The variability of fire severity and forest landscape in Sequoia/Kings Canyon National Park.

Fire is a key natural process that shapes the structure and pattern of forests in the western United States; however, wildfires have been increasing in extent, frequency, and severity over the last several decades. This increasing fire intensity is mainly due to fire suppression practices; however, earlier spring snow melt and a longer fire season due to climate change also contribute to the increase of catastrophic fire. Fire suppression policies have effectively removed the process of natural fire and altered forest structure and fuel loads, such that many coniferous forests are now prone to uncharacteristically severe and extensive fire. Fire exclusion has led to increased surface fuels and tree density, and fuel continuity, thereby escalating fire hazards in many forests. In the Sierra Nevada of California, high-severity fires are well outside the historic range of variability for mid-elevation forests and are considered by many to be the greatest single threat to the integrity and sustainability of Sierra Nevada forests. Land managers are actively working to reduce the threat of catastrophic fires and to restore the ecological role of fire to these forest ecosystems. The purpose of this study is to gain understanding of the relationship between landscape and fire, and to compare the similarities and differences in landscape pattern and structure between an actively managed prescribed fire area and a remote natural fire area. Forest fire severity and variability are examined in relation to pre- and post-fire landscape pattern across 2 mixed conifer forests in Sequoia/Kings Canyon National Park to gain an understanding of the relationship between fire and management practices. Three fires were studied, 2 fires within the Giant Forest Grove, an actively managed fire area of Sequoia National Park and 1 fire within the Sugarloaf Creek basin, a remote natural fire area, of Kings Canyon National Park. Fire severity was calculated using remote sensing and field survey methods. Burn severity was more evenly distributed, categorically, in the natural fire area. Measures of species abundance and evenness were used to determine the influence that species composition and structure may have had on the variability of fire severity. The variability of burn severity was predominantly associated with the species that had the greatest level of importance within both study areas. In the natural fire area, stands with higher tree density burned with moderate- and high-severity fire. High severity areas also had smaller average tree sizes than low severity areas in both study areas. Large tree mortality and survival in relation to burn severity showed that large living trees throughout both study areas were mostly within low severity stands. Sapling dominance and distribution was associated with the frequency rate, percentage of mortality, and density of the established adult tree speices. The significance of this research rests on the fact that land managers are faced with multiple challenges in seeking ways to reduce the threat of catastrophic wildfires and in restoring fire to fire adapted ecosystems. Improved understanding of the outcomes from different management practices can help guide decision making on forest fire policy.