How does species rarity influence the functional diversity and resilience along the successional pathway in heterogeneous karst forests?

Global climate change and human activities have increased the risk of rare species loss due to their sensitivity to disturbances. Considering their dominance in hyper-diverse communities, the contribution pathways and extent of rare species loss to functional diversity and resilience should be clarified. Therefore, we established 30 forest dynamic plots in heterogeneous degraded karst forests and measured the plant functional traits along the successional pathway. The correlations between trait uniqueness and species rarity were quantified, and the effects of rare and common species losses on functional diversity and trait networks were simulated. The correlations between trait uniqueness and species rarity showed that rare species tended to occupy marginal functional space positions in the mid- and late successional stages. In addition, rare species mainly supported functional redundancy in the early successional stage and significantly impacted functional resilience. In contrast, the unique traits supported by rare species increased along the successional pathway, thus increasing functional diversity and resilience in the late successional stage. This study highlights the crucial role of rare species in the functional diversity and resilience of degraded karst forests, warranting increased attention to rare species during biodiversity conservation and ecological management in heterogeneous, vulnerable ecosystems.