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Over much of the world, conservation of regional biota depends almost entirely on the retention and management of the remnants of native vegetation left following clearing or extensive modification for agriculture, forestry, or other productive use. These remnants vary in size, shape, degree of isolation, and ownership. The fragmentation process results in many changes in the physical environment and in the biota, as reviewed by Saunders et al. (1991). In some parts of the world, as in Europe, fragmentation has been occurring for long periods (Wilcove et al. 1986; Attenborough 1987), whereas in areas more recently settled by Europeans, such as North America and Australia, the process has occurred mainly in the last 200 years (Hobbs and Hopkins 1990). Land clearance in many parts of the world, including Australia and the tropics, has been very rapid over the past 50 years (Saunders et al. 1985; Malingreau and Tucker 1988; Richards and Tucker 1988), and pressures from human population expansion are likely to see the fragmentation process continue (Western 1989). |
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