Environmental heterogeneity and its influence on fern diversity: A case study in the low-altitude mountain forest in central Taiwan

Environmental heterogeneity plays a crucial role in shaping the distribution and composition of natural vegetation, including understory ferns. As ferns are highly sensitive to environmental fluctuations, they are often regarded as effective ecological indicators. This study investigates the influence of environmental variation on understory fern communities within a one-hectare permanent plot in a low-altitude mountainous forest in central Taiwan. A total of 51 fern species (including Lycophytes), belonging to 20 families and 30 genera, were recorded. Among these, 43 were terrestrial and eight epiphytic species; however, only terrestrial species were analyzed due to limited representation of epiphytes. Multiple regression analyses identified four to eight key environmental variables influencing fern richness, abundance, and composition, with topographic factors—particularly stream distance—being most frequently selected. Two-way indicator species analysis (TWINSPAN) categorized the ferns into four distinct groups, while Canonical Correspondence Analysis (CCA) revealed that elevation and stream distance significantly explained compositional variation among these groups. This study underscores the role of topographic and soil-related heterogeneity in structuring fern communities and highlights potential indicator species for future ecological monitoring in subtropical forest ecosystems.