Host affinity and vertical distribution of epiphytic orchids in a montane cloud forest in southern Mexico

Abstract

Background: The host´s structural characteristics provide diverse microhabitats that influence the distribution patterns of the epiphytes at different vertical zones and among tree species.Hypotheses: Epiphytic orchids have preference for larger host trees and with non-exfoliating rough bark, while the limiting hosts will be those of smaller size and smooth and exfoliating bark, and there will be fewer individuals in the upper canopy of the host trees because the micro-environmental conditions are more stressful compared to the middle and lower parts of the host trees.Methods: The host preferences and vertical distribution of the epiphytic orchids were analyzed in 20 montane cloud forest fragments. In each fragment, two transects of 2 × 50 m were drawn, and the trees with a diameter at a breast height ? 20 cm were recorded. In each tree, basal area was quantified and bark texture was characterized. In each tree and vertical zone, the orchid species present were identified and quantified.Results: Orchid distribution patterns vary between vertical zones and host tree species, and the richness is related to host size and bark texture. The highest species richness and number of epiphytic orchid’s individuals were recorded in host trees with fissured bark and larger size. The distribution of orchids in the host was not homogeneous nor was it related to any particular host species. However, five trees species were considered as host preferred, while five tree species were limiting hosts. The highest richness was recorded in vertical zone II and the lowest in zones I and V.Conclusions: Larger trees contain greater richness of epiphytic orchids, because they offer better conditions for their establishment, provide a great diversity of microhabitats, greater time and area for epiphytic colonization events. The texture of the bark is a relevant factor in the host preference, and in the hosts with smooth bark, the presence of epiphytic orchids depends on the accumulation of organic matter.