STRUCTURE AND FUNCTION IN 2 TROPICAL GALLERY FOREST COMMUNITIES - IMPLICATIONS FOR FOREST CONSERVATION IN FRAGMENTED SYSTEMS

1. Composition, growth and turnover of trees in two species-rich tropi cal gallery forests were examined to evaluate what community reorganiz ation may be needed to transform recently created tropical forest frag ments into stable refugia for regional forest biotas. 2. Rates of tree growth and turnover over a 5-year interval were comparable to those r ecorded in continuous forests and in both communities there had been s ome tree species turnover in the measured stem size classes during the 5-year interval. 3. The more abundant tree species in both communitie s formed three functional groups along gradients between streams and f orest edges: edge-concentrators, core-concentrators and generalists. 4 . Soil fertility showed no consistent increase close to streams and ne ither tree growth nor recruitment rates were increased in this zone. I n contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests are light-limited rather than soil-limited, and that forest edge zones ar e generally favourable habitats for tree populations. 5. Both communit ies showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth-limited core habita ts is attributed to their fire sensitivity. 6. Rapid development of an edge zone of fire-insensitive tree species is considered to be essent ial to the survival of forest community fragments in the fire-prone la ndscapes of the tropics, and the edges of gallery forests are recommen ded as potential sources of species with which to fashion these protec tive ecotones. 7. Preservation of a diverse forest biota in the fire-p rotected interiors of fragments will require natural or artificially e nhanced immigration rates that are sufficient to offset local extincti ons.