The role of environmental drivers in tree community structure of Central African lowland forests

Abstract

Tree communities vary at different spatial scales and are influenced by environmental factors. To understand the role of environmental factors in tree communities requires a scale-wise analysis. The overall objective of this study was to analyse the influence of environmental drivers (soil and climate) on three aspects of forest community structure (floristic patterns, tree height–diameter relationship and leaf functional traits) at regional (>100 km2) and local (0.5 km2) spatial scales.This study was conducted in Cameroon, Gabon and the Democratic Republic of the Congo, all belonging to the lowland (< 800 m) forests of Central Africa. At the regional scale, 133 non-contiguous permanent plots of one ha separated by at least 500 m were established in mature forests. Data from the 50 ha forest block were obtained for the local scale analysis. The later was split into 50 single one ha plots and each plot was subdivided into 25 quadrats of 20 m x 20 m. Ten soil and ten climatic variables were collected and analysed from 78 plots; five leaf functional traits (leaf area, specific leaf area, leaf phosphorus nitrogen content and nitrogen: phosphorus ratio) were measured only in Korup. Principal component analyses permitted to determine soil and climate gradients, and correspondence analysis with instrumental variables enabled to decompose their influence on floristic patterns. The Second-order polynomial model permitted to model tree height-diameter relationship while linear regression and correlation were employed for trait-gradient analysis with the help of R statistical software.At the regional scale in the moist forests of eastern Cameroon, floristic patterns were characterised by few “abundant species” (> one individual ha-1 per site) and by many “scarce species” (≤ one individual ha-1 per site). The gradients in soil composition (soil texture, phosphorus and organic fertility) explained 15.42 % (76/493) mostly scarce tree