Post-agricultural forests are an increasingly extensive forest type globally, yet are often neglected by the ecological community and by conservation efforts, especially in the tropics, which have focused on forests perceived to be undisturbed by humans. Forests emerging on former agricultural landscapes can provide timber and fuel for humans, habitat for biodiversity, watershed protection and climate regulation. The unpredictability of successional patterns after diverse land uses makes it difficult to quantify these ecosystem services across the landscape. The legacy of prior land use is most often manifested in novel species assemblages, with implications for productivity and nutrient cycling processes. Here we explore hypotheses about relationships between species diversity and ecosystem function in the context of novel species assemblages emerging in post-agricultural tropical forests.
Drawing from our research in the Caribbean, we discuss patterns in above and belowground communities and associated ecosystem function in subtropical wet and seasonally dry post-agricultural forests on contrasting soil types. Tree species composition remained distinct even after almost a century. Soil microbial communities also showed strong successional patterns yet potential activity of extracellular enzymes involved in important carbon, nitrogen and phosphorus cycling did not differ with changes in community composition. Instead, enzymes showed a stronger seasonal trend in activity, reflecting soil moisture, and perhaps litter fall periodicity in some forests. Functional gene composition, another metric of microbial activity, did show differences between early and mid to late successional forests. On former sugarcane fields, the presence of an introduced N-fixing tree altered litter chemistry and decomposition rates. Forest structural components such as basal area and aboveground biomass accumulated quickly after the abandonment of land management and did not show strong patterns with increasing species richness. Understanding the legacies of past land use on ecosystem function will enhance our ability to manage and conserve tropical forests and improve our ability to predict their response to climate change and increased human pressures.