Different major effects regulating productivity dynamics at different succession stages of monsoon evergreen broad-leaved forests

Introduction: Biodiversity has a significant impact on the formation and maintenance of ecosystem functions, and its role changes dynamically along with the ecological succession process. However, the relative contributions of biodiversity across different dimensions to ecosystem functions, as well as the patterns of change in these contributions during succession processes, remain unclear. Methods: This study selected four succession stages of monsoon evergreen broad-leaved forests (early succession, early-to-mid succession, mid-to-late succession, and late succession) as research subjects. Based on vegetation survey data, we calculated three biodiversity metrics (taxonomic diversity, functional diversity, phylogenetic diversity) and functional composition. Using forest productivity as an indicator of ecosystem function, we employed structural equation modeling to analyze how biodiversity across different dimensions at various succession stages influences productivity. This investigation explores how the relative contributions of selection effects, niche complementarity, and mass ratio effects to productivity change throughout forest succession. Results: The results indicate that: (1) As succession progresses, species richness, functional dispersion, and the phylogenetic PD index exhibit a unimodal pattern. Functional traits predominantly reflect resource acquisition in the early stages, shifting towards conservation in the later stages. Productivity shows fluctuating trends(P < 0.05); (2) The relationship between biodiversity and productivity changes with succession, showing an overall downward trend; (3) In the early succession stage, productivity is primarily driven by the mass ratio effect. During the middle to early succession stage, it is jointly driven by the selection effect and the niche complementarity effect. In the middle to late succession stage, it is mainly driven by the complementarity effect. There is no significant correlation between the late succession stage and biodiversity. Additionally, the local environment also has a significant impact on productivity. Discussion: The research findings are expected to provide scientific evidence for understanding the formation and maintenance patterns of monsoon evergreen broad-leaved forest ecosystem functions.