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Background and aims - In low-precipitation environments, vascular epiphytes are expected to present low abundance and species richness, and could be restricted to inhabit a small number of phorophyte species. At the northern limit of the tropical region, in the southern Chihuahuan Desert, we determined epiphyte richness and biomass, and we tested whether Tillandsia recurvata exhibits phorophyte preference and whether vertical preference was exhibited within Prosopis laevigata.

Material and methods - In thirteen study sites covering the San Luis Potosi high plateau, southern area of the Chihuahuan Desert, Mexico, we established five parallel transects (10 x 50 m). In those transects, we sampled the epiphyte richness and we recorded the frequency of Tillandsia recurvata on its phorophyte species, and the abundance and the vertical distribution of T recurvata on Prosopis laevigata.

Key results - As expected, richness of holoepiphytes was weak (only one species: T recurvata). Frequency of T. recurvata between the phorophyte individuals was high (41% to 100% of the individuals) considering all phorophyte species. Dry biomass of T recurvata ranged from 0 to 9.4 kg per tree, and in the scrubland, ranged from 8.3 +/- 18.4 kg/ha to 491.9 +/- 92.3 kg/ha. Vertical distribution of the dry biomass of T recurvata on P. laevigata was similar between outer (15.1 +/- 15.7 gr/m of bark) and inner branches (12.2 +/- 13.6 gr/m of bark), but was lower on the trunk (0.8 +/- 1.4 g/m(2) of bark).

Conclusions - Our study shows that in our study area, one epiphyte species is present but it can invade all phorophyte species, most of the available phorophyte individuals and most of the vertical habitats. Even when precipitation limits the epiphyte richness, a single holoepiphyte species can reach biomass similar to that found in humid montane forest.