Ferns as potential ecological indicators of edge effects in two types of Mexican forests

The edge effect impacts the richness, composition, and abundance of plant species, as a result of environmental changes caused by forest fragmentation. Ferns are considered important indicators of environmental quality because they are directly affected by these alterations. The purpose of this study was to analyze the influence of the edge effect on ferns of two tropical lowland rainforests and two montane forests in Mexico. We sampled twelve 10 × 10 m plots at the edge and forest interior of each site, summing up 96 sampling units. In each plot, fern species were inventoried, and vegetative, microclimatic and edaphic parameters were collected. We registered a total of 51 terrestrial fern species, distributed in 33 genera and 17 families. The edge effect was considerably stronger at the montane forest sites, which had the highest fern richness and abundance in the forest interior, but experienced strong alterations of the fern species composition at the forest edge. This reduction of species richness and abundance was accompanied by significant changes in the environment at the montane forest sites, where canopy openness, temperatures, and wind speed increased, and soil moisture and air humidity significantly decreased. However, at the lowland rainforest sites the edge effect only weakly affected the abiotic environment and fern species composition. Half of the fern species were good indicators of forest interior or forest edge. We conclude that edge effects on ferns are more pronounced in montane forests than in lowland rainforests. Thus, conservation efforts to protect ferns should prioritize on threatened montane forests that are the hotspots of fern diversity, yet without ignoring lowland rainforests that contain a less diverse but distinct fern flora. Because many ferns were good indicators of the forest alterations caused by edge effects, we suggest using them as tools to evaluate the success of restoration efforts on habitat quality along forest edges.