Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources

Committee Chair(s)

R. Justin DeRose


R. Justin DeRose


Diane G. Alston


Barbara J. Bentz


The balsam woolly adelgid (BWA), is an invasive forest insect native to central and southern Europe. In 2017, it was detected in Utah for the first time. While BWA had limited impact as a pest in its native European range, it has caused considerable damage to true fir populations in North America. In the Intermountain region, subalpine fir has been identified as the tree species most at risk of BWA infestation. Subalpine fir provides a variety of ecosystem services and is a critical component of the spruce-fir alpine forests of the area. With an expected increase in the severity and impact of BWA to the forests of the Intermountain region, a study was undertaken to investigate ecological factors influencing BWA's impact and apply that knowledge to predict future impact.

To accomplish this, over forty research plots were established across Utah and southeastern Idaho in BWA-infested areas. Data on various aspects of trees and stands, including tree size, observed damage and health of the trees, forest community composition, stand structure, and abiotic factors were collected. The aim was to understand the relationships between these factors and the severity of BWA infestations. Additionally, the occurrence data of other pests affecting subalpine fir were gathered to explore potential interactions within the "subalpine fir mortality complex.” The study yielded significant findings. Firstly, it provided an assessment of recent BWA infestations within Utah and southern Idaho, estimating the severity and mortality levels caused by the insect. Secondly, the analysis of forest characteristics revealed crucial insights. It highlighted the importance of forest structure in influencing the severity of BWA infestations. Moreover, the study shed light on the previously unexplored interactions between BWA and other pests affecting subalpine fir. These findings were then used in the creation of a hazard rating system for categorizing forests within the study area into risk levels based on forest and climate characteristics.