Visitors to the Grizzly Giant in the Mariposa Grove of Giant Sequoias may also experience a prescribed fire. Fire helps encourage giant sequoia germination.

Wildland fire is a natural process--it is an agent of change, not of good or evil. Many disturbance forces, including fires, floods, and earthquakes promote changes and have an impact in an ecosystem.

"Fire ecology" is a branch of ecology that studies the origins of wildland fire and its relationship to the living and nonliving environment. There are three main areas of study within fire ecology: fire dependence, fire history, and fire regime.

Fire dependence
Beginning in the 1930s, researchers began to study the effects of fire in the wilderness. They believed that fire was essential to many plant and animal communities. Fire dependence refers to plants and animals that are adapted to and rely on the effects of fire to survive.

Fire history
Fire history is used to show how often fire occurs in a given area. Each year a tree adds a layer of cells, increasing the width of its trunk, and in the process, records fire history and climate. When a fire passes through a forest, trees may get scorched. A layer of charcoal remains on a living tree and, in time, is covered by a layer of new growth, creating fire scars. These fire scars provide a record that researchers can use to determine when a fire occurred in specific areas of a forest.

Fire regime
A "Fire regime" refers to the role fire plays in an ecosystem. It is defined according to fire characteristics such as intensity, frequency, severity, season, extent, duration, behavior, spatial distribution, and type of fire. There are eight major different vegetation communities in Yosemite, all of which have a different fire regime and have adapted to fires that have occurred for at least the last several thousand years. Though many species rely on fire for their regeneration, the timing and severity of fires varies greatly depending on weather and topography. The goal to better understand fire regimes is part of our fire management program.

Yosemite firefighter gathers weather data.

Fire Effects and Fire Monitoring

Yosemite's fire effects monitoring program studies the effects of fire and mechanical thinning on vegetation and fuels. Research plots are placed in prescribed burn, wildlife fire use, and mechanical treatment units prior to a fire or project. These plots are then studied after the burn or treatment to see what the ecological effects are. By monitoring the changes in vegetation during a prescribed burn, the prescription can be adjusted, if necessary, to achieve the desired results. By doing research such as this, we can learn if we are meeting fire management objectives.