High Andean vegetation and environmental gradients in northwestern Patagonia, Argentina.

FERREYRA, M.,; CINGOLANI, A.,; EZCURRA, C.; BRAN, D.

JOURNAL OF VEGETATION SCIENCE

Intern. Assoc. Vegetation Science

Año: 1998 vol. 9 p. 307 - 316

1100-9233

We analysed the heterogeneity of high-elevationvegetation on three mountains along a west-east transect at41 O S lat. in the Andes of northwestern Patagonia, Argentina.In this area, high-Andean vegetation occurs as islands onmountain tops above Notlzofagus purnilio forests - with thetimberline at ca. 1700 m a.s.1. We recorded floristic, topographicand substrate data in 166 sites stratified according tolongitude, altitude, slope and aspect. Vegetation data wereclassified with TWINSPAN and ordinated with DetrendedCorrespondence Analysis. The relationship between environmentaland floristic variation was analysed using CanonicalCorrespondence Analysis. In order of importance, geographicallongitude, altitude and aspect were the major determinantsof vegetation variation, whereas substrate texture and slopeappeared less important. The combination of these factorsresulted in two main vegetation gradients. The first gradient isrelated to a moisture availability gradient, primarily determinedby longitude and secondarily to variation in windexposure (east vs. west aspect). The second vegetation gradientis related to variation in temperature, primarily determinedby altitude, and secondarily by variation in insolationrelated to the contrast between north and south aspects. Thefour communities obtained with TWINSPAN are thereforeassociated with four characteristic habitat types: moist-cold,moist-warm, dry-cold and dry-warm. The community of warmand dry environments is the richest and has elements in commonwith dry steppe communities situated at lower elevationsto the east, while the vegetation of the cold-moist habitat typehas unique elements that are typical of the southern Andes.Although current climatic factors appear to be the majordeterminants of high-Andean vegetation gradients, historicalevents of Pleistocene times probably also affected the vegetationpatterns we see today.Keywords: Alpine vegetation; Altitude; Andes; CorrespondenceAnalysis; Gradient analysis; Precipitation gradient; Temperaturegradient.