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Mowing Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) Cover Effects Across Northern and Central Nevada

Author:
Swanson, Sherman R., Swanson, John C., Murphy, Peter J., McAdoo, J. Kent, Schultz, Brad
Source:
Rangeland ecology & management 2016 v.69 no.5 pp. 360-372
ISSN:
1550-7424
Subject:
Artemisia tridentata subsp. wyomingensis, Bromus tectorum, annuals, forbs, grasses, mosses and liverworts, mowing, perennials, risk, soil, wildfires, Nevada
Abstract:
Many Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis) communities are invaded by exotic annuals, especially cheatgrass (Bromus tectorum L.), promoting larger and more frequent wildfires. Mowing sagebrush can reduce fire risk. To identify community features favoring regeneration of native perennials over exotic annuals, we compared paired, adjacent unmowed and mowed areas treated between 2001 and 2010 at 76 sites across northern and central Nevada. We quantified soil surface and foliar cover in 12 cover groups, as well as slope, aspect, elevation, and time since mowing (0−10 years). We identified unmowed cover characteristics and site covariates that best predicted herbaceous cover in mowed areas and differences in herbaceous cover between adjacent mowed and unmowed areas. Mowed areas had significantly (P < 0.01) more absolute cover (%) of litter (14.6), perennial grasses (4.9), cheatgrass (2.0), and exotic forbs (1.1) and less sagebrush (−13.5), bare soil (−11.4), moss (−3.3), and rock (−0.8) than adjacent unmowed areas. Except for sagebrush, all cover group values were correlated between unmowed and mowed areas. The “perennial balance” (perennial minus annual herbaceous cover) was positive at 75% (57) of mowed areas and increased from unmowed to mowed areas at 51 sites. A positive perennial balance in mowed areas was more likely where paired unmowed areas lacked cheatgrass, had greater cover of perennial grass, and less of exotic forbs. Likewise, sites whose unmowed areas had > 30% sagebrush cover consisting of smaller plants had larger gains in perennial balance from unmowed to mowed areas. An increase in perennial balance from unmowed to mowed areas was more likely in central and northeastern Nevada and at sites mowed more recently. To encourage perennial grasses over annual herbaceous species in Wyoming big sagebrush communities, mowing is better suited to locales lacking exotic annuals and retaining ample cover of perennial grasses and sagebrush of smaller size.
Agid:
5271640