Changes in structure and composition of evergreen forests on an altitudinal gradient in the Venezuelan Guayana shield.

摘要: There have been several ecological studies in forests of the Guayana Shield, but so far none had examined changes structure and composition evergreen with altitude. This study describes analyzes structure, species soil characteristics forest stands at different altitudinal zones Southeastern Venezuelan Guayana, order to explain patterns main factors that determine along gradient. Inventories 3 948 big (>10cm DBH) 1 328 small (5-10cm woody stems were carried out eleven plots, ranging from 0.1 1.0ha, a 188km long transect elevations between 290 395masl. It has found 1) hemiepihytes become more dominant lianas reduce their dominance increasing altitude 2) area is size-dependent. Five families 12 genera represented only 9% total number genera, respectively, recorded troughout gradient, two groups taxa comprised than 50% Importance Value (the sum relative density dominance) all measured stems. Moreover, results suggest low richness seems be associated one or few species. Stand-level wood (WD) trees decreased significantly elevation. WD an indicator trees'life history strategy. Its decline suggests change functional The Canonical Correspondence Analysis (CCA) indicated distinction studied on basis levels geographic location, revealed responses by forests, environmental variables variation composition, terms basal among stands, was controlled primarily elevation secondarily rainfall conditions. are other interacting not considered this like disturbance regime, biological interactions, productivity, dispersal history, which could affect In conclusion, it appears structural floristic variability observed produced combination climates randomly expressed local processes across complex physical landscape. Rev. Biol. Trop. 60 (1): 11-33. Epub 2012 March 01.