Plant Physiological and Hydraulic Data for Subalpine Fir Infested with Balsam Woolly Adelgid, Idaho and Utah

Since the 1950’s balsam woolly adelgid (Adelges piceae) has been infesting true fir species (Abies sp.) within the Northwestern United States. Balsam woolly adelgid infestations within subalpine fir (Abies lasiocarpa) stands have led to the deterioration of tree stands throughout the northern Intermountain Northwest. Currently, there are only a few studies quantifying the physiological impacts of balsam woolly adelgid infestation on subalpine fir trees. Thus it is unclear how subalpine fir morphology and physiology are altered when infested by balsam woolly adelgid, especially at drier and/or warmer edges of subalpine fir’s range. Here, we quantified the impacts of balsam woolly adelgid infestation on whole-tree water relations in subalpine fir, at cellular to whole-tree scales. We hypothesized that tree morphology would be significantly altered in infested trees, and scale with the intensity of infestation. Additionally, we hypothesized that water stress in infested trees would be evident at cellular to whole-tree scales. Finally, we predicted that hydraulic efficiency would decrease as infestation-level increased. We found that morphological traits such as gouting and crown area were not different between trees of varying infestation levels, nor were branch-tip water potentials. However, cell water relations parameters such as osmotic water potential and turgor loss point were more negative compared to values from non-infested trees in the literature. Finally, sapwood- and leaf area-specific hydraulic conductivity in branches in all infested trees were orders of magnitude lower than conductivities reported for healthy trees. Collectively, our findings demonstrate that balsam woolly adelgid has a strong impact on subalpine fir morphology and whole-tree water relations, and provide insights into the mechanisms causing mortality in infested trees.