Resumen

BACH, Kerstin  y  GRADSTEIN, Stephan Robert. Vegetational hypsometric change of a cloud forest in Bolivian Yungas: Methods and altitudinal belts . Ecología en Bolivia [online]. 2007, vol.42, n.2, pp.83-101. ISSN 1605-2528.

Abstract We studied elevational limits of vegetation belts in the Yungas of Bolivia, in montane cloud forest between 1,700 and 3,400 m based on an assessment of species diversity of six vascular plant groups (aroids, bromeliads, cacti, ferns, melastoms, and palms). We analysed the similarity of 105 relevees of 400 m2, taken at eleva tional intervals of 50 m. We applied phytosociological analysis (Tabwin), multivariate ordination (DCA), cluster analysis (Ward), and parsimony analysis (PA UP*). Species turnover was determined by means of the Wilson-Shmida index and sta tistica 1 significance by means of a Monte Carlo simulation of species distributions. Phytosociological  analysis, cluster analysis, and parsimony analysis failed to resolve any significant elevational limits; while ordination revealed a major distance between groups of plots at 3,050 m. Significant borders at ca. 2,000 m (± 100 m) and at 3,050 m were based on a congruence of upper/ lower elevational limits of species ranges. Wilson-Shmida index values rarely approached 1.0 and none was significant. The study showed that sharply defined elevational belts for all groups of plants investigated could not be detected with the majority of the methods applied . The lack of borders presumably reflects the variation in species diversity patterns of the studied plant groups in relation to the gradual changes in abiotic factors along the gradient. Each group showed its own elevational pa tterns, presumably influenced by taxon-specific ecological traits. Also, the outcome of vegetation classification studies in species-rich tropical montane cloud forests seems to be strongly determined by applied methods and should be accurate with the study objectives.

Palabras clave : Tropical montane cloud forests; elevational belts; species turnover; G-diversity; Cotapata National Park.

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