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Wildfire activity is increasing in boreal forests as climate warms and dries, increasing risks to rural and urban communities. In black spruce forests of Interior Alaska, fuel reduction treatments are used to create a defensible space for fire suppression and slow fire spread. These treatments introduce novel disturbance characteristics, making longer-term outcomes on ecosystem structure and wildfire risk reduction uncertain. We remeasured a network of sites where fuels were reduced through hand thinning or mechanical shearblading in Interior Alaska to assess how successional trajectories of tree dominance, understory composition, and permafrost change over ∼ 20 years after treatment. We also assessed if these fuel reduction treatments reduce modeled surface rate of fire spread (ROS), flame length, and fireline intensity relative to an untreated black spruce stand, and if surface fire behavior changes over time. In thinned areas, soil organic layer (SOL) disturbance promoted tree seedling recruitment but did not change over time. In shearbladed sites, by contrast, both conifer and broad-leaved deciduous seedling density increased over time and deciduous seedlings were 20 times more abundant than spruce. Thaw depth increased over time in both treatments and was greatest in shearbladed sites with a thin SOL. Understory composition was not altered by thinning but in shearbladed treatments shifted from forbs and horsetail to tall deciduous shrubs and grasses over time. Modeled surface fire behavior was constant in shearbladed sites. This finding is inconsistent with expert opinion, highlighting the need for additional fuels-specific data to capture the changing vegetation structure. Treatment effectiveness at reducing modeled surface ROS, flame length, and fireline intensity depended on the fuel model used for an untreated black spruce stand, pointing to uncertainties about the efficacy of these treatments at mitigating surface fire behavior. Overall, we show that fuel reduction treatments can promote low flammability, deciduous tree dominated successional trajectories, and that shearblading has strong effects on understory composition and permafrost degradation that persist for nearly two decades after disturbance. Such factors need to be considered to enhance the design, management, and predictions of fire behavior in these treatments.
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This content will become publicly available on October 22, 2026
Do fuel reduction treatments in Alaska affect tree health?
Abstract Increasing wildfire risk in Alaska has prompted the adoption of fuel reduction treatments, including hand-thinning and mechanical mastication, to mitigate fire behavior and improve firefighter safety. These fuel treatments may influence tree health conditions, including mortality, wind damage, disease, and one of the most wide-spread health threats to these forests, bark beetle infestations. Here, we compared fuel reduction treatments with paired untreated stands to estimate their effects on adverse tree health conditions, surveying 33 sites across two regions in Alaska experiencing endemic and outbreak levels of spruce beetle infestation. Our results show that fuel reduction treatments, particularly hand-thinning, reduced the density of dead trees and did not significantly increase wind damage, disease, or bark beetle infestation. However, there were two exceptions: in the outbreak region, trees along the edges of masticated treatments had a higher probability of (1) disease and (2) northern spruce engraver presence than trees in untreated stands. Overall, our findings suggest that fuel reduction treatments reduce hazardous dead trees without sacrificing the health of the remaining trees, providing support for fuel reduction treatments as a low-risk strategy for wildfire management.
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- Award ID(s):
- 2127284
- PAR ID:
- 10651082
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- Environmental Research: Ecology
- Volume:
- 4
- Issue:
- 4
- ISSN:
- 2752-664X
- Page Range / eLocation ID:
- 045002
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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