Title

Comparing changes in fuel loading, tree regeneration, and forest structure in once- and twice-burned mixed-conifer forests

Presentation Type

Presentation

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, tree regeneration, and forest structure. Our study site spans the east and west sides of the South Fork of Flathead River in the Bob Marshall Wilderness. Data was collected in 2011, eight years after the initial fire burned both sides of the river. In 2013, the east side of the river burned a second time and 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%. Fine woody debris (<7.6 cm diameter) increased by 12% in twice-burned plots and increased by 184% 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 losses due to combustion and decomposition. Larch seedlings (<1.37 m tall) decreased by 34% in once-burned plots and decreased by 84% in twice-burned plots. The decrease in once-burned plots is primarily due to growth of seedlings into the sapling size class (>1.37 m tall), while the decrease in twice-burned plots is due to fire-caused mortality. The logistical complexity of backcountry travel makes case studies from wilderness areas rare. However, wilderness areas provide an important reference for understanding the role of uninhibited fire in forest ecosystems. This study shows that shorter fire return intervals lead to lower woody debris loads and seedling densities, maintaining forest conditions.

Category

Life Sciences

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Apr 15th, 10:00 AM Apr 15th, 10:20 AM

Comparing changes in fuel loading, tree regeneration, and forest structure in once- and twice-burned mixed-conifer forests

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, tree regeneration, and forest structure. Our study site spans the east and west sides of the South Fork of Flathead River in the Bob Marshall Wilderness. Data was collected in 2011, eight years after the initial fire burned both sides of the river. In 2013, the east side of the river burned a second time and 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%. Fine woody debris (<7.6 cm diameter) increased by 12% in twice-burned plots and increased by 184% 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 losses due to combustion and decomposition. Larch seedlings (<1.37 m tall) decreased by 34% in once-burned plots and decreased by 84% in twice-burned plots. The decrease in once-burned plots is primarily due to growth of seedlings into the sapling size class (>1.37 m tall), while the decrease in twice-burned plots is due to fire-caused mortality. The logistical complexity of backcountry travel makes case studies from wilderness areas rare. However, wilderness areas provide an important reference for understanding the role of uninhibited fire in forest ecosystems. This study shows that shorter fire return intervals lead to lower woody debris loads and seedling densities, maintaining forest conditions.