Consumers Working Group

How has the aspen leaf miner varied in abundance during its extended outbreak over the past 20 years? How has this affected aspen trees in Interior Alaska?

Alaska’s boreal forest is experiencing an ongoing outbreak of the aspen leaf miner, a small moth. Aspen leaf miner larvae feed only on a single, outer cell layer of the leaf. Despite the limited extent of the leaf tissue damage it causes, this herbivore has wide-ranging physiological effects on aspen trees, slowing tree growth and increasing mortality. At a leaf level, mining damage reduces photosynthesis and increases water loss. Ongoing work is exploring the role of leaf mining on aspen’s ability to manage critical nutrients. In particular we are asking whether leaf mining compromises the tree’s ability to reclaim and store nutrients such as nitrogen from leaves as they senesce in autumn.

We have monitored aspen leaf damage at fine scales for 19 years. We are currently using that long-term data set to better understand the mechanisms that have allowed this outbreak to persist. We have modelled the relative influence of insect population dynamics, natural enemies, plant traits, and environmental conditions on annual levels of leaf damage. Our results indicate that population processes, such as survival to adulthood in the previous year, are the dominant drivers of herbivory, while predators and abiotic factors play more limited roles. Aggressive and often lethal competition among larvae within leaves limits leaf damage and preserves leaf function, likely prolonging the outbreak. These findings highlight the importance of fine-scale biological processes in structuring patterns of forest damage in aspen stands in Interior Alaska.

What factors affect aspen susceptibility to running canker disease?

An emerging fungal pathogen (Neodothiora populina) has been causing widespread mortality in trembling aspen in Alaska. Together with partners in the Bureau of Land Management, National Park Service, and U.S. Forest Service, we are assessing how the presence of the disease is changing across Alaska. Initial findings indicate that mortality in aspen due to the disease remains high.

In order to understand how aspen may resist or succumb to this canker disease, we are actively investigating aspen’s genetic response to the fungal infection and how it is impacted by other stressors due to leaf miner herbivory (carbon and water stress) and drought due to climate change. So far aspen shows a strong genetic response to aspen running canker with large differences in gene expression in smaller- versus larger-diameter trees. Plant metabolic pathways showing changes in gene expression include those involved in pathogen recognition, reinforcing structural barriers (which may help wall off the disease), as well as plant hormone production.

Curious about aspen leaf miner?

• Boyd, M.A., Berner, L.T., Foster, A.C., Goetz, S.J., Rogers, B.M., Walker, X.J., and Mack, M.C. 2021. Historic declines in growth portend trembling aspen death during a contemporary leaf miner outbreak in Alaska. Ecosphere, 12 (6). 085010. https://doi.org/10.1002/ECS2.3569
• Boyd, M.A., Berner, L.T.,, Doak P., Goetz S.C., Rogers B.M., Wagner D., Walker X.J. and Mack M.C. 2019. Impacts of climate and insect herbivory on productivity and physiology of trembling aspen (Populus tremuloides) in Alaskan boreal forests. Environmental Research Letter 14(8)doi:10.1088/1748-9326/ab215f
• Doak P., Wagner D. 2015. The role of interference competition in a sustained population outbreak of the aspen leaf miner in Alaska. Basic and Applied Ecology 16(5): 434-442. https://doi.org/10.1016/j.baae.2015.04.001.
• Wagner D., Wheeler J.M., Burr S.J. 2020. The leaf miner Phyllocnistis populiella negatively impacts water relations in aspen. Tree Physiology. 40(5):580-590. doi: 10.1093/treephys/tpz109. PMID: 31728531

Curious about the aspen running canker disease and the fungal pathogen?

• Ruess R.W., Winton L.M., Adams G.C. 2021. Widespread mortality of trembling aspen (Populus tremuloides) throughout interior Alaskan boreal forests resulting from a novel canker disease. PLoS One. 16(6):e0253996. doi: 10.1371/journal.pone.0253996
• Winton, L. M., Adams, G. C., and Ruess, R. W. 2022. Determining the novel pathogen Neodothiora populina as the causal agent of the aspen running canker disease in Alaska. Canadian Journal of Plant Pathology, 44(1), 103–114. https://doi.org/10.1080/07060661.2021.1952487
• Schütte U.M.E., Wages M., Buechlein A., Kovash J.P., Wrenn D.C., Smrhova T., Zubrova A., Rusch D.B., Winton L.M., Adams G.C., Ruess R.W., Leigh M.B., Drown D.M. 2025. Draft Genome data including functional annotation of an emerging fungal pathogen Neodothiora populina causing a canker disease of trembling aspen in Interior Alaska. PhytoFront. 5(1):90-93. doi:10.1094/PHYTOFR-09-24-0101-A

What is the role of climate in shaping how plant consumers affect tree growth and forest communities?

Despite variability in the abundance of aspen leaf miner from year to year, our analysis of leaf miner damage to aspen leaves during the past two decades suggests a relatively minor role of climate in shaping leaf miner abundance and impacts on leaves. Ongoing work suggests a modest negative relationship between leaf mining damage and both the duration of deep winter cold and the duration of relatively warm periods between snow-out and budbreak. In addition, leaf miner impacts may interact with climate by increasing the vulnerability of aspen to drought stress.