Glossary
of terms

Beneficial fire refers to strategically planned use of fire on the landscape to reduce fuel loads and the risk of catastrophic wildfire, enhance forest health, and promote biodiversity.

A wildfire with unplanned, undesirable, and harmful effects to either forest ecosystems, human communities, or both. Harmful effects include loss of human life and heavy damage to homes, businesses, and critical infrastructure. In addition, a catastrophic wildfire often kills trees over a large area, far more than would burn in a good fire.

A catastrophic wildfire is not necessarily the same as a high severity wildfire. Some forest ecosystems depend on high severity fires to regenerate and maintain health. For example, high elevation lodgepole pine forests in the Rocky Mountains require high severity fires to open their serotinous cones—cones that are essentially glued shut with sticky resins and that can only open when exposed to high temperatures.

Carefully-managed, deliberate, beneficial fire designed by professionals and constrained to a specific area that provides land and public safety benefits including fuel reduction, weed control, and improvements in forest structure and composition. 

The practice used by Native Americans of applying fire to manage forests and other habitat. Cultural burning is used to provide benefits to the land and the people on it including for food, fiber, ceremony, and fuel management. Pre-settlement, cultural burns were used by many Native American tribes throughout the West and beyond.

This practice was largely outlawed by settlers and subsequent governments. Efforts over the last several years have resulted in the return of cultural burns to many western landscapes.

The western U.S. has many types of forests: Coastal rainforests, redwood forests, ponderosa pine forests, and others. These forest types are divided by scientists into broad categories based on moisture levels: dry, mesic (or moderate), and wet forests. Fire is present in every type of forest and can play a beneficial role in each.

Dry forests in the western U.S. have experienced extreme stress and have been the site of many of the high profile, catastrophic fires in recent years. Dry forests experience less precipitation than their mesic and wet cousins. Scientists define dry forests according to their historic fire return interval, which is essentially the average frequency of a wildfire over the last many centuries. This is heavily influenced by moisture levels. Dry western forests are those with a fire return interval of 40 years or less.

Map of dry western forests in the U.S.

A measure of the heat generated by a fire.

The typical pattern and severity of fire in a natural ecosystem over many centuries.Every forest deals with and adapts to fire. For example, dry ponderosa pine forests in Arizona historically had frequent, low-severity fires which regularly cleared understory vegetation. High elevation lodgepole pine forests in Wyoming experienced low frequency, high severity fires and have developed adaptations that help trees survive these fires.

During pre-settlement times, Native American fire managers contributed to fire regimes using cultural burns. Since then, fire regimes in dry western US forests have changed as human populations have increased. Dry forests that historically experienced high-frequency, low-severity fire regimes have suffered from fire suppression, resulting in overly dense, fuel-rich forests at risk of high intensity, high severity fire.

A measure of the effects of a fire on ecosystems, especially death of trees and other vegetation.

A high severity fire is not always a catastrophic fire. Some forests depend on high severity fire to stimulate a new generation of trees.

Any flammable material in forests that contributes to the intensity and spread of wildfire. Fine fuels include grasses, shrubs, needles, leaves, and other small dead material. When weather conditions are very dry, these fine fuels, in addition to standing trees in dense forests, are responsible for high fire intensity and fire spread.

Heavy fuels include larger woody material including branches, tree trunks, fallen and dead trees. Ladder fuels consist of small and medium sized trees that, at high intensity, can carry fire into the canopy of mature trees.

The careful application of a variety of practices by professional foresters to achieve desired outcomes. These practices include tree planting, prescribed fire, thinning, fire breaks, road building, wildlife management, invasive species removal, and more.

A resilient forest is capable of coping with a variety of stresses and disturbances including drought, insect attacks, disease, and wildfire. In the context of wildfire, a resilient forest is more likely to avoid catastrophic wildfire and drought and promote beneficial wildfire because tree density, fine fuels, and ladder fuels are all carefully managed.

Forest stand structure refers to the arrangement of trees and other vegetation across a forest area. Tree type, age, size, and spacing all help characterize forest stand structure, and are key factors influencing forest ecology, biodiversity, and overall forest health.

A forest management practice designed to reduce the density of trees in a forest. In dry western forests, it is often used to reduce fuels and make forests more like those that would have been present had good fire not been eliminated from the landscape by years of aggressive suppression. Forest thinning involves cutting carefully selected trees and removing those trees from the site. 

Ecologically based thinning in dry, frequent-fire forests promotes the conservation, growth, and regeneration of fire- and drought-tolerant species, diverse understories, and ultimately, restoration of the hydrological regimes that historically supported wet meadows and wetlands in forested landscapes.

Commercial thinning results in removal of logs that have market value. Those logs are hauled to mills to produce lumber and other products. In some parts of the west, logs that are too small to produce lumber are chipped and used as a feedstock for bioenergy.

Pre-commercial thinning generates small logs and other residue that has no market value. That residue is generally either chipped and spread on the treated forest or stacked in piles and burned at a later date (aka pile burning which is a type of controlled burn).

A forest with many old trees and a variety of other elements, including standing dead trees (aka “snags”), dead trees on the forest floor, and live trees of all ages. All of this complexity results in many types of habitat which in turn supports diverse wildlife.

Many old-growth forests were cleared during the 19th and 20th centuries for lumber. Most remaining old-growth forests are on public land but still face threats from catastrophic wildfire and insect outbreaks and in rare cases, from commercial timber harvest.

Any fire occurring in wildlands that is not planned by forest managers. This term excludes fires planned, set, and carefully controlled by land managers, for example prescribed burns and cultural burns.

Wildfire is a natural occurrence in all forest ecosystems. Wildfires contribute to the resilience and sustainability of forest ecosystems, showcasing nature’s intricate processes of renewal and growth.

Wildfire has different levels of fire intensity, or the strength of fire in a given place, and fire severity, or damage to vegetation, soil, and ecosystems.

Areas will often have their own natural fire regime, or the general pattern and behavior of fires that would naturally occur in a particular ecosystem over time.

Our nation’s vision for wildfire management as articulated in the National Cohesive Wildland Fire Management Strategy is this:

“To safely and effectively extinguish fire, when needed; use fire where allowable; manage our natural resources; and as a nation, live with wildland fire.”

Wildfire management requires managers to make careful decisions to sometimes use prescribed or cultural burns, sometimes allow wildfire to burn safely through forests that need fire; and, when appropriate, aggressively extinguish wildfires.

Making these difficult management decisions requires teams of highly trained fire fighting and forestry professionals using a wide variety of data and analysis with public safety as a paramount concern. It also requires an understanding that our forests need fire to stay healthy and that putting out all wildfires, at all times of the year, has allowed fuels to build up, making future fires worse.