Year of Award
2023
Document Type
Thesis
Degree Type
Master of Science (MS)
Degree Name
Forestry
Department or School/College
W.A. Franke College of Forestry & Conservation, Department of Forest Management
Committee Chair
John Goodburn
Commitee Members
Diana Six, Beth Dodson, Zachary Holden
Keywords
bark beetles, outbreaks, ponderosa pine, weather
Subject Categories
Entomology | Forest Biology
Abstract
Bark beetles are a diverse family of insect herbivores, of which the most aggressive species can cause significant tree mortality, and are integral components of disturbance regimes in conifer dominated forests of North America. Recent drought events across the western U.S. have been broadly associated with the initiation of multiple bark beetle outbreaks in ponderosa pine forests during the last two decades. Changing weather conditions, such as those observed during the onset of drought, affect outbreak progression through their influence on bark beetle physiology and life history traits and the overall vigor and defensiveness of host trees. This study used bark beetle-caused forest mortality estimates collected from aerial observations and climate data to understand the effects of weather on the intensification and collapse of outbreaks that occurred in ponderosa pine forests across the Northern Rocky Mountains (2003-2014) and the Black Hills (2006-2017). We found that declining precipitation totals and increasing temperatures were associated with a higher likelihood of bark beetle outbreaks intensifying within watersheds across both study areas. Outbreak collapse in the Black Hills was facilitated by the return of adequate precipitation levels, likely restoring the defensive capacity of ponderosa pine to resist further beetle colonization. Weather conditions did not facilitate outbreak collapse in the Northern Rocky Mountains as warm, dry conditions favorable to outbreak development persisted across the region. Instead, declining bark beetle populations observed in lodgepole pine forests appear to have increased the likelihood of collapse in adjacent ponderosa pine forests. These results improve our understanding of bark beetle population ecology as it relates to weather at a landscape scale and can be critical for forest health monitoring efforts in anticipating the potential development of future irruptions when increased bark beetle activity across a region is detected.
Recommended Citation
Lestina, Jordan T., "THE EFFECTS OF WEATHER ON FACILITATING THE INTENSIFICATION AND COLLAPSE OF BARK BEETLE OUTBREAKS IN PONDEROSA PINE FORESTS OF THE NORTHERN ROCKY MOUNTAINS AND THE BLACK HILLS" (2023). Graduate Student Theses, Dissertations, & Professional Papers. 12245.
https://scholarworks.umt.edu/etd/12245
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© Copyright 2023 Jordan T. Lestina