Population structure and regeneration of multiple-use tree species in a semi-deciduous African tropical rainforest: Implications for primate conservation

The conservation of threatened frugivorous primates (e.g. chimpanzees) and birds in the Albertine Rift Ecoregion rainforests requires the conservation of food tree species aided by an understanding of their natural regeneration and population trends. However, little is known of the population structure and regeneration patterns of a wide range of multiple-use tree species in many of these forests. We examined the population structures and regeneration patterns of 15 tree species (including pioneer, non-pioneer and shade-bearers) that are both timber and primate food sources in Budongo Forest Reserve, NW Uganda, by constructing species population size-class distributions (SCDs), and calculating SCD slopes, seedling:juvenile and juvenile:adult ratios. The SCD slopes were used as indicators of population structure, while the slope values were used to summarise, in a single number, the shape of the SCD for a species. Species composition between forest communities varied significantly, suggesting the influence of spatial environmental variations. Nine species had significant positive correlations between seedling and adult densities. Nine species, namely Lasiodiscus mildbraedii, Celtis mildbraedii, Pouteria altissima, Chrysophyllum albidum, Cynometra alexandri, Diospyros abyssinica, Funtumia elastica, Chrysophyllum perpulchrum and Antiaris toxicaria had highly negative SCD slopes spanning -2.47 to -1.1, and juvenile:adult ratios spanning from 5.34 to 1.62. Hence, clearly exhibiting 'inverse J' type curves, and suggesting a successful or healthy regeneration pattern. In contrast, both Alstonia boonei and Cordia millenii had weakly negative SCD slopes of -0.25, and juvenile:adult ratios <1; hence a pulsed or discontinuous regeneration pattern and low recruitment. The SCD slopes and juvenile:adult ratios varied between forest communities and historical management practices (HMPs). Most species recruit successfully and continuously over time, and hence have a more stable population structure. However, a discontinuous regeneration pattern for some, reflects unsustainable harvesting, that potentially eliminates seed sources for future generations. Hence, management of the Budongo Forest Reserve requires plans/practices that will enhance and facilitate the recruitment of both the vigorously and poorly regenerating species to ensure sustainable forest development. Preserving some fruiting trees in logged areas will benefit both long-term sustainable timber production and wildlife conservation, by providing food for frugivorous animals that will disperse the seeds.