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

We analysed the heterogeneity of high‐elevation vegetation on three mountains along a west‐east transect at 41 °S lat. in the Andes of northwestern Patagonia, Argentina. In this area, high‐Andean vegetation occurs as islands on mountain tops above Nothofagus pumilio forests ? with the timberline at ca. 1700 m a.s.l. We recorded floristic, topographic and substrate data in 166 sites stratified according to longitude, altitude, slope and aspect. Vegetation data were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis. The relationship between environmental and floristic variation was analysed using Canonical Correspondence Analysis. In order of importance, geographical longitude, altitude and aspect were the major determinants of vegetation variation, whereas substrate texture and slope appeared less important. The combination of these factors resulted in two main vegetation gradients. The first gradient is related to a moisture availability gradient, primarily determined by longitude and secondarily to variation in wind exposure (east vs. west aspect). The second vegetation gradient is related to variation in temperature, primarily determined by altitude, and secondarily by variation in insolation related to the contrast between north and south aspects. The four communities obtained with TWINSPAN are therefore associated with four characteristic habitat types: moist‐cold, moist‐warm, dry‐cold and dry‐warm. The community of warm and dry environments is the richest and has elements in common with dry steppe communities situated at lower elevations to the east, while the vegetation of the cold‐moist habitat type has unique elements that are typical of the southern Andes. Although current climatic factors appear to be the major determinants of high‐Andean vegetation gradients, historical events of Pleistocene times probably also affected the vegetation patterns we see today.