RELATION BETWEEN NOAA-AVHRR SATELLITE DATA AND STOCKING RATE OF RANGELANDS

Abstract

Biomass of both wild herbivores and livestock in rangelands is correlated with rainfall at a regional scale. Thus, rainfall may be a good predictor of actual stocking rates. However, rainfall data are scarce in many regions, and their spatial resolution is usually much coarser than needed to set or to evaluate wildlife or livestock stocking rates. We here show a relationship between livestock biomass and an annual vegetation index (normalized-difference vegetation index-integrated value, NDVI-I) calculated from remotely sensed data on spectral properties of rangelands of Argentina. The relationship is as strong or even stronger than previously reported correlations between herbivore biomass and rainfall. This, together with the greater availability and higher spatial resolution of satellite data, makes remote sensing a potentially valuable tool to predict stocking rates for regions, landscapes, and different portions of a landscape. The form of the relationship between stocking rate and average NDVI-I was exponential, which, as previously shown, indicates an increasing herbivore load per unit of primary production as rainfall or productivity increases. This may be at least partially explained by the fact that the NDVI interannual variation and seasonality were negatively related with average NDVI-I. Thus, stocking rate may increase exponentially because of an increasing year-to-year reliability of the forage resource and a more even distribution within the year.