Fire is an important part of Idaho’s different ecosystems. It serves as a cleansing agent for both forests and rangelands in many ways. Let’s look at two different Idaho ecosystems to see how fire changes the landscape, vegetation, and habitat for animals.
More than 60 percent of Idaho is covered in forests. Over time, the trees in these forests grow thick and close together, along with a lot of other vegetation both dead and alive. When this happens, the forest needs to clean itself in order to keep trees healthy and to provide new forage for wildlife. Wildfire helps forests to “clean themselves” by burning dead trees and other vegetation, along with the crowded plants and trees. Some wildfires burn all vegetation in a forest, but many of them burn in a “mosaic” pattern, which means that not all trees and vegetation burn in the fire. After a wildfire, new vegetation has room to grow. Trees can start to rejuvenate and new trees sprout because they have renewed access to sunlight. Tender grasses begin to grow, which attracts wildlife such as elk, deer, and antelope.
Good Fire and Bad Fire
Idaho has experienced several large, long lasting wildfires in recent years, which burned thousands of acres at a time. These fires are not always considered to be good for the forest, because they burn such a large amount of vegetation all at one time. Wildlife is often affected by these large burns. For example, sometimes animals such as deer, elk, rabbits, chipmunks, and other foraging creatures must find new areas to forage for food when thousands of acres have burned all at one time. It is safe to say that these large burns are “bad fires.”
Why do we have large fires? In many cases, large fires occur because of hot, dry temperatures and an intense build up of vegetation in the forest. When wildfires do not frequently burn in the forest, the vegetation accumulates and provides more fuel for larger fires. More fuel means more fire, which in turn creates large wildfires that are difficult to suppress and spread quickly.
Good fires occur when a fire ignites and burns slowly, burning mostly ground vegetation and a few trees. These fires help Idaho’s ecosystems by cleaning out dead and/or crowded vegetation, but the majority of large trees are left alive and able to repopulate the forest.
Some trees rely on wildfire to repopulate the forest. Many of these trees drop cones called “serotinous cones” from their branches. The seeds, sealed in the cone by resin, are stored for many years until they are exposed to intense heat that melts the resin covering the cone and allows the cone to open. The seeds are then able to germinate when conditions are optimum; in the ashes immediately after a forest fire. For example, Lodgepole pine trees are in many of Idaho’s forests, and many of them drop serotinous cones on the forest floor. These trees are considered to be “fire dependent” because they need fire in order to spread their seeds in the forest.
About 45% of Idaho is covered in rangeland. What are rangelands? They are areas that do not receive much rain and the native vegetation is made up of grasses, broad-leaved plants (forbs), and shrubs that can survive on little moisture, especially during the summer months. Rangeland can describe a prairie, plain, savanna, steppe, grassland, and many other ecosystems.
How much rangeland is there in the world? The many types of Rangeland together form about half of the earth’s land surface! Rangelands are very important to Idaho; they produce a wide variety of goods and services desired by society, including wildlife habitat, livestock forage, water, mineral resources, wood products, wildland recreation, open space, and natural beauty. It is very important to keep Idaho’s rangelands healthy.
Fire’s Role on Idaho’s Rangelands
Wildfire plays an important role in the health of Idaho’s rangelands, just like it does in Idaho’s forests. Juniper trees grow on Idaho’s rangelands. They are also fire dependent, just like conifer trees in Idaho’s forests. Without regular wildfires, juniper trees begin to grow in areas where sagebrush and grasses naturally grow. When this happens, juniper trees crowd out sagebrush and grasses, causing habitat loss for sagebrush-dependent birds such as sage grouse.
Fire and Noxious or Invasive Weeds
Wildfire can also bring opportunities for noxious weeds to grow on Idaho’s rangelands. Cheatgrass is an example of an Invasive weed; it is widely distributed throughout the western U.S. It is not native, meaning that it was introduced from another continent. The origins of cheatgrass are probably southwestern Asia; scientists think that grain brought from Europe in the late 1890’s had cheatgrass seeds in it, and they were then spread to Idaho’s rangelands. Because cheatgrass can grow in Idaho’s climate and soils, it has rapidly spread throughout Idaho’s rangelands.
After fires burn on Idaho’s rangelands, cheatgrass begins to grow before Idaho’s native plants because it sprouts early in the spring. When cheatgrass grows first, Idaho’s native plants do not have soil and water to grow. Cheatgrass is also very flammable and grows in a continuous bed of grass; whereas Idaho’s native grasses grow in clumps with separation between them. Because cheatgrass covers large areas, wildfire burns rapidly through it, creating larger, faster-moving wildfires that are difficult to control.
Why are Noxious or Invasive Weeds Bad?
Noxious or Invasive weeds compete with native plants for water and soil. They often push native plants out, which in turn takes food and shelter away from native animals. For example, cheatgrass has invaded Idaho’s rangelands, pushing out many of Idaho’s native rangelands plants such as sagebrush, important grasses, and forbs (flowering plants). Sage grouse depend on sagebrush for food and shelter, especially during mating season and winter months. When sagebrush diminishes, sage grouse begin to die off, along with other sagebrush-dependent animals. When this happens, the entire sagebrush-steppe ecosystem begins to break down.
The Fire Triangle
Fire must have three elements in order to burn; 1) Fuel 2) oxygen 3) heat. If you remove one of these elements, the fire will go out or diminish. For example, if you have a burning candle and you put a jar over the top of it, it eventually goes out. Why? Because you have removed the oxygen from the fire, and it cannot burn without it.
Firefighters extinguish fire by taking away one or two elements of the fire triangle. For example, when firefighters spray fire with water, it goes out because they have removed the heat element of the fire triangle. When firefighters dig fire line around a wildfire, the fire is extinguished once it reaches the fire line because firefighters have removed the fuel element from the fire triangle.
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Fire History is the occurrence and distribution of fires over time. Wildland fire scientists keep track of fires as they have burned in the past, so that they can learn from them. What do they learn? Scientists and firefighters can determine how hot fires have burned in the past, how large they were, where they burned, and how long ago they burned. They use historical records and journals, photographs, and vegetation age analysis. Vegetation age analysis involves looking at large trees and soil sediments. When large trees survive wildfire, they have fire scars on their trunks. Fire scars help scientists and firefighters determine when the fire burned, and can tell how intense the fire was by the size of the scar on the tree.
Firefighters can also use fire history to conduct prescribed burns. Click here to learn about prescribed burning in Idaho.