Shifts in the Relationship Between Plant Species Diversity and Functional Diversity During Ecosystem Degradation Succession

ABSTRACT Plant diversity, including species and functional diversity, plays key roles in driving ecosystem material cycling and energy flow, and maintains ecosystem stability and service functions through dynamic interactions during succession. However, their relationship remains poorly understood in the context of ecosystem degradation succession. In a representative karst rocky desertification (KRD) area in southwestern China, we investigated plant species diversity and functional diversity across KRD succession using a space‐for‐time substitution approach, aiming to examine how plant species diversity relates to functional diversity and how both change during ecosystem succession. 127 plant taxa belonging to 47 families and 96 genera were recorded in the KRD vegetation survey. Results showed that KRD ecosystems generally exhibited low plant species diversity. The mean values of the Margalef, Shannon‐Wiener, Simpson and Pielou indices were not more than 2.5, 2.0, 0.85, and 0.9, respectively. Shannon‐Wiener, Simpson, and Pielou indices varied considerably across different KRD stages. The mean values of plant functional diversity indices (richness, evenness, divergence, disperence, and Rao's quadratic entropy) were no more than 18, 1.7, 1.6, 12, and 11, respectively. As KRD succession, these five plant functional diversity indices all underwent significant changes. Significant correlations between plant species and functional diversity were consistently observed across all KRD stages, and the underlying driving mechanisms of their coupling relationship were revealed. The synergistic evolution of plant functional traits and soil factors during KRD succession was quantified. This study revealed a dynamic shift from synergy to trade‐off between plant species diversity and functional diversity in the KRD process. These findings are of great significance for understanding the evolutionary mechanisms of biodiversity during terrestrial ecosystem succession and providing applicable strategies for KRD vegetation restoration.