Spatio-temporal dynamics of Isoberlinia-dominated woodlands in disturbance-prone landscapes over 15 years

Abstract

Understanding the impact of productivity and disturbance on vegetation succession is a crucial debate in community ecology, with significant implications for biodiversity conservation. Productivity and disturbance influence species richness and structure, enhancing our understanding of vegetation dynamics and species coexistence over time. Numerous theories, such as the Intermediate Stress Hypothesis, Intermediate Disturbance Hypothesis, and Dynamic Equilibrium Model, have been proposed to explain these mechanisms. However, our understanding of how productivity and disturbance affect the spatio-temporal dynamics of Isoberlinia-dominated woodlands remains limited. We analyzed floristic data from sixteen sites with 64 permanent plots (400 m² each) along a south-north precipitation gradient (1112–991 mm per year) over 15 years (2006–2020). We calculated species richness and density for sapling and adult trees, and estimated two main variables: potential productivity using water deficit as a proxy, and disturbance intensity using logging rate. A linear mixed effects model, with plots nested within sites as random variables, was developed to test the effect of potential productivity and level of disturbance on species richness and density, for sapling and adult trees. Our results showed that species richness (SR) and density, for saplings and adult trees decreased over time, regardless of the disturbance and potential productivity gradients. Compared to higher levels of disturbance, low and medium levels of disturbance significantly increase the species richness of saplings and adult trees. In addition, the density of adult trees and saplings decreased over time, but increased with the level of disturbance from high to low. These results suggest that increased disturbance reduces the density of woodland species in favor of invasive species, typically savanna species. Overall, our results are consistent with the Dynamic Equilibrium Model, highlighting the complex interactions between disturbance regimes, productivity gradients, and their effects on species richness within ecosystems. Efficient forest management in Isoberlinia-dominated would avoid the high levels of logging that promote the establishment of invasive species and would maintain the biodiversity of this ecosystem in the long term.