Fire Ecology and Monitoring
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 dependence refers to plants and animals that are adapted to and rely on the effects of fire to survive. For example, lodgepole pine and giant sequoia trees use fire to help open their “serotinous” or sealed cones, to remove litter and duff from the ground to allow seeds to germinate, and to burn open the canopy, affording seedlings the sunlight they need to grow big and tall. Restoration of the natural fire cycles through prescribed burning and other managed fires is perhaps the most important action that can be taken to restore and protect the natural abundance, diversity, and distribution of flora and fauna in the park.
Under natural conditions, fire maintains diversity in vegetation, which provides an abundance of ecological niches for wildlife. For example, fires under natural conditions most often burn in a mosaic of intensities, ranging from areas of light burning of surface fuels to areas of stand-replacing fires that create gaps in the forest canopy, while adjacent areas are untouched. Under such a pattern, a wide range of wildlife species, which are adapted to take advantage of different habitat conditions created by a fire, can exist in a relatively small area.
Additionally, American Indians have had a dramatic impact on the landscape for thousands of years. You can see evidence of their land management practices in the meadows, the woodlands, and the forests of the Park. American Indians conducted controlled burns to stimulate plant growth for forage for wildlife, for basketry materials, and for fire-proofing their communities. Experts estimate that millions of acres of land burned in California before European Americans settled the state and employed suppression tactics to fires Our landscape is largely the result of these early land managers and we continue their work through prescribed burns and managing wildfires for natural resource benefits.
By studying fire history, fire ecologists today are able to build a picture of how natural fire acted historically on the landscape and apply that knowledge to prescribed fire plans and wildland fire management strategies.
The fire suppression era in Yosemite (approximately 1850 to 1970) dramatically changed the fire regime in the lower mixed conifer vegetation type, leaving too many trees, more fire-intolerant trees, and few gaps in the canopy. By removing fires for 100 years from this ecosystem we changed the aspects of the fire regime and thus changed the forest. Yosemite is currently working to return the lower mixed conifer community to its historic fire regime using prescribed fires and other management techniques. Fire regimes and vegetation communities vary with elevation. There are eight major vegetation communities in Yosemite, all of which have a different fire regime and have adapted to fires that have occurred over the last ten thousand years. For example, the lower mixed conifer vegetation community burned frequently and at low intensity for thousands of years. Sequoia groves burned frequently as well. However, the higher elevation forests of red fir and lodgepole pine burned less frequently and probably only during periods of drought. Because more time occurred between these burns, fuel—including underbrush, and dead and downed wood—had more time to accumulate, resulting in fires that burned hotter and with more intensity.
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.