Edge–Interior Differences in Plant Diversity and Herbaceous Functional Composition in Tropical Urban Remnant Forests: Associations with Invasive-Herb Dominance

Higher plant richness at forest edges does not by itself reveal whether native diversity is retained. We surveyed 196 plots in 28 tropical urban remnant forest patches in Haikou, China, comparing edge and interior vegetation. Herb richness and Shannon diversity were higher at edges, whereas adult-tree richness was lower. The total-herb-richness increase (1.94 species plot−1) was concentrated in invasive herbs (2.26 species plot−1); neither native-herb nor alien non-invasive-herb richness differed after FDR adjustment, whereas invasive-herb projected area increased. Edges also differed in projected-area-weighted functional composition, but richness-standardized functional diversity did not differ. Balanced Hill analyses corroborated higher local edge diversity at q = 0, 1, and 2, but this pattern did not translate into a parallel study-wide pooled gain in typical or dominant herb diversity. Edge communities were less dissimilar among patches under Bray–Curtis and Jaccard indices, and excluding widespread invasive herbs weakened these contrasts. Higher local herb diversity at forest edges therefore reflected changes in species origin, dominance, and among-patch composition rather than a uniform increase across species-origin groups, highlighting urban and peri-urban forest edges as priorities for invasive-herb surveillance and timely control.