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.土地利用强度提升正威胁生物多样性，而退化生态系统的修复仍颇具挑战——这是因为我们需要先阐明调控群落构建与动态的内在规律。探究性状-多度分布（trait-abundance distributions, TADs）的时间动态，是厘清随机过程（如气候变异、生态漂变）与确定性过程（如生物间相互作用、非生物过滤）对群落动态的影响，并指导退化生态系统生物多样性修复的极具前景的途径。本研究依托2004年至2021年在法国中央高原（Massif Central）一处物种贫乏、历史上受高强度管理的草原开展的长期定位实验，探究土地利用强度、TADs动态与植物物种丰富度之间的关联。研究每年基于与植物体型及叶片碳经济策略相关的4个性状对TADs进行量化。本研究采用偏度-峰度关系（skewness–kurtosis relationship, SKR）框架分析TADs的时间变异特征，该框架可兼顾生态系统固有的随机性，有助于揭示确定性过程在群落构建与动态中的印记。研究结果显示，TADs的动态并非随机，而是受特定土地利用模式与性状依赖型SKR格局的约束。具体而言，施肥措施的终止使TADs格局发生转变：在最高强度管理的处理组（即刈割并施加氮磷钾复合肥的处理组）中，TADs呈尖峰分布；而在刈割且不施肥的处理组中，TADs呈均匀分布。在该处理组中，TADs的稳定性高于随机预期，且更接近定义了最大性状均匀度的偏态均匀分布。TADs的变化发生于实验早期，且早于不施肥处理组中观测到的草原植物物种丰富度恢复过程。本研究兼顾生态群落的动态本质，为解析植物群落的构建规律及其对土地利用变化的响应机制提供了新视角。研究结果表明，最大化多性状的性状均匀度，可促进退化草原的物种丰富度长期恢复。在此背景下，性状均匀度的最大化可作为一项极具价值的早期指标，用于指导修复管理实践并预判生态修复的成效。本研究开辟了新的研究路径：在全球变化时代，借助功能相关手段构建更具预测性与可操作性的科学体系，以应对全球环境变化。