 * Critical Findings ASSESSMENT * Careless and Indiscriminate Fire Use
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ASSESSMENT
Fire represents both one of the greatest threats and one of the strongest allies in
efforts to protect and sustain human and natural resources in the Sierra Nevada.
Residents and visitors alike are well aware of the threats posed by summer wildfires.
A growing density of homes and other structures coupled with the increased amount and continuity
of fuels resulting from twentieth-century fire suppression have heightened concern
about threats to life and property, as well as the health and long-term sustainability of forests, watersheds, and other natural resources. Yet fire has been an integral
part of the Sierra Nevada for millennia, influencing the characteristics of ecosystems
and landscapes. Today, state, federal, and local agencies put enormous resources into efforts to reduce fire occurrence while at the same time advocating the need
to use fire to promote healthy ecosystems. The challenge we face is how to restore
some aspects of a more natural fire regime while at the same time minimizing the
threat wildfire poses to human and natural resources and values. The Nature and Ecological Role of Presettlement Fire
Fire has long been a natural component of Sierra Nevada ecosystems. For thousands
of years preceding Euro-American settlement, fires burned frequentlytypically multiple
times each centuryin most Sierran vegetation types. The hot, dry summer mediterranean
climate provided suitable weather conditions and dry fuels for burning. Lightning provided
a ready ignition source, supplemented by Native Americans, who used fire for a variety
of purposes. Fires could spread until weather conditions or fuels, or both, were no longer suitable.  Table 4.1 (Actual View 8K) Only one studyin high-elevation red fir found a median fire-return interval greater than thirty years. Using total area and our best understanding of the range of fire-return intervals for each of the major vegetation types, and a simplified assumption that, for each type, total area divided by fire-return interval equals area burned annually, we see that it was not uncommon for hundreds of thousands of acres to be burned in the Sierra Nevada in a given year. Yet fire frequency, intensity, and severity varied through time and across the landscape in response to variations in climate, number of lightning ignitions, topography, vegetation, and human cultural practices. Presettlement fire strongly influenced the structure, composition, and dynamics of most Sierra Nevada ecosystems. Many species and most communities show clear evidence of adaptation to recurrent fire, further demonstrating that fire has long been a regular and frequent occurrence. This is particularly true in the chaparral and mixed conifer communities, where many plant species take advantage of or depend on fire for their reproduction or as a means of competing with other biota. The variable nature of presettlement fire helped create diverse landscapes and variable forest conditions. In many areas frequent surface fires are thought to have minimized fuel accumulation, keeping understories relatively free of trees and other vegetation that could form fuel ladders to carry fire into the main canopy. The effects of frequent surface fires would largely explain the reports and photographs of those early observers who described Sierran forests as typically open and parklike. However, such descriptions must be tempered by other early observations emphasizing dense, impenetrable stands of brush and young trees. Several lines of evidence indicate that most presettlement fires were dominated by areas of low to moderate severity, with high-severity portions (fire sufficiently intense to kill most large trees) most often restricted to localized areas, often a fraction of an acre to several acresor occasionally several hundred acresin size. Predominately high-severity fires larger than a few thousand acres almost certainly occurred but were probably less common than they are today. This picture of presettlement fire is supported by our understanding of fuel dynamics as well as information derived from forest age structure analysis, written accounts of early fires, and observations of modern fires. Periodic fires performed a number of ecological functions. Fire damaged or killed some plants, setting the stage for regeneration and vegetation succession. Many plants evolved fire-adapted traits, such as thick bark, and fire-stimulated flowering, sprouting, seed release, and/or germination. Fire influenced many processes in the soil and forest floor, including the organisms therein, by consuming organic matter and by inducing thermal and chemical changes. And it affected the dynamics of biomass accumulation and nutrient cycling and generated vegetation mosaics at a variety of spatial scales. Native Americans adapted to this natural role of fire and controlled it to some extent for their own benefit. They are known to have used fire to clear brush from around their dwellings and to enhance habitat for game species. There is reason to believe that in local areas their activities added to the background lightning-induced fire frequency. 
 
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