Geomorphology, soil and vegetation patterns in an arid ecotone

Abstract

Ecotonal boundaries are often arranged by following topoedaphic gradients. Despite its relevance, the interrelationships between vegetation and geomorphology have not been adequately documented in most arid regions. The Southern Monte ? Patagonia ecotone, defined by anastomosing systems of paleochannels and paleobars, presents an opportunity to study these interrelationships. Our aim was to determine whether topography and/or soil characteristics explained the distribution of communities which are typical of both Phytogeographic Provinces. Vegetation and soil surveys were performed along topographical gradients found between several paleochannels and paleobars. Surface soil texture, organic carbon, total nitrogen, carbonate content and electric conductivity were measured at each site. Digital elevation models and moisture index maps were derived from topographical field data. Soil and plant cover differences between landforms were inspected. Afterwards, species distribution, communities´ attributes and its relation with topographical variables were explored. Paleochannels exhibited higher shrub and total cover, as well as higher organic carbon and lower carbonate content than the paleobars. Chuquiraga avellanedae (Asteraceae) dominated the plant community in the paleochannels, while on the contrary Larrea divaricata (Zygophyllaceae) was the most abundant species found on the paleobars. These communities are related to Patagonia and Monte Phytogeographic Provinces, respectively. Species distribution was mainly explained by elevation and secondly by surface water redistribution. Current vegetation patterns strongly mirror the paleolandscape and as a consequence of that, plant communities are interspersed throughout the landscape. Our results emphasize the importance of geomorphology as a factor influencing community distribution along arid ecotones.