Characterizing fire severity patterns in three wildland fire use incidents in the southern Sierra Nevada

Wildland fire use (WFU) is a tool that has been utilized by managers in the Forest Service since the 1970s to reintroduce fire as a natural ecosystem process. Today it is also applied to meet additional resource objectives including restoration and maintenance of ecosystems and fire hazard reduction through lessening the extent and severity of future fires. Few studies have characterized the spatial pattern of fire severity in either wildland or WFU fires. The objectives of this report are to: 1) use remotely sensed data and geospatial analysis to understand the influence of weather, topography, and fuels on fire severity, and 2) characterize fire severity patch dynamics for the Albanita-Hooker, Crag, and Clover WFU Fires in the southern Sierra Nevada. A regression tree analysis was completed with elevation, slope, aspect, time since last fire, burn frequency, wind speed, temperature, relative humidity, energy release component, and vegetation type as explanatory values to describe change in canopy cover derived from remotely sensed data. Change in canopy cover was most described by relative humidity, slope, and vegetation type for the Albanita-Hooker Fire; elevation, temperature, and energy release component for the Crag Fire; and relative humidity, temperature, and energy release component for the Clover Fire. The majority of the Albanita-Hooker and Crag Fires resulted in unchanged to low fire severity (70 % and 89 %, respectively). Mean (area-weighted) patch size for unburned to low severity was approximately 10 and 50 times the size of moderate and high severity patches for the Albanita-Hooker Fire, and about 100 times the size of both moderate and high severity patches in the Crag Fire. In contrast, a bimodal distribution of fire severity was seen in the Clover Fire, with 28 % unchanged to low severity and 62 % high severity, with the largest mean (area-weighted) patches occurring in the high severity category (6,889 ac). It is intended that the findings from this report will help managers understand which factors have the most influence on fire severity, and use this information to determine if WFU incidents will adequately return landscapes to a more historical fire regime. The Albanita-Hooker and Crag Fires primarily resulted in unchanged to low fire severity; the majority of the Clover Fire resulted in high severity Based on regression tree analysis topographic features and weather variables were the most influential factors determining canopy cover change for all three fires The Clover Fire reburned seven fires, with …