Comparing changes in fuel loading, tree regeneration, and forest structure in once- and twice-burned mixed-conifer forests with a before-after-control-impact case study in the Bob Marshall Wilderness

Author

Wyatt W. Trull, University of Montana, MissoulaFollow

Graduation Year

2017

Graduation Month

May

Document Type

Thesis

Degree Name

Bachelor of Science – Forestry

School or Department

Forestry and Conservation

Major

Forestry – Forest Resources Management

Faculty Mentor Department

Forestry and Conservation, College of

Faculty Mentor

Andrew Larson

Keywords

Fuel Loading, Mixed-conifer forests, wildfire, Bob Marshall Wilderness, forest structure, disturbance ecology

Subject Categories

Natural Resources and Conservation | Natural Resources Management and Policy | Other Environmental Sciences

Abstract

Wildfires drive landscape character in the seasonally dry mixed-conifer forests of western North America. Forested landscapes in this region are a mosaic of overlapping burn perimeters, which span a wide gradient of severity and burn age. The goal of this study was to compare the effects of single and repeat wildfires on fuel loading and forest structure and composition. Our study site spans the east and west sides of the South Fork of Flathead River in the Bob Marshall Wilderness. The east side of the river burned in 2000 in the Helen Creek Fire. The west side of the river burned in 2003 in the Little Salmon Complex. Data was collected in 2011. In 2013, the east side of the river burned again, but the west side of the river did not burn a second time. In 2015, plots on both the east and west side of the river were resampled. Between 2011 and 2015, mean coarse woody debris load (>7.6 cm diameter) in twice-burned plots decreased by 23%, while once-burned plots increased by 76%. Total mean fine woody debris (<7.6 cm diameter) decreased by 30% in twice-burned plots and increased by 80% in once-burned plots. These changes in woody debris are the net outcome of inputs from standing dead trees that fell between 2011 and 2015 (including branch fall) and outputs from combustion and decomposition. For both once- and twice-burned plots, the density of live trees changed very little between measurements, but the density of dead trees significantly decreased. The density of dead western larch saplings and seedlings tended to be greater on twice-burned plots. The once- or twice-burned variable has a strong effect on surface fuels and tree regeneration, but a weak effect on forest structure and composition. The results of this study suggest that shorter fire return intervals lead to lower surface fuel load and more fire-tolerant forest structure and composition.

Honors College Research Project

1

Recommended Citation

Trull, Wyatt W., "Comparing changes in fuel loading, tree regeneration, and forest structure in once- and twice-burned mixed-conifer forests with a before-after-control-impact case study in the Bob Marshall Wilderness" (2017). Undergraduate Theses, Professional Papers, and Capstone Artifacts. 127.
https://scholarworks.umt.edu/utpp/127