Diversity and endemism of tree ferns (Cyatheaceae: Polypodiopsida) in the Central Andes along latitudinal and elevation gradients

Abstract

Tree ferns are a conspicuous and yet poorly known component of Neotropical montane forests. Conservation efforts for these plants are hindered by a lack of information of patterns of species richness and endemism, which has been in turn prevented by an unstable taxonomy and limited collections. Based on distribution data from the most recent floristic accounts of tree ferns from Peru, Bolivia, and Argentina, this study presents an analysis of species richness and endemism of this group in the Central Andes. Results show that tree fern diversity falls steeply with distance from the equator, and the effect is stronger in the lowlands than at tree line to -20°. In elevation, tree fern species richness shows a bimodal distribution with peaks at 1000 and 2100 m, where as many as 24 species can coexist in 200 m elevation intervals. Endemic species are concentrated in the northern Central Andes. Endemics in more southern latitudes tend to be restricted to higher elevations. Correspondingly, the tree fern flora of the southern Central Andes is mostly composed of widely ranging species, potentially tolerant of higher seasonality and longer term climatic fluctuations. These results provide a tool for predicting how many tree fern species should be found in any given area of the Central Andes, even those botanically unexplored, and indicates areas where species richness and endemism is concentrated, and may serve to guide efforts aimed to conserve tropical montane forests.