Grazing effect on NDVI across an aridity gradient in Argentina

Grazing effects on aboveground net primary production (ANPP) have ever been controversial. Certain plant communities are very sensitive to grazing and others are not. We analyzed the grazing effect on ANPP across a gradient of mean annual precipitation (MAP) in rangelands of Central Argentina. We focused not only on the regional patterns of the grazing effect on ANPP but also on the response of the inter-annual variability of ANPP to this disturbance. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a spectral index calculated from the reflectance in the red and infrared portion of the spectrum as recorded by the AVHRR/NOAA sensor as an estimator of ANPP. This variable was recorded at increasing distances from the watering point in large paddock distributed through the MAP gradient (250-600 mm) of the extensive plains Arid Chaco in Argentina. Grazing effect on NDVI decreased along the regional gradient of MAP. The grazing effect on NDVI varied among years, being greater in dry than in wet years. Regional patterns changed among years because the NDVI close to the watering points had high inter-annual variability at the driest extreme of the gradient. Our findings contribute a conceptual framework to grazing management in semi-arid rangeland. Considering that grazing effect on NDVI-I was higher in and than in wet sites implicates that appropriate grazing management strategies would be different in sites with different precipitation levels. (c) 2007 Elsevier Ltd. All rights reserved.