Revista Chilena de Historia Natural 77 (4): 649-660, 2004
RESEARCH ARTICLE
Distribution of grasses along an altitudinal gradient in a Venezuelan paramo
In Venezuelan paramos grasses, after Asteraceae, are the second family in numerical
importance. We studied their distribution in an altitudinal gradient located in Venezuela, Sierra de La Culata, between 2,500 and
4,200 m of altitude. Twenty one 32 m parallel line transects every 50 m were placed along the gradient, perpendicular to the main
slope. Each line was divided into contiguous 50 x 50 cm sampling units. Grass species occurrence inside each sample unit was
considered to determine their frequency in each line or altitude. The peak and altitudinal amplitude was determined through the
weighted averaging method. A total of 47 grass species were found along the gradient. Agrostis was the best-represented
genus in the gradient. Considering the distribution ranges, we assume that there are different biotic and abiotic processes determining
the distribution patterns. The species occurring at the highest altitudes were temperate elements, while those in the lowest areas were
tropical and subtropical elements. Seven species in the gradient are endemic to the Venezuelan paramos. Grass distribution patterns
in the paramo may be related to phytogeographical origin. In order to better understand the plant altitudinal distribution pattern is
necessary to consider the plant responses to low temperatures, high incoming radiation, water stress and slope aspect.
Key words:
altitudinal patterns,
phytogeography, Poaceae, South American Andes, tropical high mountain
