Disturbance type and sagebrush community type affect plat community struction following shrub reduction

Authors: RIGINOS, CORINNA - Nature Conservancy; VEBLEN, K - Utah State University; THACKER, E - Utah State University; GUNNELL, KEVIN - Utah Division Of Wildlife Resources; Monaco, Thomas

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2019
Publication Date: 6/20/2019
Citation: Riginos, C., Veblen, K.E., Thacker, E.T., Gunnell, K., Monaco, T.A. 2019. Disturbance type and sagebrush community type affect plat community struction following shrub reduction. Rangeland Ecology and Management. 72(4):619-631. https://doi.org/10.1016/j.rama.2019.01.007.
DOI: https://doi.org/10.1016/j.rama.2019.01.007

Interpretive Summary: Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and towards shrub and perennial grass co-dominance. In sagebrush (Artemisia spp.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah's Watershed Restoration Initiative (WRI) project to assess short-term (1-5 years post-treatment) and long-term (6-12 years post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites spanning a range of abiotic conditions and sagebrush community types. Treatments were: Dixie pipe harrow with one or two passes, Lawson aerator, and fire with and without post-fire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short- and long-term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata ssp. wyomingenis) communities, but in mountain big sagebrush (ssp. vaseyana) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum) increased in all treatments in sites dominated by mountain big sagebrush but stayed constant or decreased in sites dominated by Wyoming big sagebrush; this was surprising given that sites dominated by Wyoming big sagebrush are typically thought to have lower resilience to disturbance and resistance to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions about applying such treatments.

Technical Abstract: Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and towards shrub and perennial grass co-dominance. In sagebrush (Artemisia spp.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah's Watershed Restoration Initiative (WRI) project to assess short-term (1-5 years post-treatment) and long-term (6-12 years post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites spanning a range of abiotic conditions and sagebrush community types. Treatments were Dixie pipe harrow with one or two passes, Lawson aerator, and fire with and without post-fire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short- and long-term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata ssp. wyomingenis) communities, but in mountain big sagebrush (ssp. vaseyana) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum) increased in all treatments in sites dominated by mountain big sagebrush but stayed constant or decreased in sites dominated by Wyoming big sagebrush; this was surprising given that sites dominated by Wyoming big sagebrush are typically thought to have lower resilience to disturbance and resistance to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions aboout applying such treatments.