Elevational Gradients Drive Divergent Community Assembly Processes of Different Plant Community Types on the Highest Island of Fujian, China

Community assembly along elevational gradients may differ among plant community types, especially on islands where environmental stress and isolation are strong. We surveyed grassland, shrubland, and forest communities in low (<300 m) and high (>300 m) elevation zones on Dayu Shan Island, Fujian Province, China, and measured leaf functional traits of the dominant herb Miscanthus sinensis Andersson and shrub Mallotus japonicus (L.f.) Müll.Arg. We evaluated how elevation drives community assembly of the three community types, using β-diversity, phylogenetic structure, and intraspecific trait variation. In shrubland communities, total β-diversity and species turnover were higher in the low-elevation zone, and geographic distance was their strongest predictor, followed by elevation. In forest communities, elevation was the only significant predictor of β-diversity and species turnover. In grassland communities, the models explained little variation and were not significant overall, although elevation was the only significant individual predictor. The abundance-difference component did not differ between elevation zones in grassland or shrubland communities. Phylogenetic structure differed among community types. Forest communities showed a significant shift from random phylogenetic structure at low elevation to phylogenetic clustering at high elevation, with soil pH as the main correlate. Shrubland communities showed a marginal shift from phylogenetic clustering at low elevation to phylogenetic overdispersion at high elevation; their net relatedness index increased with aspect (southness) and decreased with wind speed. Grassland communities did not differ significantly between elevation zones and remained predominantly phylogenetically random, with soil pH as the main environmental correlate. At high elevation zones, M. sinensis had thinner leaves and higher leaf nitrogen content, while M. japonicus had lower specific leaf area and higher leaf tissue density. Overall, different community types responded divergently to elevational change, highlighting the need for functional-group-specific conservation.