Species composition in fragmented forests: conservation implications of changing forest area

An important aspect of forest fragmentation is the ensuing change in forest area and the impact this has on species number and composition. Quantifying this is an important step in prioritizing forest fragments for biodiversity conservation. Species-area curves from isolated forest fragments in Ghana, West Africa, show that large forests contain the greatest number of tree species. Moreover, the additional species found within the larger forest fragments follow a predictable pattern rather than acting as random complements from the community. The proportion of rare tree species increases with forest area, but common species form a stable foundation comprising around two-thirds of the total forest complement. As the area of forest fragments increases, edge effects decrease and the relative proportions of evergreen and shade-tolerating species increase with respect to deciduous pioneers. The use of species-area curves to determine the capacity of small forest remnants to support species diversity should consequently be assessed with respect to the component species. Increasing fragmentation will result in the loss of a valuable portion of the forest ecosystem: the ran and shade-tolerating species. These species will be more effectively preserved within larger forest reserves. (C) 2001 Elsevier Science Ltd. All rights reserved.