To burn or not to burn: Comparing reintroducing fire with cutting an encroaching conifer for conservation of an imperiled shrub-steppe

Authors: Davies, Kirk; Rios, Roxanne; Bates, Jonathan - Jon; JOHNSON, DUSTIN - Oregon State University; KERBY, JAY - Nature Conservancy; Boyd, Chad

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2019
Publication Date: 8/1/2019
Citation: Davies, K.W., Rios, R.C., Bates, J.D., Johnson, D.D., Kerby, J., Boyd, C.S. 2019. To burn or not to burn: Comparing reintroducing fire with cutting an encroaching conifer for conservation of an imperiled shrub-steppe. Ecology and Evolution. 9(16):9137-9148. https://doi.org/10.1002/ece3.5461.
DOI: https://doi.org/10.1002/ece3.5461

Interpretive Summary: Western juniper has encroached and degraded millions of acres of sagebrush steppe. Burning and cutting treatments have been used to control juniper. However, recently a general aversion to burning has developed because it also reduces sagebrush and is thought to increase in exotic annual grasses. We compared cutting with burning applied over the last ~30 years. Burning provided more complete and longer lasting control of juniper compared to cutting. This resulted in longer sagebrush dominance in the burned areas even though sagebrush was initially decreased with burning. Exotic annual grass cover did not differ between treatments, but was greater on hotter and drier sites, especially if they had reduced perennial grass abundance. This information is useful to rangeland and wildlife managers attempting to restore sagebrush steppe communities.

Technical Abstract: Woody vegetation has increased on rangelands worldwide for the past 100–200 years, often because of reduced fire frequency. However, there is a general aversion to reintroducing fire, and therefore, fire surrogates are often used in its place to reverse woody plant encroachment. Determining the conservation effectiveness of reintroducing fire compared with fire surrogates over different time scales is needed to improve conservation efforts. We evaluated the conservation effectiveness of reintroducing fire with a fire surrogate (cutting) applied over the last ~30 years to control juniper (Juniperus occidentalis Hook.) encroachment on 77 sagebrush-steppe sites. Critical to conservation of this imperiled ecosystem is to limit juniper, not encourage exotic annual grasses, and promote sagebrush dominance of the overstory. Reintroducing fire was more effective than cutting at reducing juniper abundance and extending the period of time that juniper was not dominating the plant community. Sagebrush was reduced more with burning than cutting. Sagebrush, however, was predicted to be a substantial component of the overstory longer in burned than cut areas because of more effective juniper control. Variation in exotic annual grass cover was explained by environmental variables and perennial grass abundance, but not treatment, with annual grasses being problematic on hotter and drier sites with less perennial grass. This suggests that ecological memory varies along an environmental gradient. Reintroducing fire was more effective than cutting at conserving sagebrush-steppe encroached by juniper over extended time frames; however, cutting was more effective for short-term conservation. This suggests fire and fire surrogates both have critical roles in conservation of imperiled ecosystems.