Spatial patterns of 19th century fire severity persist after fire exclusion and a 21st century wildfire in a mixed conifer forest landscape, Southern Cascades, USA

Authors: Alan Taylor*, Pennsylvania State University, Catherine Lauvaux, Geography Department Penn State University, Becky Estes, USDA Foreset Service, Lucas Harris, Department of Geography, Penn State, Carl Skinner, USDA Forest Service (retired)
Topics: Biogeography, Environmental Science, Mountain Environments
Keywords: Fire severity, Resilience, Fire exclusion, Topography, Legacy effects, Fire deficit
Session Type: Virtual Paper
Day: 4/7/2021
Start / End Time: 9:35 AM / 10:50 AM
Room: Virtual 9
Presentation File: No File Uploaded

Spatial patterns of fire severity are influenced by fire-vegetation patch dynamics and topography. Since the late 19th century fire exclusion has increased fuels and recent fire severity patterns may diverge from historical patterns. Here, we use a natural experiment of a 2008 wildfire burning through a landscape with known 19th century fire severity patterns to test the hypothesis that fire severity patterns in a 2008 wildfire were similar to those in the late 19th century. Pre and post-fire measurements of plots and geospatial layers of vegetation type, terrain, fire weather, and daily fire extent and severity were used to identify spatial patterns and controls on fire severity in 2008. Tree mortality and bark char in plots were lowest on lower slopes, highest on upper slopes, and intermediate on middle slopes, and higher on the northeast than southwest facing slopes. There was a strong correspondence between 19th century and 2008 fire severity classes by slope position and slope aspect. Vegetation type, elevation, slope aspect, slope position, and to a lesser extent fire weather were the variables controlling fire severity. This indicates a combined influence of topography, vegetation, and fire weather on fire severity patterns. These findings highlight the role of the topography and disturbance legacies in shaping contemporary patterns of fire severity. Spatial persistence of severity patterns suggests wildfires burning under moderate conditions even during a period of climate warming can help reduce the fire deficit in fuel-rich forests and promote forest resilience in fire prone landscapes.

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