ARS | Publication request: Stocking rate effects on spatial heterogeneity in vegetation cover in a grazing-resistant grassland

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 2, 2010
Publication Date: N/A

Technical Abstract: Spatial patterns in rangeland vegetation serve as indicators of rangeland condition and are an important component of wildlife habitat. We illustrate the use of very-large-scale aerial photography (VLSA) to quantify spatial patterns in bare soil of the northeastern Colorado shortgrass steppe. Using three pairs of pastures stocked at moderate versus very heavy rates, we detected higher bare soil under very heavy (X = 22.5%) versus moderate stocking (X = 13.5%; P = 0.053), while the coefficient of variation across pastures was lower under very heavy (X = 0.48) versus moderate stocking (X = 0.75; P =.032). The magnitude of spatial autocorrelation was greatest at a 2-m separation distance under both stocking rates (Moran’s I = 0.48 – 0.58). Bare soil still exhibited significant positive spatial autocorrelation across distances of 60 – 120 m under moderate stocking (mean Moran’s I = 0.14), while patchiness at this scale was eliminated under very heavy grazing (mean Moran’s I = -0.05). At scales of 120 – 480 m, we observed no spatial autocorrelation. Means and spatial patterns for bare soil were similar when analyses were restricted to a single dominant ecological site (Loamy Plains), indicating similar variation among versus within ecological sites. Thus, very heavy grazing did not increase bare soil patchiness at any of the scales examined. Our approach demonstrates the utility of VLSA for analyzing interactions between grazing pressure and other landscape features, and highlights the importance of georeferenced sampling across broad scales (pastures) while still testing for potential shifts in patchiness of bare soil at small (< 10 m) scales.