Variable Fire Severity Over Multiple Decades of Naturally Occurring Fire in a Sierra Nevada Mixed Conifer Forest

Of the many historical fire regime studies conducted throughout the Sierra Nevada only a few have been able to reconstruct the complex nature of non-lethal surface fire co-occurring with patches of stand-replacing fire. These few studies demonstrated that forest types found on mid- and upper-slope positions within the mixed conifer region, as well as forest types dominated by lodgepole pine (Pinus contorta var. murryana) historically experienced mixed severity fire, as indicated by the presence of both fire scars and even-aged cohorts. Due to an incomplete record of past forest structure and fire occurrence, such studies offer limited inference into spatial and temporal complexity of mixed severity fire. The multi-decadal record of satellite-derived fire severity maps in the Illilouette basin, Yosemite National Park, offers an ability to quantitatively characterize both the spatial and temporal complexity of mixed severity fire. Nineteen fires (\u3e 50ha.) have burned relatively freely in the Illilouette basin throughout the 35-year period of wildland fire use in Yosemite NP. In this paper we investigate differences among dominant forest types both in the proportion of area burned for 4 fire severity classes (unchanged, low, moderate, and high) and in the size distribution of high severity patches. Additionally, we investigate potential trends in fire severity by forest type for the 35-year period that could provide insight into the potential response of the fire regime to changing climatic conditions