Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Michael J. Jenkins

Committee

Michael J. Jenkins

Committee

Ted Evans

Committee

Justin Runyon

Abstract

Bark beetle outbreaks have affected millions of hectares of forests across western North America and are a major concern for forest managers. Aside from causing extensive tree mortality, other associated changes include alterations to forest structure in terms of modifications of surface and aerial fuels, which have led to concerns about overall forest health and wildfire risk. The majority of research into the interactions between bark beetles, fuels, and wildfire, has focused on upper elevation forests primarily in lodgepole pine and Engelmann spruce. Little research has been led in lower to middle montane forests which typically are more structurally and compositionally diverse, and often more fuel limited, which could have strong impacts on fire in these types of forests infested by bark beetles. Additionally, the few studies to have addressed this issue, strictly confined their research to characterizing changes to fuel loads or stand structural conditions. The purpose of this research was to quantify changes to surface and canopy fuels in middle montane interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) forests infested by Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins), while also measuring physical and chemical changes to foliage in terms of moisture content and terpenes which has yet to be reported in current literature.

Study results indicated the most substantive changes were found in canopy fuels where significant reductions in foliar moisture were measured as tree foliage transitioned from green (non-infested) phase to red (2-3 year post infested) phase. During this period emissions and concentrations of terpenes associated with elevating foliage flammability increased and peaked in trees exhibiting a yellow or red crown. This could have important implications for raising the threshold for crown fire initiation in conjunction with suitable fire weather conditions. Following the red crown phase, trees shed their needles leading to significant reductions in canopy bulk density (measure of the amount of fuel in the canopy of a stand), and a decreased canopy base height (average height of canopy fuel above the forest floor across a stand), which would likely lead to a reduction in crown fire potential.

Overall, this study contributes to the growing body of literature in assessing bark beetle fuel interactions by providing evidence of physical and chemical changes to tree foliage following infestations by Douglas-fir beetle. Furthermore, the inherent variable structure, composition, and mixed-severity fire regime characteristic of interior Douglas-fir forests presents a challenge for creating a blanket description of how these forests will react in terms of fuel changes following bark beetle infestations. Additional fuel studies concentrated in interior Douglas-fir stands in other geographic locales throughout the central Rocky Mountains will help further expand knowledge in regards to bark beetle induced modifications to fuels throughout the lower to middle montane zone.

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