Understory vegetation change following woodland reduction varies by plant community type and seeding status: a region-wide assessment of ecological benefits and risks

Authors: Monaco, Thomas; GUNNELL, K - Utah Division Of Wildlife Resources

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2020
Publication Date: 8/28/2020
Citation: Monaco, T.A., Gunnell, K.L. 2020. Understory vegetation change following woodland reduction varies by plant community type and seeding status: a region-wide assessment of ecological benefits and risks. Plants. 9(9). Article 1113. https://doi.org/10.3390/plants9091113.
DOI: https://doi.org/10.3390/plants9091113

Interpretive Summary: Woodland expansion via the encroachment and infilling of pinyon (Pinus spp.) and juniper (Juniperus ssp.) (P-J) into sagebrush ecosystems in the Intermountain West is well documented and can diminish wildlife habitat value and watershed functioning. To quantify the sources of variability associated with large-scale mechanical P-J reduction treatments (i.e., chaining, mastication, and cutting) on understory shrub and herbaceous vegetation in this region, we assessed pre- and post-treatment restoration using meta-analysis of effect sizes (In[Post/Pre]) for 165 sizes over a 15-year period. Sites were distributed across three ecoregions (Central Basin and Range, Colorado Plateau, Wasatch and Uinta Mountains) with analysis from this study comprising three plant community types dominated by different sagebrush taxa (mountain big sagebrush, Artemisia tridentata ssp. vaseyana; Wyoming big sagebrush, A. tridentata ssp. wyominensis, and black sagebrush, Artemisia nova, A. Nelson) and three woodland successional phases. Pre-treatment vegetation conditions varied significantly for each treatment type, and treatment outcomes were contingent on ecoregion, plant community, type, and woodland successional phase.

Technical Abstract: Woodland expansion via the encroachment and infilling of pinyon (Pinus spp.) and juniper (Juniperus spp.) (P-J) into sagebrush ecoystems in the Intermountain West is well documented and can diminish wildlife habitat value and watershed functioning. To quantify the sources of variability associated with large-scale mechanical P-J reduction treatments (i.e., chaining, mastication, and cutting) on understory shrub and herbaceous vegetation in this region, we assessed pre- and post-treatment restoration using meta-analysis of effect sizes (In[Post/Pre]) for 165 sites over a 15-year period. Sites were distributed across three ecoregions (Central Basin and Range, Colorado Plateau, Wasatch and Uinta Mountains) with analysis from this study comprising three plant community types dominated by different sagebrush taxa (mountain big sagebrush, Artemisia tridentata ssp. vaseyana; Wyoming big sagebrush, (A. tridentata ssp. wyomingensis, and black sagebrush, Artemisia nova A. Nelson) and three woodland successional phases. Pre-treatment vegetation conditions varied significantly for each type, and treatment outcomes were contingent on ecoregion, plant community type, and woodland successional phase. Perennial grasses increased for all comparisions, especially for chained sites with the highest tree dominance. Perennial forbs also increased in most situations except in cutting treatments and at sites with high initial values and low conifer density. Sagebrush increased in most cases except within Wyoming big sagebrush (A. tridentata ssp. wyomingensis) communities treated with chaining or cutting or when mastication was applied at sites with low initial conifer density. In addition, post-treatment seeding greatly enhanced both shrub and herbaceous perennial vegetation components on masticated sites. This assessment will better inform current management efforts within this region and assist in the development of management guidelines that incorporate site-specific criteria when considering how P-J reduction influences ecosystem services and potential ecological risks.