Remnant large 'rescue' trees enhance epiphyte resilience to anthropogenic disturbance of pine-oak forests in the Highlands of Chiapas, Mexico

I studied vascular epiphytes in 16 pine-oak forest fragments within an 400 km2 relatively flat area at c. 2300 m elevation on an extended gradient of anthropogenic disturbance. Epiphyte biomass and species richness on 35 oak host trees in six diameter classes varied between the sites from 0.8 to 243 kg and from 13 to 34 species.
Forest disturbance, measured as the proportion of sprouted oaks, had an expected negative effect on the epiphyte biomass and alpha diversity per ground surface area, and also per 35 oak host trees (ANCOVA, P<0.001 with tree-size attributes as the covariates).
Stands which had previously been clear-cut were c. 25 years later structurally similar to old-growth forest, but still poor in epiphytes. Presumably, colonization from outside the forest fragment is a slow process. This is also suggested by the observation that epiphytes showed resilience to disturbance in fragments that were previously selectively logged to spare large trees, evidenced by the tree trunk diameter frequencies at present. Such remnant 'rescue' trees are essential for epiphytes that require the presence of accumulated suspended soil and may also serve as a nearby epiphyte seed source for the re-growing trees.
Anthropogenic disturbance also forces a shift from mesic- to more drought tolerant species. Hence, disturbance exerts an influence on the regional distribution of epiphytes. Environmental variables, including disturbance parameters, explained c. 25% of the variation between the sites, but a similar amount of variation could entirely be attributed to the geographic position of the sites in the landscape. Nearby fragments are more similar in epiphytes, using Raup & Crick's similarity coefficient, than distant sites (Mantel's r=0.44; P=0.002) and I postulate that this relates to the species composition of the seed rain, again viewing the development of the epiphyte community from a dispersal assembly perspective.
In the Highlands of Chiapas, pine-oak forests are an important source of timber and fuel for subsistence purposes. This vital function is not likely to change in the near future. To help preserve the diverse epiphyte vegetation it is recommend to abstain from periodically clear-cutting and in particularly to spare large 'rescue' trees when logging in order to boost epiphyte colonization. Also, is seems wise to address epiphyte conservation at large spatial scales such as per physiographic region.