Altered Fire Regimes
Sierra Nevada forests have evolved with and are dependent on a recurring frequency of fire. A fire regime of a given plant community refers to the general characteristics of a fire typically found in that community under normal conditions. Attributes such as fire frequency, intensity, magnitude, and seasonality are used to define the fire regime. Vegetation type, elevation, topography, and climate also influence the fire regime by providing physical parameters within which a fire will occur.
The forests of the Sierra Nevada are greatly varied and therefore host a wide variety of fire regimes. The presence of fire in a these plant communities has a direct and significant effect on the ecological processes and wildlife present. All plant communities and the species within them have evolved dependent on the historic fire regime in that community. Any alteration of that fire regime over time will have a direct impact on the health of the vegetative community and on the long-term survival of certain plant species. While the fire regime stays out of line with its historical state, vegetative communities throughout the Sierra will be modified, thus impacting all of the species which depend on them for survival.
Fire regimes in the Sierra Nevada have been significantly altered due to a well intentioned but misguided campaign by the U.S. Forest Service to suppress fires within our national forests. We can remember the “Smokey the Bear” messages which called on all of us to prevent forest fires. This policy of suppression effectively eliminated fire from our forests and changed the fire regime. Plant communities once dependent on a frequent low-to-moderate-intensity fire, such as ponderosa pine-dominated mixed conifer forests, were now no longer being exposed to these essential fire events. Wildfire is such an influential ecological element that the regeneration of some plant communities and the survival of many plant species require fire. Well coupled with the selective logging of large trees, intense grazing operations, and road building activities, fire suppression over the past century has completely reshaped forest structure and altered ecological systems throughout the Sierra Nevada.
Before this active fire suppression program, forests in the Sierra Nevada were often represented by a landscape of large, well-spaced trees, with well maintained levels of brush and ladder fuels. Today, many of our forests are over-grown with species that would have otherwise been regulated by fire. In such an environment, a single lightning strike can lead to a catastrophic wildfire as it consumes the excess fuel which has accumulated over the years. Fire ecologists generally agree that in order to restore native plant communities, fire needs to be returned to forests at intervals consistent with historical fire regimes. Unfortunately, a century of fire suppression has led to a sharp rise in the volume of fuel in our forests and in order to reestablish the historical fire regime, much of the affected acreage must be managed in some way.
The use of prescribed fire in many of these impacted forest communities has proven to be an excellent method and has not only reduced the high fuel in the areas where it has been utilized, but its use also has important ecological benefits by returning fire to the forest. Yet, while prescribed fire is widely considered a necessary tool to restore ecosystems and reduce the risk of catastrophic wildfire, and its use has continued to increase, it is currently applied to very few forested acres of the Sierra Nevada.