Wild epiphytic orchid diversity and phorophyte preference along micro-environmental gradients in north-eastern protected forest areas of Bangladesh

Understanding epiphytic orchid diversity and their ecological associations with phorophytes is critical for effective forest conservation. This study assessed species richness, diversity, and orchid-phorophyte interactions along eight micro-environmental habitat variables (phorophyte height, BDH, bark thickness, phorophyte crown height, orchid attachment height, nearest forest edge distance, canopy coverage & elevation) 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 within 12 genera were recorded, hosted by 74 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 identified the most abundant orchid species, including Cymbidium finalaysonianum in RKWS and Dendrobium lindleyi in LNP. phorophyte specificity analysis revealed Aerides and Cymbidium as generalists occurring on 26 phorophyte species, while Camarotis and Phalaenopsis were specialists, found on only 3 phorophyte species. Artocarpus emerged as the most supportive host, associating with 11 orchid species. Micro-environmental factors such as phorophyte 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 phorophyte diameter, influenced orchid distribution patterns. These findings depicted that both phorophyte diversity and habitat microclimatic conditions play vital roles in the colonization and sustainability of wild epiphytic orchid populations. Conservation strategies should prioritize maintaining phorophyte diversity and favorable microhabitat conditions to ensure the persistence of these epiphytic orchid species under environmental change scenario.