Year of Award

2017

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Forest and Conservation Science

Other Degree Name/Area of Focus

Silviculture

Department or School/College

College of Forestry and Conservation

Committee Chair

Christopher R. Keyes

Commitee Members

David L. R. Affleck, Andrew J. Larson, Sharon M. Hood, Anna Sala

Abstract

Land management agencies across the western U.S. have urgently sought to restore forests with non-stand-replacing fire regimes to facilitate stand resistance to crown fire. Although silvicultural restoration has been shown to immediately reduce the probability of widespread crown fire, little is known about the mid- to long-term impacts of restoration on vegetation, fuel, and crown fire hazard development. This study examined mid-term (10-14 years) experimental restoration treatment effects in two different non-stand-replacing fire regimes: a frequent, low-severity regime, and an infrequent, mixed-severity regime. Restoration of frequent, low-severity fire regime was represented by fuel reduction treatments in the ponderosa pine/Douglas-fir forest type, whereas restoration of infrequent, mixed-severity fire regime was represented by retention harvesting in the lodgepole pine forest type. After restorative fuel reduction treatments, the experimental ponderosa pine/Douglas-fir stands were also impacted by mountain pine beetle outbreak. The combined effects of fuel reduction and beetle outbreak in these stands resulted in forest structure that converged across treatments for many ecological and fuel attributes, though thinning and burning together demonstrated the greatest treatment longevity. Retention harvesting in lodgepole pine created variable canopy conditions that affected growth and reduced the probability of crown fire spread, but treatment increased surface fireline intensities and susceptibility to torching. Overall, this study highlights that stands treated to restore resistance to crown fire change in structure and fire hazard over time due to overstory mortality and understory growth.

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© Copyright 2017 Justin Seth Crotteau