Factors affecting efficacy of prescribed fire for western juniper control

Authors: Clark, Pat; Williams, Christopher - Jason; Pierson Jr, Frederick

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2018
Publication Date: 3/19/2018
Citation: Clark, P., Williams, C.J., Pierson, F.B. 2018. Factors affecting efficacy of prescribed fire for western juniper control. Rangeland Ecology and Management. 71(3):345-355. https://doi.org/10.1016/j.rama.2018.02.002.
DOI: https://doi.org/10.1016/j.rama.2018.02.002

Interpretive Summary: Control of encroaching western juniper (Juniperus occidentalis) is often necessary and important but a lack of fire-efficacy models makes planning of prescribed-fire treatments more difficult and imprecise. Fire-efficacy models were evaluated for prescribed fire in early-successional (Phase I) juniper encroachments on sagebrush-grass rangeland. A simple, 4-variable model accurately predicted juniper mortality rates using only prefire field and GIS information. This fire-efficacy model will help natural resource manager make better informed decisions when planning prescribed-fire treatments.

Technical Abstract: Western juniper (Juniperus occidentalis Hook.) is a tree species occurring on 3.6 million ha in the northern Great Basin. This native species can be quite invasive, encroaching into sagebrush-grassland vegetation, forming woodlands, and dominating extensive landscapes. Control of encroaching juniper is often necessary and important. Efficacy of prescribed fire for western juniper control depends on many factors for which our understanding is still quite incomplete. This knowledge gap makes fire management planning for western juniper control more difficult and imprecise. Natural resource managers require a fire efficacy model which accurately predicts juniper mortality rates and is based entirely on predictors which are measurable prefire. We evaluated efficacy models using data from a fall prescribed fire conducted during 2002 in southwestern Idaho on mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) rangelands with early to mid-successional juniper encroachment. A logistic regression model, which included vegetation cover type, tree height, fire type, and bare ground as predictors, accurately predicted (AUC = 0.881 ± 0.128 SD) the mortality rate for a random sample of western juniper trees marked and assessed prefire and 5 years postfire. Trees occurring in an antelope bitterbrush (Purshia tridentata [Pursh] DC.) type were 8 times more likely to be killed by fire than trees in a mountain big sagebrush type. Probability of mortality decreased by 28.8% for each 1-meter increase in tree height. Trees exposed to head fire were 3 times as likely to be killed as those exposed to backing fire. Interestingly, for each unit increase in bare ground, the probability of mortality increased by 2.31%. Findings from this case study suggest that with just four factors which are readily quantifiable prefire, managers can accurately predict juniper mortality rate and thus make better informed decisions when planning prescribed fire treatments.