Climate modulates grazing effects on primary productivity of arid ecosystems in Argentina

Abstract

The introduction of artificial water sources for livestock uses in ecosystems where water has been absent during their evolution has caused changes in vegetation. It has been proven that there is a radial mitigation of grazing impact with the distance between the water sources, which encourages the formation of piospheres. In Argentina, there are no studies that evaluate how climate acts as a modulator of the effects of grazing in piospheres along environmental gradients. The objective of this study was to evaluate and analyze the role that climate plays as a modulator of effects that grazing induces on a local scale. This would allow us to understand how the climate acts on the effects of grazing. For that, 77 piospheres were selected along a climatic gradient that covers arid and semi-arid areas of Argentina and the spatial variability of the NDVI (Normalized Difference Vegetation Index) values in the grazing gradient were analyzed as well as its relationship with mean annual precipitation and mean annual temperature. Two different patterns of NDVI response were observed within the grazing gradient. Pattern 1 presented an increase in NDVI with distance to the water point, while pattern 2 showed a reverse effect. The piospheres of patterns 1 and 2 were located above and below 280 mm of annual precipitation and 14.5 °C of mean annual temperature, respectively. These results suggest that there is a differential effect of grazing on vegetation, and that this effect is modulated by climatic variables.