Plant and soil consequences of shrub management in a big sagebrush-dominated rangeland ecosystem

Authors: Derner, Justin; SCHUMAN, GERALD - Collaborator; Follett, Ronald; VANCE, GEORGE - University Of Wyoming

Submitted to: Environment and Natural Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2013
Publication Date: 1/7/2014
Citation: Derner, J.D., Schuman, G.E., Follett, R.F., Vance, G. 2014. Plant and soil consequences of shrub management in a big sagebrush-dominated rangeland ecosystem. Environment and Natural Resources Research. 4(1):19-30.

Interpretive Summary: Sagebrush is a long-lived shrub that is prominent on many western US lands that have low rainfall. The influence of different management practices on this shrub have been evaluated over many years with regards to increasing forage production of the grasses that grow in plant communities with sagebrush, but how soil carbon is influenced by these shrub management practices has not received attention. We evaluated the responses of soil organic carbon in study sites in southwestern Wyoming to two different shrub management practices: mowing and a targeted herbicide that selectively reduces sagebrush. Although mowing did not affect soil organic carbon, using the targeted herbicide did increase soil carbon as the density (number of plants per unit area) of sagebrush plants was reduced and perennial grasses increased.

Technical Abstract: Soil organic carbon (SOC) responses to shrub management in western US rangelands, especially those dominated by Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) in low rainfall areas (<300 mm), remains a major knowledge gap. We sampled vegetation and soils in 2009 from two contrasting ecological sites: 1) Sandy with 190 mm mean annual precipitation (SES), and 2) Loamy with 263 mm mean annual precipitation (LES), in southwestern Wyoming using paired sets of shrub management treatments. We compared treatments in SES that were 1) mowed to 10 cm height in 2002 or 2) not mowed. At the LES, we compared treatments that were: 1) mowed to a 10 cm height in 1997, 2) herbicided with Spike® 20P (tebuthiuron) in 1997, or 3) not mowed or herbicided. Consistent vegetation responses to mowing at the SES and LES were observed through 1) no effects on live big sagebrush plant density, 2) three- to four-fold increases in dead sagebrush plant densities, 3) reduced sagebrush height, 4) increased cover of perennial grasses, 5) reduced cover of big sagebrush, and 6) no effects on bare ground. Vegetation responses to the herbicide application were similar to mowing in the LES with the notable exceptions of 1) substantially lower densities of live sagebrush plants and 2) taller live shrubs. Mowing did not affect SOC for either SES or LES. However, herbicide application at the LES increased SOC in both the 0-5 (43% increase) and 5-15 (17% increase) cm depth increments, corresponding to annual soil C sequestration rates of 0.16 and 0.14 Mg C ha-1 yr-1 for the 0-5 and 5-15 cm soil depths, respectively. Shrub treatments in sagebrush-dominated rangelands can markedly affect vegetation responses but increases in SOC through shrub management occur when density of Wyoming big sagebrush plants is reduced.