Experimental reintroduction and host preference of the microendemic and endangered orchid Barkeria whartoniana in a Mexican Tropical Dry Forest

Barkeria whartoniana is an epiphytic, microendemic orchid of southern Mexico. This species exclusively inhabits limestone outcrops within a tropical dry forest in Oaxaca State, and its current population size is very small. The goals of this study were to characterize its phorophyte preference, and to assess the success of the experimental reintroduction of young individuals into its habitat. In an area of 15 km2 we censused all individuals of this orchid and estimated its area of occupancy. The occurrence frequency on different phorophytes was compared with the estimated densities of potential phorophytes. In July 2014, 76 orchid plants obtained through in vitro cultivation were reintroduced by attaching them on the trunks of two phorophyte species, one with rugose bark (Comocladia engleriana) and the other with smooth bark (Plumeria rubra). In the estimated area of occupancy of this orchid (0.016 km2), we only recorded 254 individuals, 42.4% of which were located on C. engleriana, suggesting a strong preference for this phorophyte. In October 2016, 13 reintroduced plants (ca. 17%) were still alive, almost all of which had successfully established. Initial plant size (stem length) emerged as an important driver of future survival. The artificial reintroduction of orchids facing extinction risk into their habitats may represent an efficient way to skip two critical phases in their life cycles, namely seed dispersal and establishment.