The use by rain forest mammals of natural forest fragments in an equatorial African savanna

Two contrasting vegetation types occur in the Lope Reserve in central Gabon: tropical rain forest dominates but areas of savanna containing natural forest fragments also exist. How forest mammals use the forest fragments has broad implications for conservation and management of tropical ecosystems because the natural landscape at Lope mimics the fragmentation of forests produced increasingly by human action. The Lope savannas result from climate induced vegetation changes over the past 20,000 years and are currently maintained by active management because, without regular burning, they are colonized by forest. Forty-five species of large mammal (body weight greater than or equal to 2 kg) have been recorded at Lope and, although none are savanna specialists, some use the savanna habitat. Sweep censuses were conducted monthly over 2 years in 13 forest fragments. The census sites were small (0.4-11 ha), completely or largely surrounded by savanna, and up to 450 m from continuous rain forest. Population density and biomass were calculated for the 26 species of mammals encountered (nocturnal species were rarely seen) and compared to data previously collected in adjacent continuous forests. Total biomass (6010 kg km(-2)) was highest in the forest fragments. Compared to adjacent, continuous forest, elephants (Loxodonta africana) were less common whereas buffalo (Syncerus caffer) and red river bog (Potamochoerus porcus) were much more numerous. Of eight species of diurnal primates, four were more common, two occurred at similar densities, and two were much less common in the fragmented habitat. Most mammalian species moved between continuous forest and the fragments but two species of guenon and six species of duiker appeared to reside permanently in some fragments. The diversity and high biomass of large mammals found within the forest outliers at Lope is surprising and suggests that fragmentation per se will not be catastrophic for most of these species.