Structure and function in two tropical gallery forest communities: implications for forest conservation in fragmented systems.
Abstract
Composition, growth and turnover of trees were examined in 2 species-rich tropical gallery forests in the Mountain Pine Ridge Savanna of Belize during 1996, to evaluate what community reorganization is needed to transform recently created tropical forest fragments into stable refugia for regional forest biotas. Rates of tree growth and turnover over a 5-year interval were comparable to those recorded in continuous forests and in both communities some tree species turnover was observed in the measured stem size classes. The more abundant tree species in both communities formed 3 functional groups along gradients between streams and forest edges (edge-concentrators, core-concentrators and generalists). Soil fertility did not increase close to streams and neither tree growth nor recruitment rates were increased in this zone. In contrast, forest edge zones exhibited increased rates of tree growth and recruitment indicating that growth processes in these forests were light-limited rather than soil-limited. Both communities showed signs of past fire incursions, and the tendency of a subset of tree species to concentrate in the more growth-limited core habitats was attributed to their fire sensitivity. It is concluded that rapid development of an edge zone of fire-insensitive tree species is essential to the survival of forest community fragments in the fire-prone landscapes of the tropics, and that the edges of gallery forests are recommended as potential sources of species with which to fashion these protective ecotones. It is suggested that the preservation of a diverse forest biota in the fire-protected interiors of forest fragments may require natural or artificially enhanced immigration rates that are sufficient to offset local extinctions.
Key words
- botanical composition
- canopy gaps
- fire ecology
- forest borders
- forest ecology
- forest fires
- forest fragmentation
- forest management
- forests
- fragmentation
- growth
- growth rate
- habitats
- immigration
- light
- light penetration
- natural regeneration
- nature conservation
- plant communities
- population dynamics
- riparian forests
- soil fertility
- species diversity
- streams
- synecology
- tropical forests
- tropics