Wild Epiphytic Orchid Diversity and Host Tree Preference along Micro-environmental Gradients in North-Eastern Forest Protected Areas of Bangladesh

Understanding epiphytic orchid diversity and their ecological associations with host trees is critical for effective forest conservation. This study assessed species richness, diversity, and orchid-host interactions along eight micro-environmental habitat variables across four protected forest areas in northeastern Bangladesh: Rema-Kalenga Wildlife Sanctuary (RKWS), Lawachara National Park (LNP), Satchari National Park (SNP), and Khadimnagar National Park (KNP). A total of 21 wild epiphytic orchid species under 12 genera were recorded, hosted by 68 tree species across 31 families. RKWS and LNP exhibited the highest species richness (20 species each), with RKWS also having the highest Shannon Diversity Index (2.84) and evenness (0.95), indicating a balanced and diverse orchid community. KNP demonstrated the lowest diversity (H' = 1.945) and species richness (9 sp.), indicating a fragmented ecosystem. Rank-abundance curves visualized dominant orchid species like Cymbidium finalaysonianum in RKWS and Dendrobium lindleyi in LNP. Host specificity analysis revealed Aerides and Cymbidium as generalists occurring on 26 host species, while Camarotis and Phalaenopsis were specialists, found on only 3 host species. Artocarpus emerged as the most supportive host, associating with 11 orchid species. Micro-environmental factors such as host tree height, crown height, bark thickness, and orchid attachment height showed significant positive correlations with orchid abundance. PCA and Mantel tests indicated that environmental gradients, particularly edge distance and altitude along with variables like- canopy coverage and host tree diameter, influenced orchid distribution patterns. These findings depicted that both host tree diversity and habitat microclimatic conditions play vital roles in colonizing sustaining wild epiphytic orchid populations. Conservation strategies should prioritize maintaining host diversity and favorable microhabitat conditions to ensure the persistence of these epiphytic orchid species under environmental change scenario.