Uncharacteristic wildfires in the frequent-fire forests of the southwestern United States have increased in frequency and severity over the past few decades, driven primarily by land-use patterns and exacerbated by drier conditions and longer fire seasons. Research suggests that forest restoration can reduce the potential of uncharacteristic fires and reestablish resilient forest structure and function. However, decreasing funding and increasing extents of at-risk forests in the Southwest calls for prioritization of restoration treatments. Improving our understanding of the spatial distribution of fuels and the drivers of fuel accumulation can provide critical information for land managers who design and implement restoration treatments. Additionally, simulation of fire behavior and severity can provide insights into the potential impacts of fire on landscape pattern and resilience. In this study, we analyzed priority watersheds in ponderosa pine and dry mixed-conifer forests of northern Arizona to meet the following objectives: 1) determine the drivers and spatial distribution of hazardous fuel accumulation across the watersheds, and 2) characterize the dominant landscape patterns following simulated fire. Spatial distributions of hazardous fuel accumulation were derived from discrete return airborne lidar data, and drivers of fuel accumulation were determined using random forest modeling and chi-square tests for independence. We used the lidR package in R to produce datasets that initiated conditions in FlamMap, which was used to simulate fire behavior. Resulting landscape metrics of crown fire patches were quantified using the landscapemetrics package.
Results/Conclusions
Results indicate a heterogeneous distribution of fuels across the landscape with higher concentrations of hazardous fuels around Blue Ridge Reservoir and in major ravines. Slope was the primary driver of hazardous fuel accumulation of the four topographic drivers assessed. Fire simulation outputs indicated that crown fire patches increased in extent, size, and density as fire weather became more extreme. Results from this study provide valuable information about the spatial distribution, potential scale of treatment, and drivers of hazardous fuels across priority watersheds in northern Arizona, which may guide land managers’ prioritization of restoration treatments. Quantification and mapping of crown fire patch metrics enhances our understanding of the potential impacts of wildfire on landscape pattern and subsequent forest resilience.