 1980s, forming super-colonies that infested one-fifth of the island. The ants eliminated the red land crab, a keystone consumer in the forest floor ecosystem (O'Dowd et al. 2003). Invasive plants also can cause extinction of endemic species through allelopathy, or the secretion of toxic chemical into the environment (Bais et al. 2003). However, habitat destruction is the most important driver of species extinction (Dirzo and Raven 2003).
Conservation of species is difficult to incorporate in forest management plans. It is not simple to design management strategies when many species have to be considered. For example, when deciding what trees to mark for se-
2.3 Reproductive Ecology of Tropical Trees
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