Maximising trait evenness promotes the recovery of plant species richness in managed grasslands

Land-use intensification threatens biodiversity, and restoring degraded ecosystems remains challenging because it requires identifying the rules that govern community assembly and dynamics. Investigating the temporal dynamics of trait-abundance distributions (TADs) offers a promising approach to disentangle the influence of stochastic (e.g., climatic variability, ecological drift) and deterministic processes (e.g., biotic interactions, abiotic filtering) on community dynamics and to guide biodiversity restoration in degraded systems.We used a long-term experiment (2004–2021) conducted in a species-poor, historically intensively managed grassland (Massif Central, France) to evaluate the relationships between land-use intensity, TAD dynamics, and plant species richness. TADs were quantified annually based on four traits related to plant size and leaf carbon economy. We analysed TADs temporal variability using the skewness–kurtosis relationship (SKR) framework, which accounts for the inherent stochasticity of ecological systems and helps reveal the imprint of deterministic processes on community assembly and dynamics.TADs dynamics was not random but constrained according to specific land-use and trait-dependent SKR patterns. Specifically, the cessation of fertilisation practices shifted TADs patterns from peaked, in the most intensively-managed treatments (i.e. the mown NPK-fertilised treatment), to even distributions in the mown and unfertilised treatment. In this treatment, TADs were more stable than expected by chance and closer to the skew-uniform distribution which define the maximum trait evenness. Change in TADs occurred in the early years of the experiment and preceded the recovery of grassland plant species richness observed in the unfertilised treatment.By accounting for the dynamic nature of ecological communities, our study provides new insights into how plant communities assemble and respond to land-use change. Our results suggest that maximising trait evenness for multiple traits can promotes the long-term recovery of a species richness in degraded grassland. In this context, the maximisation of trait evenness may serve as a valuable early indicator to guide management efforts and anticipate the success of ecological restoration. Our study opens research lines on the use of functional to develop a more predictive and actionable science in the face of global change in an era of global changes.