Résumé
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 to habitat specialisation.
Multiple trade-offs allow species coexistence, with distinct drivers for tree growth, recruitment, and survival. Combining demographic and trait-based approaches provides unique key insights to understand species coexistence mechanisms.