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Keywords:

  • Altitudinal zonation;
  • bryophytes;
  • continuum concept;
  • cryptogams;
  • pteridophytes;
  • tropical mountains

Abstract

To test whether cryptogamic plant communities in tropical Andean rain forests are distributed in floristically discrete communities corresponding to altitudinal belts, I subjected the elevational distribution of pteridophytes along two elevational gradients in Bolivia, and of bryophytes and lichens along two transects in Peru and Colombia (data from Gradstein & Frahm, 1987; Wolf, 1993) to an analysis of deviance. All well-defined elevational boundaries in floristic composition were related to marked ecological changes: the transition from the steep mountains to the hilly lowland zone coupled with a change in geological substrate at 400 m along the Bolivian Carrasco transect, a strong humidity gradient at 1000 m at the Bolivian Masicurí transect and at 1250–1980 m along the Colombian transect, and the transition from mixed cloud forests to forests dominated by Polylepis or Podocarpus at 3400–3600 m in Carrasco, at 1650–1800 m in Masicurí, and at 3670 m in Colombia. Consequently, floristic elevational belts appear to be well-defined at strong environmental boundaries and in fairly species-poor forest communities where the presence or absence of one or a few tree species influences the whole ecosystem while they are ill-defined in species-rich communities such as tropical forests at low to mid-elevations.