Tropical forest succession and associated changes in community composition are driven by species’ demographic rates, but how demographic strategies shift during succession remains unclear. To identify generalities in demographic trade-offs and successional shifts in demographic strategies, we quantified demographic rates of 787 tree species from two wet and two dry Neotropical forests. Across all forests, we found two demographic trade-offs – the growth–survival and the stature–recruitment trade-off – enabling the data-driven assignment of species to five demographic strategies. Fast species dominated early in succession and were then replaced by long-lived pioneers in three forests. Intermediate and slow species increased in basal area over succession but in contrast to the current conceptual model, long-lived pioneers continued to dominate until the old-growth stage in all forests. The basal area of short-lived breeders was low across all successional stages. These results increase the mechanistic understanding and predictability of Neotropical forest succession.
Secondary tropical forests play an increasingly important role for carbon budgets and biodiversity conservation. Understanding successional trajectories is therefore imperative for guiding forest restoration and climate change mitigation efforts. Forest succession is driven by the demographic strategies (combinations of growth, mortality and recruitment rates) of the tree species in the community. However, our understanding of demographic diversity in tropical tree species stems almost exclusively from old-growth forests. Here, we assembled demographic information from repeated forest inventories along chronosequences in two wet (Costa Rica, Panama) and two dry (Mexico) Neotropical forests to assess whether the range of demographic strategies present in a community shifts across succession. We calculated demographic rates for >500 tree species while controlling for canopy status to compare demographic diversity in early successional (0-30 years), late successional (30-120 years) and old-growth forests. We quantified demographic diversity using two-dimensional hypervolumes of pairs of demographic rates and assessed whether shifts in demographic strategies were caused by intra-specific changes in demographic rates across succession or by species turnover. We expected that demographic strategies would shift from faster life-histories (fast growth, high mortality, high recruitment) in early successional forests to slower life histories (slow growth, low mortality, low recruitment) in old-growth forests and that shifts would be stronger in wet than in dry forests due to more pronounced differences in environmental conditions between early successional and old-growth forests. We also expected that demographic diversity would increase with succession. We found that demographic strategies largely overlapped across successional stages and that early successional stages already covered the full spectrum of demographic strategies found in old-growth forests. An exception was a group of species characterized by exceptionally high mortality rates that was confined to early successional stages in the two wet forests. Demographic diversity did not increase with succession. Our results suggest that current understanding of demographic strategies of tropical tree species, which has been generated mostly from long-term forest monitoring plots in old-growth forests, is largely representative of demographic diversity in general, and that demographic diversity recovers quickly during succession.
Aim Tropical forest succession and associated changes in community composition are driven by species demographic rates, but how demographic strategies shift during succession remains unclear. Our goal was to identify generalities in demographic trade‐offs and successional shifts in demographic strategies across Neotropical forests that cover a large rainfall gradient and to test whether the current conceptual model of tropical forest succession applies to wet and dry forests. Location Mexico and Central America. Time period 1985–2018. Major taxa studied Trees. Methods We used repeated forest inventory data from two wet and two dry forests to quantify demographic rates of 781 tree species. For each forest, we explored the main demographic trade‐offs and assigned tree species to five demographic groups by performing a weighted principal components analysis to account for differences in sample size. We aggregated the basal area and abundance across demographic groups to identify successional shifts in demographic strategies over the entire successional gradient from very young (<5 years) to old‐growth forests. Results Across all forests, we found two demographic trade‐offs, namely the growth–survival trade‐off and the stature–recruitment trade‐off, enabling the data‐driven assignment of species to five demographic strategies. Fast species dominated early in succession and were then replaced by long‐lived pioneers in three forests. Intermediate and slow species increased in basal area over succession in all forests, but, in contrast to the current conceptual model, long‐lived pioneers continued to dominate until the old‐growth stage in all forests. The basal area of short‐lived breeders was low across all successional stages. Main conclusions The current conceptual model of Neotropical forest succession should be revised to incorporate the dominance of long‐lived pioneers in late‐successional and old‐growth forests. Moreover, the definition of consistent demographic strategies that show clear dominance shifts across succession substantially improves the mechanistic understanding and predictability of Neotropical forest succession.
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