|Hunt, Earle - Ray|
Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2005
Publication Date: 1/26/2006
Citation: Hunt, E.R., Miyake, B.A. 2006. Comparison of stocking rates from remote sensing and geospatial data. Rangeland Ecology & Management. 59:11-18. Interpretive Summary: Remote sensing data from the Advanced Very High Resolution Radiometer (AVHRR) have coarse spatial resolution (1 km2 pixel size) and high temporal resolution, which can be used to estimate net primary production regionally. Net primary production are used to calculate the stocking rate for grazing in animal-unit months per acre (AUM/acre). A stocking rate of 0.5 AUM/acre indicates that two acres of land have sufficient forage available to nourish one mature cow for one month. AVHRR data from 1989 to 2000 were used to map stocking rates for the entire state of Wyoming. Initial stocking rates are also given in Natural Resources Conservation Service Technician Guides for an area based on soil and precipitation data. The stocking rates in the Technician Guides were mapped for the entire state of Wyoming and compared to the stocking rates determined by remote sensing. In general, the same spatial patterns were seen in both maps, which is expected because these two methods are different approaches, using different data sets, to mapping the vegetation. Differences between the two approaches highlight either errors in the data used to make the maps or errors in logic setting the stocking rates. These maps will not help set stocking rates for individual allotments, because the AVHRR pixel size is large (1 square kilometer) and the map scale is coarse (1:500,000) , but the average stocking rate for an area will be correctly determined.
Technical Abstract: Remote sensing data from the Advanced Very High Resolution Radiometer (AVHRR) have coarse spatial resolution (1 km2 pixel size) and high temporal resolution, which can be used to estimate net primary production regionally. The Normalized Difference Vegetation Index (NDVI) is used to determine the fraction of absorbed photosynthetically active radiation, which shows year-to-year variation due to precipitation. The 12-year average of net primary production was used to calculate stocking rates in animal-unit months per acre for the state of Wyoming. Stocking rates were also calculated for Wyoming from 1:500,000 scale soil and climate geospatial data layers and National Resource Conservation Service Technical Guides within a geographic information system. In a pixel-by-pixel comparison, there was a weak but significant correlation between the two methods with similar spatial pattern. There were areas with large divergence, for example high alpine meadows and sub-irrigated soils, where the AVHRR data predicted much lower stocking rates. Whereas the AVHRR pixel size is too coarse for estimating stocking rates for an individual allotment, it does set an upper bound for the region.