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.