Comunidades vegetales y factores ambientales en los ca？adones costeros de Patagonia

the san jorge gulf district in patagonia has great interest for biodiversity conservation because it is subjected to intense mining and cattle raising. this paper describes the plant communities and their relation with environmental gradients in the coastal valleys of the eastern portion of the district. during three consecutive years, we measured plant composition and geographic, topographic, and soil environmental variables in 100 m2 plots. we identified eight plant communities grouped in three vegetation units: i) xerophytic scrub of nanofanerophytes, ii) xerophytic steppe of nanofanerophytes and hemicriptophytes, and iii) grassland of hydrophytes. these vegetation units were ordered across a gradient of soil and topography. two plant communities on coarsely textured soils (open and closed scrubs) were grouped at one end of the gradient, whereas one plant community on clay soils with high salinity (shrub steppes) was located at the other end. herbaceous steppes and herbaceous shrub steppes were located in an intermediate position of the gradient. the plant communities belonging to the xerophytic scrub of nanofanerophytes vegetation unit had the highest species richness and diversity. the soil (texture and salinity) and topographic gradients structured the vegetation units of these coastal valleys, as well as the distribution and diversity of plant communities.