Water table depth may influence the asymmetric arrangement of epiphytic bromeliads in a tropical dry forest

Abstract

Studies of metapopulations of epiphytic bromeliads have been useful to test dispersal limitations and niche effects on the distribution of species, but most studies have been done in wet forests. To advance understanding of these processes in dry environments and using additional microclimatic data, we examined the horizontal distribution, vertical stratification and abundance of epiphytic bromeliads in trees from a dry forest and tested whether water table depth (indicated by the distance to an exposed underground lake, cenote) influenced the microenvironment or structure of the vegetation. Seasonal microenvironmental variables (relative humidity, temperature and light) were characterized among sites, two tree species and three vertical canopy strata. Epiphytes and trees were surveyed in plots, and various tree traits were recorded. Epiphyte density decreased with distance from the cenote (water hole) as the water table became farther from the ground surface and thus unavailable to trees. Sites close to the cenote had higher nighttime humidity, irrespective of the tree species identity. Within the same tree species, the base of the canopy was lower at sites close to the cenote, denoting that the cenote influenced the structure of the canopy. These factors may determine the distribution of the epiphytes by positively influencing the water status of these nocturnally transpiring plants with Crassulacean acid metabolism. Epiphytes were distributed randomly among all the species of trees close to the cenote, but they exhibited a species-specific vertical stratification, which may reflect physiological differences among the epiphyte species.