Rare species contribute greater to ecosystem multifunctionality in a subtropical forest than common species due to their functional diversity

Global environmental change and increased human activities have led to rare species being given vulnerable status, as well as species losses and extinctions in recent years. However, most of the species in the community are rare species and they usually harbor unique functional traits that disproportionately contribute to community functional diversity. Numerous studies have also shown that functional diversity is a better predictor of ecosystem functioning than species diversity. Consequently, the evaluation of functional diversity of rare species and their contribution to ecosystem function is essential for the conservation of rare species. In this study, differences in functional diversity between rare and common plant species were analyzed based on functional diversity indices and species richness metrics in 30 1-ha plots comprising monsoonal evergreen broad-leaved forest in Pu’er City in the Yunnan Province of China. The roles of functional diversity of rare and common species in affecting ecosystem functions were also evaluated, in addition to the extent that either species group contributes to ecosystem functions or multifunctionality. The results indicated that functional diversity metrics including functional evenness and functional richness of rare species were higher than for common species in this subtropical forest. In addition, the functional diversity indices of rare species contributed greater to most ecosystem functions compared to those of common species. Moreover, the functional divergence of both rare and common species exerted obvious effects on ecosystem multifunctionality, although rare species exerted greater overall contributions. Rare species in the forest community of this study exhibited higher functional diversity and played a more important role in ecosystem multifunctionality via their diverse functional traits. Based on these results, it is necessary to focus greater conservation efforts on rare plants in a community.