Factores asociados a la invasión de pajas en bosques de la región semiárida central argentina

Abstract

(Palabras clave: pastoreo, recursos del suelo, palatabilidad, estrategias de uso de recursos) ABSTRACT. Factors associated to invasion by non-palatable grasses in Argentinean semi-arid forest: In semiarid Prosopis caldenia forests of the central region of Argentina, unpalatable native tussock grasses, Jarava ichu and Nassella tenuissima, have expanded their range and abundance, reducing plant diversity and forage productivity. This expansion may be related to domestic grazing. It becomes relevant, therefore, to evaluate the relationship between the intensity of grazing, the abundance of the tussock grasses, and its possible effects on soil factors. We made vegetation censuses and soil sample analyses in different grazing intensities and we found higher tussock grasses abundance at intermediate grazing intensity, positively related to litter cover, and negatively to soil organic matter and to bare soil cover. Intense disturbance, and competition with other species could explain its decrease at both grazing extremes. Grazing affected the functional group composition along gradient, but not the total plant cover, species diversity, richness, soil nutritional quality, litter cover, nor bare soil cover. The stability of the ecosystem functions may be supported by the species replacement taking place along the grazing gradient, which keeps constant the total plant cover: the ruderal species dominate heavily grazed sites, the tussock grasses dominate sites under moderate grazing, and a mix of ruderals, tussock grasses and palatable species occupy low grazed sites.