Pattern and driver of the compositional variations in a tropical cloud forest: Comparing vascular epiphytes with terrestrial woody plants

β-diversity patterns (the compositional variations across sites) and their
drivers are the major concerns of biodiversity research and conservation
practices, whereas such information remains scarce for vascular epiphytes,
especially in tropical forest communities. This study aimed to reveal the
pattern and driving process of the compositional variations of vascular
epiphytes in a tropical cloud forest on Hainan island, southern China, and
their differences from those of terrestrial woody plants. To this end, we
quantified their between-habitat compositional variations and
distinguished the underlying components of β-diversity (nestedness and
turnover). We then examined the relative roles of niche-based and neutral
processes in driving the compositional variations by using a null model
approach. Our results showed that the between-habitat compositional
variations were significant for both plant assemblages and stronger in
vascular epiphytes than in terrestrial woody plants. The turnover
component of β-diversity was significantly stronger in terrestrial woody
plants, accounting for 73.16%–80.08% of the variations. By contrast, the
nestedness component was significantly stronger in vascular epiphytes and
characterized 46.82%–67.5% of the variations. Besides, the compositional
variations of both plant assemblages, especially terrestrial woody plants,
were generally poorly fitted by the simulated niche-based scenarios but
well fitted by the simulated neutral scenarios. Overall, the compositional
variations of both plant assemblages were significant and mainly due to
dispersal limitation, albeit to varying degrees. Hence, further studies of
these plant assemblages at local scales should not be ideologically
limited to the niche-based framework. Moreover, the stronger nestedness
observed in vascular epiphytes suggests the greater importance of
prioritizing conservation efforts in the species-rich habitats for these
plants.