Interactions between epiphytes during canopy soil formation: an experiment in a lower montane cloud forest of southeastern Mexico.

In several montane forests around the world, epiphytes coexist in mats, sharing the rhizosphere and forming histosol-type soils rich in nutrients. The role of these epiphytes in the formation of canopy soil and the fitness costs that epiphytes face when cohabiting in these mats are unknown. In a lower montane cloud forest in central Veracruz, Mexico, a two-year factorial experiment was carried out with the presence/absence of ramets of Phlebodium areolatum (Polypodiaceae), Tillandsia kirchhoffiana, T. multicaulis, and T. punctulata (Bromeliaceae). With this experiment: a) we tested which epiphyte species contribute to the formation of canopy soil, b) we explored the role of epiphyte composition in the soil nutrient composition, and c) we determined the fitness costs faced by epiphytes when cohabiting. Canopy soil formation occurs to a greater extent when P. areolatum is present. Soil nutrient content does not change with epiphyte composition, is influenced by the microbiota, and P decrease with the presence of epiphytes. The fitness costs show that the species compete, decreasing their survival and growth, but the competitive capacity is different between the species. We conclude that P. areolatum is an ecosystem engineer that promotes the creation of canopy soil but is a poor competitor; these facts coincide with the model of succession by facilitation. Canopy soil is a slow-created component whose nutrient content does not depend on the epiphytic flora. In epiphyte mats, the dominant interactions are competitive, but there is also facilitation.