Document: ROB-3-65-29

How does a sagebrush steppe landscape's composition and pattern respond to grazing, fire, and climate change?

WASHINGTON-ALLEN, R.A.* ^1,2, N.E.WEST ¹, R.D.RAMSEY ³ and C.T.HUNSAKER ^1,4

Utah State University, Logan, Utah 84322-5230 USA ¹
Oak Ridge National Laboratory, MS 6407, Oak Ridge, TN 37831-6407 USA ²
Remote Sesnsing/GIS Laboratory, Logan, Utah 84322-5240 USA ³
USDA Forest Service, Fresno, CA 93710 USA ⁴

Abstract:
Simulated landscapes, which contained small proportions of shrubs relative to higher equal proportions of grass and baresoil, were subjected to both high drought frequency and grazing and low drought frequency and high grazing disturbance regimes. Faster canopy cover convergence to shrub dominance, grass cover extinction, and increased clumping of shrub patches occurred in the landscapes treated by high drought frequency and high grazing regimes. We wondered: Do real landscapes, which are subject to grazing, fire, and climate change, respond in a similar manner? We tested these hypotheses on a sagebrush steppe landscape which was subject to mixed-commercial grazing (livestock and wildlife), fire, and, drought. We hypothesized that both shrub and bare soil cover would be greater relative to grass with a decrease in grass cover, high clumping of shrub, and high interspersion of grass. We generated a timeseries (1972 to 1997) of plant growth form and land cover images, i.e., shrub, grass, and baresoil, from 22 dry season Landsat satellite images. We found 1) shrub cover became greater than grass cover in 1974 with a corresponding decrease in grass cover; 2) shrub patches became more clumped, but patches were smaller in size and thus more fragmented; 3) from 1972 to 1997 grass patches were highly dispersed, became smaller in size, but number of patches remained constant, and 4) baresoil became fragmented, where cover did not change, mean patch size became smaller and increased in number. Increase in the number of cattle grazing the landscape over time appears to be the primary driver behind these changes rather than climate change.

Keywords: Critical Threshold, Remote Sensing, timeseries, Two-phase Mosaic

This abstract is being presented at: 11:30 AM in session:
Oral Session #22: Multiple Disturbance Effects, Including Fire.