Restoring natural fire regimes is an important component of maintaining park ecosystems for the enjoyment of future generations. A fire regime is defined according to fire characteristics such as intensity, frequency, severity, season, extent, duration, behavior, spatial distribution, and type of fire. Most of the vegetation communities in the parks have adapted to fires that have occurred for at least the last several thousand years. While the habitat and life cycles of many plants and animals rely on the rejuvenating process of fire, the size, frequency, and timing of these natural fires varies depending on such factors as vegetation community, topography, and climate.
A program to better understand fire regimes prior to European settlement and to monitor the effects of fire's reintroduction is designed to provide the best available information to park managers in their efforts to restore and perpetuate fire as a process. This program includes fire history research to better refine our knowledge of where, when, and how fires burned in the past so that managers can better emulate historic fire regimes where possible. This is coupled with a long-term fire effects program to study changes in fuel load, vegetation structure, and composition resulting from prescribed fire, which is critical for assessing the progress of the parks' effort to reintroduce fire.
Fire managers use three tools to restore the benefits of this natural process: prescribed fire, mechanical thinning, and wildland fire. While visiting Yosemite, you may see evidence of any of these practices.
Prescribed fires are ignited by qualified park fire staff under certain pre-determined conditions. These fires are carefully managed to achieve such goals as public safety by protecting developed areas, and ecosystem restoration by clearing unsafe accumulation of dead and down wood.
Mechanical thinning requires the use of chainsaws to cut smaller trees and brush, as well as chippers if needed onsite. You may see piles of cut material. There may also be park vehicles and trucks near the site to haul away any excess material.
Wildland fires caused by lightning may be allowed to burn in certain park wilderness areas under specific conditions, and with close surveillance by park fire staff. These fires may be managed and allowed to burn to fulfill their natural role as an agent for the ecosystem. Where it is not prudent to allowfires to burn, park fire staff will suppress them.
During the 2003 fire season, Yosemite Fire Management staff plans 7,519 acres of prescribed burns and 988 acres of mechanical thinning. During your visit, you may notice signs along roadways indicating that a managed fire is in progress. Fires in Yosemite National Park;natural or prescribed;may result in smoky conditions and reduced visibility. Please observe all warning signs posted in fire areas. Visitors with respiratory problems may need to use caution when exerting themselves in smoky areas.