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. Quantifyin g this is an important step in prioritizing forest fragments for biodiversi ty conservation. Species-area curves from isolated forest fragments in Ghan a, West Africa, show that large forests contain the greatest number of tree species. Moreover, the additional species found within the larger forest f ragments follow a predictable pattern rather than acting as random compleme nts 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. T he use of species-area curves to determine the capacity of small forest rem nants to support species diversity should consequently be assessed with res pect to the component species. Increasing fragmentation will result in the loss of a valuable portion of the forest ecosystem: the ran and shade-toler ating species. These species will be more effectively preserved within larg er forest reserves. (C) 2001 Elsevier Science Ltd. All rights reserved.