Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Forestry (MS)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Tara Bal

Committee Member 1

Julia Burton

Committee Member 2

Christopher Webster


Sugar maple (Acer saccharum) is a foundational tree species in northern hardwood forests of the United States and Canada. Though previous work has documented areas of substantial stress for this species in eastern North America, increasing reports of crown dieback in the Upper Great Lake states through the early 2000’s highlighted the relative lack of understanding of regional trends and causes. A 120-plot network of maple forest health monitoring sites was established and annually visited across Upper Michigan, northern Wisconsin, and eastern Minnesota between 2009 and 2012 to catalog and understand the regional phenomenon.

Results from the project’s initial years (Phase I) determined a significant correlation between sugar maple dieback and interrelated forest floor conditions (earthworm impact rating, soil carbon, herbaceous cover, and soil manganese) known to be influenced by exotic earthworms.

Ten years later, the network was resurveyed in 2021 and 2022 (Phase II). Sampling methods replicated prior methodology and added additional damaging agent signs and symptoms, including ungulate browse, lecanium species (Parthenolecanium spp.) and cottony maple scale (Pulvinaria innumerabilis), as well as more detailed sampling of earthworm species abundance, diversity, and impact.

Resurvey data suggest earthworm impact rating is still significantly correlated with sugar maple dieback across the network. Sugar maple dieback is ongoing and is 15.4% per tree averaged at the plot level (compared with 12.4% ten years ago) across the study area, though it is highly variable. Also, average canopy dieback for residual trees in harvest treatments worsened over the intervening years. Scale are not apparently linked to dieback condition. Future uses for the data include amendment of risk maps that land managers can incorporate into treatment plans using key correlates of decreased sugar maple health and vigor.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.