Plant communities of a semi-deciduous tropical rainforest in north-western Uganda: role of soil and anthropogenic factors

Abstract

Forest plant communities were described using two floristic data sets (accompanied by data on soil and former management practices) from the Budongo Forest Reserve (BFR), Uganda – a semi-deciduous tropical rainforest. The first data set featured species basal-area data for woody species, while the other data set featured abundance for woody plants of stem diameter ≥ 2.0 cm. Four forest community types: Pseudospondias microcarpa Swamp Forest, Funtumia elastica–Pouteria altissima Forest, Lasiodiscus mildbraedii–Khaya anthotheca Forest, and Cynometra alexandri–Rinorea ilicifolia Forest were distinguished. Each community is characterised by a group of species, however there are a considerable number of species shared by all four communities. The forest communities show clear separation along gradients of screened soil characteristics (i.e. Organic matter, Na, N, Ca, Mg, and Si), corroborating the results suggested by the canonical correspondence analysis (CCA). For the species basal-area data, Axes 1 and 2 of the CCA explained 18 % in species, and 34 % of the variance in species-environment relations. Whereas, for the abundance data, the amount of information accounted for by the first two axes was 25 % and 44 %, in species variance and species-environment relations, respectively. Axis 1 of CCA was strongly correlated with soil nutrients, while Axis 2 was correlated with logging and arboricide treatment. Accordingly we interpret Axis 1 as an edaphic gradient, while Axis 2 is depicting an anthropogenic disturbance gradient.