MORPHOLOGICAL CHARACTERISTICS OF FERN ASSEMBLAGES ALONG AN ELEVATIONAL GRADIENT: PATTERNS AND CAUSES

Abstract

Based on species distribution data of 477 fern species along a tropical elevational gradient of 3300 m altitude, we analyzed the morphological patterns of species assemblages and related the patterns to environmental factors. Although close correlations of morphological traits and environmental drivers do not necessarily imply causality or function, a number of those morphological characteristics are also found in seed plants and have been tested widely regarding their relation to the ambient environment, and the results found within this study are in accordance with the main results for seed plants. High values of laminar thickness, combined with limited laminar dissection, are interpreted as defensive strategies against climatic extremes, especially at high elevations. High stomatal densities have also frequently been reported to occur at sites with low CO2 concentrations approaching high elevations. The main indument types, hairs and scales, although often assigned similar functions, may serve different functions, namely, respectively repelling and retaining water; comparable studies with seed plants have advocates for both hypotheses. Correlations between morphological traits and environmental drivers among plant groups of different lineage point to the increasing plausibility of such arguments. However, for pteridophytes, more studies of whole vegetation assemblages along extended environmental gradients are needed to verify the results found within this study. Accepted 15 March 2007.