Effects of Managed Disturbances on Plant Community Structure and Nutritional Function in the Tropical Savanna Habitat of the Endangered Eld’s Deer (Rucervus eldii)

Managed disturbances and their consequences for plant community structure, productivity, and foliar nutrients in the habitat of the endangered Eld’s deer remain inadequately characterized. We assessed the effects of prescribed fire (PF), mechanical mowing (MM), and their combination (PF_MM) on plant communities in the Datian National Nature Reserve of Hainan, China. Our findings demonstrated that the PF_MM treatment produced the greatest number of species (38 species, representing increases of 26.6% and 72.7% compared to PF and MM, respectively) and diversity indexes, indicating enhanced structural stability relevant to ecological conservation. In contrast, MM yielded the highest aboveground biomass (AGB) and the highest foliar nitrogen (N, 14.28 g kg−1), phosphorus (P, 2.08 g kg−1), and potassium (K, 3.61 g kg−1) concentrations, but concurrently promoted shrub dominance, potentially risking long-term nutrient depletion and functional group imbalance. Legume (Fabaceae) richness was negatively associated with foliar P and K, which is consistent with the nutrient dilution effect often observed in more diverse plant communities. Structural equation modeling indicated that treatment effects on AGB were mediated by the importance value of Fabaceae, whereas treatment effects on foliar N and P were expressed both directly and indirectly via the richness of Fabaceae and other families. Consequently, no single management approach can simultaneously enhance all desired metrics or indices. New management strategies or technologies should be explored to balance biodiversity conservation with improved pasture quality, thereby further supporting the recovery of Eld’s deer habitat while maintaining ecosystem health.