Moderate disturbances and shrub protection enhance perennial grass recruitment in northern Patagonia

Abstract

Herbivory and fire promote changes in vegetation patches of arid environments, and recruitment plays a key role in their maintenance. We studied seedling dynamics in seven sites with different land use histories related to grazing and fire in north-eastern Patagonian Monte, Argentina. We selected shrub patches in grazed/burned areas. On each shrub patch, we established seven microsites along an under-canopy windward/leeward transect. Seedling recruitment of perennial grasses (PGR) and annual species (ASR) were registered on each microsite. PGR was higher in sites with low-intensity disturbances, and lower in those severely disturbed or not disturbed. PGR was similar on the leeward side, suggesting that shrubs generate similar microsites for their establishment on that side whatever the surrounding disturbance. Severe disturbances promoted non-native ASR. PGR overall was low and apparently, conditions that enhanced ASR also decreased PGR. This situation leads to the replacement of a native-dominated community to one dominated by non-native AS. Our findings suggest that vegetation cover in heavily grazed sites in this semiarid region are sustained mainly by grass re-sprouting capacity, as recruitment is scarce. In contrast, sites that have a fire background and/or are ungrazed show higher PGR, especially in under-canopy microsites.