Influence of habitat attributes on terrestrial orchid communities across a tropical forest recovery gradient

Understanding drivers of plant diversity and distributions is critical for their conservation, particularly among changing environments. While plants’ responses to disturbances are relatively well-studied, in-depth analyses of how they respond to habitat recovery are surprisingly scarce. This is particularly true for one of the most diverse, sensitive, and threatened plant families: the Orchidaceae. To address this knowledge gap, we evaluated the diversity and distribution of terrestrial orchid species within a recovering tropical forest landscape in the Republic of Palau. We tested the hypotheses that orchid abundance, richness, and diversity vary across a forest successional gradient and that orchid species exhibit specificity and/or fidelity to particular tree species. Surveys yielded distribution data for 23 orchid species and General Linear Models revealed that habitat type and tree abundance, diversity, and size significantly affected orchid abundance. Habitat type and tree abundance also affected orchid richness and diversity. Indicator analysis showed that only two orchid species were significantly associated with individual tree species. The local landscape-scale study established that orchid communities varied across habitats and that mature forests had greater orchid abundance, richness, and diversity. Interestingly, tree abundance had a stronger influence on orchid communities than tree diversity, tree size, or specific tree species. The study demonstrated that orchids can occupy a range of successional habitats and indicated that reservation strategies paired with restoration efforts utilizing various tree species for reforestation will benefit orchid communities over potentially shorter timeframes than might occur without active management.