Suchergebnisse

Understanding the processes that foster species coexistence is a longstanding goal in community ecology. Trade-offs in species performances for different ecological functions have been proposed as a general mechanism of species assemblage. The nature of these trade-offs can be revealed by analysing the demographic characteristics of species combined with their functional traits (FT) and the surrounding environment. The respective roles of soil, stand structure, and the functional dissimilarity of the neighbourhood, to the variations of growth, recruitment, and survival were determined for 19 most frequent tree species examined at the individual level in a tropical dry woodland (miombo; Democratic Republic of the Congo). Four functional groups can be recognised by contrasting life-history strategies and mainly related to tree stature, leaf phenology, leaf area (LA), leaf nutrient content, ectomycorrhizal status, and dispersal mode. Growth is regulated by the functional dissimilarity of the neighbourhood, local stand structure, and soil conditions. Recruitment is comparatively less impacted by functional neighbourhood but is mainly influenced by stand basal area and mean DBH as well as available calcium. At the community level, survival is mainly explained by physical and chemical soil variables and by both negative and positive effects of traits dissimilarity with the neighbourhood. Functional dissimilarity of the neighbourhood has the greatest positive effect on growth and survival, whereas competitive hierarchy is detrimental for growth of Caesalpinioideae species in particular, and for survival to a lesser extent. The general involvement of foliar traits and stand basal area on demographic performances indicates that competition for light is a key axis of species niche differentiation along the fast-slow continuum, even in this tropical dry woodland. Our results also pointed out a trade-off between water resources and phosphorus availability or aluminium avoidance, which separates growth strategies and leads ...

Aims: Relationships between local habitat heterogeneity and tree communities in miombo woodlands have been very little studied. While some studies have addressed this topic at broad scales and based on few environmental parameters, this study aims at 1) detecting fine-scale habitats (≤ 10 ha) on the basis of a detailed characterisation of soil explicitly considering past anthropogenic disturbances, and an exhaustive census of the tree community, and at 2) searching for indicator tree species corresponding to the resulting habitats.Methods: The study was carried out in the miombo woodland of Mikembo Forest Reserve, Upper Katanga, The Democratic Republic of the Congo. A complete census of the tree community was conducted in a 10-ha forest dynamics plot comprising 160 adjacent quadrats of 25 × 25 m, with a total of 4604 trees (DBH > 10 cm). Thirty-six physicochemical soil parameters were measured. Studying the frequency distribution of soil charcoal content allowed identifying local signature of past human agriculture in the soil. Two strategies were used to define habitats: 1) a combination of PCA on soil variables and Ward clustering, and 2) Multivariate Regression Trees (MRT) to search for key soil parameters allowing the best prediction of species composition. Tree-habitat associations were tested by means of a robust statistical framework combining the IndVal index and torus randomisations.Important findings: The forest contained 82 tree species and a significant proportion of wet miombo species (e.g. Marquesia macroura). We detected a strong east-west edaphic gradient driven by soil texture; most chemical soil parameters followed this pattern. Five habitats were identified based on soil factors and floristic composition. Nine indicator species of these habitats were found. The key soil factors discriminating habitats were total calcium, available forms of phosphorus, and clay content. Even though past agricultural practices were successfully detected in soils, they did not display any significant influence ...