Disturbance regimes drive the diversity of regional floristic pools across Guianan rainforest landscapes

International audience

Английский. Disturbances control rainforest dynamics, and, according to the intermediate disturbance hypothesis (IDH), disturbance regime is a key driver of local diversity. Variations in disturbance regimes and their consequences on regional diversity at broad spatiotemporal scales are still poorly understood. Using multidisciplinary large-scale inventories and LiDAR acquisitions, we developed a robust indicator of disturbance regimes based on the frequency of a few early successional and widely distributed pioneer species. We demonstrate at the landscape scale that tree-species diversity and disturbance regimes vary with climate and relief. Significant relationships between the disturbance indicator, tree-species diversity and soil phosphorus content agree with the hypothesis that rainforest diversity is controlled both by disturbance regimes and long-term ecosystem stability. These effects explain the broad-scale patterns of floristic diversity observed between landscapes. In fact, species-rich forests in highlands, which have benefited from long-term stability combined with a moderate and regular regime of local disturbances, contrast with less diversified forests on recently shaped lowlands, which have undergone more recent changes and irregular dynamics. These results suggest that taking the current disturbance regime into account and including geomorphological stratifications in climate-vegetation models may be an effective way to improve the prediction of changes in species diversity under climate change. The Intermediate Disturbance Hypothesis (IDH) that predicts a humped diversity-disturbance relationship is at the same time inspiring for conservation policies 1,2 and subject to scientific controversy 3,4. The theory suggests that in highly diverse ecosystems, like the tropical rainforest, where competitive exclusion prevails in late successional processes 5 , an intermediate disturbance regime, i.e. of moderate intensity and/or frequency, locally reduces inter-individual competition for resources and thus allows less competitive species to avoid exclusion and to maintain in the community 6. There are empirical supports for IDH to locally maintain tropical rainforest in a non-equilibrium dynamics enhancing species diversity through gap-phase regeneration processes and secondary successions (e.g. refs 7-10). However, at larger scales corresponding to the extent of forest management options the diversity-disturbance relationship is actually not so clear. Spatio-temporal variations in resource availability, niche diversity or immigration fluxes (related e.g. to mass effects) may blur the expected diversity patterns that are observed at local scale (e.g. refs 11,12). For instance, Stropp and colleagues 13 inferred from wood density data across a network of 1-ha forest plots in Amazonia, that the frequency of disturbances was the main process driving local diversity, but not regional diversity, which they found more correlated to proxies of paleoclimatic stability and long-term ecosystem dynamics. These findings suggest that both local-and large-scale spatio-temporal dynamic processes interact in shaping the current pattern of