Abstract:

Aims: Semi-humid evergreen broad-leaved forest (SEBF) represents a distinct sub-type of evergreen broad-leaved forests within the subtropical region of western China. Despite their ecological significance, the functional diversity of SEBFs remains in adequately understood. This study aims to conduct a comprehensive analysis of plant traits and functional diversity within SEBFs and elucidate the environmental factors influencing their variations.

Methods: This research was conducted across the expanse of the Central Yunnan Plateau, the primary natural habitat for SEBFs. We conducted surveys within five well-protected SEBF sites, namely Jinguangsi (JGS), Jizu Mountains (JZS), Diaoling Mountains (DLS), Qiongzhusi (QZS), and Zhujiangyuan (ZJY). A total of 29 plots measuring 20 m × 20 m were sampled. Key plant traits including the maximum height (H_max), specific leaf area (SLA), and wood density, were recorded for collected samples. Functional diversity indices such as functional richness (FRic), functional divergence (FDiv), functional evenness (FEve), and functional redundancy (Rstar) were calculated based on these traits. Additionally, life-form spectrums and community-weighted mean trait values (CWM) were assessed for different sample sites and community types. Environmental factor analysis, using variance partitioning, was employed to gauge the impact of various ecological factors on the variations in functional diversity within SEBFs.

Results: Within the semi-humid evergreen broad-leaved forests (SEBFs) of the Central Yunnan Plateau, the CWM of key traits, namely H_max, SLA and wood density, exhibited no significant differences among various sample sites and community types. The shrub layer demonstrated higher CWM_SLA values compared to the tree layer, while their CWM_wood_density remained consistent at 0.5 g/cm³. In terms of diversity, both species diversity and functional diversity varied between the tree layer and shrub layer. Notably, JZS and DLS exhibited the highest values for FRic, FEve, and Rstar, indicating greater resilience and stability in these two sample sites. However, different community types of SEBFs, based on various dominant species, displayed similar FDiv, FEve, and Rstar values, differing only in FRic. FRic and Rstar were both significantly positively correlated with species richness (P < 0.05), while their relationships with other functional diversity indices were not significant. Factor analysis revealed that climate and soil nutrient contributed more than 60% of variances in CWM and functional diversity within SBEFs. Additionally, human activities emerged as influential factors in shaping the functional diversity of these forest communities.

Conclusion: Our results shed light on the characteristics of CWM values and functional diversity within the SEBFs, particularly in the context of tree layer and shrub layer. We have observed distinct spatial variations across different sample sites. Interestingly, despite the existence of different community types based on various dominant species, these communities occupy different functional niches yet exhibit a remarkable degree of functional convergence in terms of directional divergence, evenness, and redundancy. These findings provide valuable insights into the functional diversity of SEBFs, which, in turn, can inform and enhance efforts related to forest conservation and biodiversity restoration.

Key words: semi-humid evergreen broad-leaved forest, community-weighted mean trait values, community functional diversity, environmental determinants