Ravines as refuges for Orchidaceae in south-eastern Mexico

Abstract

Floristic studies of south-eastern Mexico have not considered the ravine component of the landscape and, in this study, we demonstrate the potential of ravines as refuges for orchids. At elevations of 1442–2358 m in the buffer zone of the Tacaná Volcano Biosphere Reserve, in the region of Soconusco, south-eastern Mexico, where 7.68% of the landscape has slopes > 45°, we registered 86 species of orchid from 35 genera, 14 (16.25%) of which were exclusive to ravines, 47 (54.6%) were exclusive to accessible surrounding areas and 25 (29%) colonized both types of habitat. The tropical mountain cloud forest (TMCF) ecosystem was distributed in the accessible areas surrounding the ravines and in some sites extended into the ravines themselves. Evergreen mountain scrub forest (EMSF), only found in the ravines, contributed eight species of orchid exclusive to this ecosystem. The elevation, orientation and slope of the ravines influenced species richness. The instability of the ‘soils’ on steep slopes and occasional landslides were negative environmental characteristics of the ravines, which, however, were mostly dependent on the management of surrounding areas, and epiphytes inhabiting ravines and the surrounding areas shared similar risks of whole-tree and branch fall, wind and torrential rain.