Trait-Based Community Assembly in Early Tropical Forest Succession

Abstract

Aims: Widespread land-use change has expanded the area of young secondary forests. Yet, little is known about the drivers and mechanisms underlying their successional pathways, limiting the predictability of succession and its applicability in ecosystem restoration. We therefore assessed how dispersal, management, and environmental filters shape community assembly during tropical forest succession on abandoned agricultural fields. Location: Ghana. Methods: We established 18 permanent plots on abandoned subsistence fields in Ghana and monitored them over 4 years, yielding 67 plot–census combinations. The seed dispersal filter was quantified using surrounding landscape forest cover as a proxy, and the management filter was quantified on the basis of farmer interviews about land-use history. For environmental filters, soil nutrients were measured at the start, and understory irradiance and soil moisture were recorded during the first 2 years. To assess how these filters affected community assembly, we measured six functional traits for 122 species across seven growth forms and applied a fourth-corner analysis. Results: Forest structural development proceeded rapidly, particularly on fertile soils. Community assembly was jointly shaped by surrounding forest cover, land-use history, and environmental conditions. Greater quantity and quality (age) of the surrounding forests facilitated the establishment of species with resource-conservative trait values (e.g., high leaf dry matter content). Longer and more extensive previous land-use practices favored short-statured species with low leaf nitrogen concentration. Understory light availability declined with forest structural development, leading to a shift in the community from fast-growing annual herbs to evergreen woody species with resource-conservative trait values. Conclusion: Dispersal, management, and environmental filters collectively shaped community assembly, each playing distinct roles. Environmental filters strongly drove successional growth-form replacement; dispersal filters modestly influenced the rate of community reassembly, and management filters weakly shaped the initial species composition. Together, these filters shape early tropical forest succession and generate spatial variation in long-term successional trajectories.