People usually do not perceive a forest or shrubland that has just been burned as natural or welcome. But fire is a part of the natural world, just like the wind, rain, snow, and other natural forces. Fire occurs in nearly all terrestrial ecosystems (large geographic areas with a community of organisms that are linked by energy and nutrient flows and that interact with each other and with the physical environment). In some ecosystems, wildland fire is one of the major factors in maintaining the community structure and composition, and assuring species survival.
Ecology is the study of relationships among living (biotic) and non-living (abiotic) elements of the environment. Fire ecology is a branch of ecology that studies the relationship of fire with living organisms and their environment.
© 2001 Karen Wattenmaker Chaparral fire races up a mountain-side*
Crown fire burns Ponderosa pines
Four concepts provide the basis for fire ecology:
1) Fire Dependence: This concept applies to natural communities that are adapted to and rely on the effects of fire to make the environment more hospitable for that community’s plants and animals.
2) Fire History: This concept describes how often fires occur in a geographical area. Fire scars, or a layer of charcoal remaining on a living tree as it adds layers or rings of wood annually, provide a record that can be used to determine when in history a fire occurred.
Repeated surface fires cause a sequence of overlapping
wounds. The heat-killed wood tissues extend into the
annual rings,which can be dated to the calendar year.*
3) Fire Regime: A fire regime is a generalized way of integrating or describing various fire characteristics (such as fire intensity, severity, and frequency) and the vegetative community where the fire occurs.
4) Fire Adaptation: This concept applies to species of plants that have evolved with special traits that allow them to successfully survive, and even require, fire. For example, cones that remain closed until opened by the heat of a fire (serotiny), fire resistant bark, fire resistant foliage, or rapid growth and development enable various kinds of plants to survive and thrive in a fire-prone environment.
Fire Effects on Vegetation
One major effect of fire is a change in soil nutrients. Fires release nutrients (such as nitrogen, phosphorus, and carbon) from woody vegetation back into the soil in the form of mineral-rich ash, which makes them readily available for new plant growth.
Smoke and ash fill the air in East San Diego County Photo by Marcello Mastrocola
Plant regeneration begins almost immediately following a fire. At any given location, different types of vegetation develop over time in orderly stages called succession. The natural recovery of the vegetation following wildfire depends on plant species that either survive fire in place (regrowth through resprouting) or are capable of colonizing the immediate post-fire site from seed. As a result, the severity of the fire directly influences the types of species and number of plants that survive and recover afterwards. Each successive stage is also determined by climate, soil conditions, geography (location) and available sunlight.
Although fire may destroy individual trees and understory plants, that is, plants growing beneath larger ones, the species themselves are well adapted to survive. In many cases, this is accomplished through a high regeneration capacity. For example, mature Coulter pine trees, which grow at higher altitudes in the mountains East of San Diego, are somewhat fire resistant but may be killed by a very intense fire. However, the serotinous cones that remain closed while on the tree are opened by the heat of a fire. After a fire burns through a mixed conifer forest, a multitude of seeds are dispersed from the open cones to the forest floor where they germinate and grow. The resprouting of shrubs and grasses from underground stems, stumps, or roots is another fire adaptation. Species like chamise, manzanita, and both coast and canyon live oak commonly recover in this manner.
Coulter pine cones
Fire Effects on Wildlife
The effects of fire on a habitat, which includes an animal's surroundings or home, are generally more significant than immediate effects on the animals themselves. Most wildlife species have proved very adept at avoiding being burned in a fire either by moving out of the area or retreating below ground. In fact, many wildlife species thrive on the occurrence of fire. The grasses, seedlings, and resprouting shrubs and trees that cover burned areas provide an ideal environment for many small seed-eating mammals and birds, such as voles and sparrows. This abundance of small prey attracts larger predators like foxes, hawks, and weasels. Burned trees provide sites for birds like flickers, kestrels, and chickadees which nest in holes in dead, standing trees, while woodpeckers thrive on the insects that inhabit fire-killed trees. As post-fire recovery of the vegetation proceeds, the types of animal species found in the burned area changes as the habitat changes. Some species found in a particular area prior to a fire may not return until the habitat recovers to its pre-fire state.
Photo by Marcello Mastrocola
Smoldering stump on Highway 79 in Cuyamaca Rancho State Park after the Cedar Fire
Fire ecology is an exciting subject that incorporates ideas from the physical, chemical and biological sciences, plus mathematics. The more students learn about this topic, the greater our potential to understand and thus more effectively manage wildland fires.
Sources: Adpated from
Western Fire Ecology Center. (2005). Introduction to fire ecology. Retrieved January18, 2005 from http://www.fire-ecology.org/education/doc1.htm
National Interagency Fire Center. (2005). Communicator's Guide: Wildland fire. Retrieved January 18, 2005 from http://www.nifc.gov/preved/comm_guide/wildfire/index2.html
*California Department of Forestry and Fire Protection (2004). California fire siege 2003: The story. Retrieved January 18, 2005 from http://www.fire.ca.gov/php/fire_er_2003siege-video.php
*Grahame, J.D., & Sisk, T.D.(Eds.). (2002). Canyons, cultures and environmental change: An introduction to the land-use history of the Colorado Plateau. Retrieved March 16, 2005 from http://www.cpluhna.nau.edu/Tools/fire_scars.htm
Mastrocola, M. (2003). Selected photographs. San Diego, CA: Author.
Wattenmaker, K. (2001). Photo of Clear Ceek, Salmon, Idaho. Retrieved Jnauary 10, 2005 from http://firepix.blm.gov/nifc/main.jsp?screenwidth=1152&ip2=0/