Comunidades vegetales y ambiente en el ecotono boreal entre los distritos patagónicos Central y Occidental (Río Negro, Argentina)

Abstract

With the objective of describing the vegetation of the northern extreme of the ecotone between the Central and Occidental Patagonian districts (Río Negro, Argentina), 58 floristic samples distributed in the main landscapes of the region were obtained. Their geographic coordinates, and topographic and edaphic parameters were registered. Precipitations were obtained by interpolation from 14 stations. Samples were classified using TWINSPAN method, and floristic composition of the different community types was compared with the vegetation representative of other regions, situated close to the study area. Main floristic gradients were obtained with Correspondence Analysis and vegetation-environment relations were detected with Canonical Correspondence Analysis. Six communities were delimited: 1) Grass-shrub steppe of Poa ligularis and Junellia mulinoides, 2) Grass-shrub steppe of Mulinum spinosum and Stipa speciosa, 3) Shrub-grass steppe of Stipa humilis and Nassauvia glomerulosa, 4) Shrub steppe of Nassauvia glomerulosa, Senecio filaginoides and Stipa humilis, 5) Shrub-grass steppe of Prosopis denudans, Atriplex lampa and Stipa humilis, 6) Shrub steppe of Atriplex lampa and Chuquiraga avellanedae. These communities were ordinated in a main gradient associated with altitude. The first two communities were exclusive of the basaltic plateaus, and represent the vegetation of the Occidental District described for other regions of Patagonia. Communities 3 and 4, at lower altitudes, represent a transition towards a more xerophilous phytogeographic unit, the Central District, and communities 5 and 6, in the lowest sites, are dominated by species characteristic of the Central District with Monte Phytogeographical Province elements. As altitude decreases, soils are deeper, more alkaline, and with finer textures.