From the NPS:
Depriving western old-growth forests of fire brought them to the brink. Now the fire they need also threatens them. To fix this, parks are returning to mechanical forestry methods.
“As shown by our pilot study, in these situations, mechanical thinning can mimic some effects of prescribed fire. This is increasingly supported by science, which has demonstrated that thinning can reduce air quality impacts, increase water yield, reduce tree stress, and improve tree health. The goals of these thinning treatments are to retain and recruit old-growth and large, vigorous, mature trees and allow the subsequent use of low-intensity prescribed fire to maintain the stand in perpetuity.”