Fire Ecology Volume 12, Number 1
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Since 1989 Eco-LinkLinking Social, Economic, and Ecological Issues Fire Ecology Volume 12, Number 1 When it comes to thinking about fire in the forest, generations of Americans have grown up heeding the wisdom of Smokey Bear.For the increasingly urban population of North America that means excluding fire from the forest ecosystem at all costs. This mindset, reflected in US wildfire policy has resulted in over-crowded, unhealthy forests that, ironically, are at high risk for catastrophic fires. Of all of the natural forces that have shaped forest ecosystems over the millennia, fire has had the most impact. Fire has helped to control competitive species and prevented overstocking. And unlike other forces like wind and weather, fire can be harnessed as a management tool. Native peoples saw fire as an ally and were proactive in its use. They used it to clear land for settlements, travel, and agriculture. Fire, both natural and man-made, has been such an omnipresent force in the forest that many modern forest ecosystems are fire dependent and need fire to maintain a healthy condition. An overcrowded, unhealthy forest. Fuel treatment including prescribed fire can thin tree stands As a result of proper fire-treatment, forest are more and eliminate overgrown vegetation on the forest floor. open and healthy. Fire can be friend or foe depending on whether it is under control or out of control. As a natural phenomenon, it is linked to the dynamics of many plant communities and animal populations. Many species of trees can withstand and thrive from the periodic low intensity burns that have historically affected them. In addition, fire helps open cones to release seeds on some species and helps recycle nutrients into the soil. The application of regular fires is a critical process for forest health. But the forests does suffer from larger intensity fires and as the boundary between wildlands and civilization draws ever closer, wildland fires poses a threat to lives, property, and resources as well as the forest itself. Balancing concerns about the (perceived and real) threat of fire with its usefulness as a forest management tool is the dilemma facing policy makers and forest managers in this new century. The history of forest policy reflects a changing attitude and awareness of what fire is and what role it plays in the land. Understanding the benefits and the dangers of fire, the possible uses and avoidable misuses, is an important step towards maintaining a sustainable future. Photos by (left to right): Roy Lawson/Temperate Forest Foundation Archive, Bryan Day, Karen Wattenmaker/Courtesy of NIFC/BLM Eco-Link is a quarterly publication of the Temperate Forest Foundation © 2002 Temperate Forest Foundation About Fire and Fuels The word fire is from the Greek pyra meaning glowing embers. Fire is the heat and light that comes from burning substances. It is the visual indicator of the chemical process called combustion where some sort of fuel–such as the cellulose in wood–is combined with heat and oxygen to release energy. Sustained combustion from an ignition source requires a constant source of these three elements, often referred to as the fire triangle: fuel, heat and oxygen. Fire will be extinguished if any of the three of these components is depleted or missing. Fire Triangle How large a fire can become is determined largely by the fire behavior triangle: weather, topography, and fuels. Fire is more prevalent in summer months where hot, dry conditions are more conducive to starting and sustaining blazes. In the same way fire to travels uphill more easily due to convection. But Weather O Topography x t y most important in understanding fire behavior is understanding fuels. a g e e H n How a wildfire burns depends largely on the available fuels. In the wild, fire is typically spread by fine Fuel fuels (pine needles, leaves, grass, etc.) both on the surface and in the tree crowns. These are known as one Fuels hour time lag fuels, because they dry out (lose two-thirds of their moisture content) in about an hour. Small fuels, known as 10 hour time lag fuels, are woody twigs and branches, up to one inch in diameter; these fuels also help spread wildfires because they ignite and burn quickly. Larger fuels–particularly the 1000-hour time lag fuels (more than three inches in diameter)–may contribute to the intensity and thus to the damage fires cause, but contribute little to the rate of spread, because they are slow to ignite Types of Wildfires Not all fires in the wild are catastrophic. Low intensity fires can be helpful in maintaining some fire- adapted ecosystems. Indeed, fire is sometimes necessary, in some serotinous species, to release seeds for reproduction. Many species of mature trees are able to withstand all but the most intense blazes. But years of fire suppression and logging practices in public forests have resulted in high fuel loading which allows fires to burn hotter and climb into the tree canopies or crowns. These conflagrations can clear Surface fire burning off forest undergrowth out stands of trees. The three primary classes of wild-land fires are surface, crown, and ground.These classifications depend on the types of fuels involved and the fire’s intensity. Surface fires typically burn rapidly at a low intensity and consume light fuels while presenting little danger to mature trees and root systems. Crown fires generally result from ground fires and occur in the upper sections of trees, which can cause embers and branches to fall and spread the fire. Ground fires are the most infrequent type of fire and are very intense blazes that destroy all vegetation and Crown fire consuming large trees organic manner, leaving only bare earth. These largest fires actually create their own winds and weather, increasing the flow of oxygen and “feeding” the fire. Older trees, which can survive ground-level fires, don’t live through flames that climb up small trees like ladders to engulf the treetops. As fire is carried into the crowns of the trees it more easily can travel to adjacent trees–other fuel sources–further compounding the problem. Ignition Sources In the wild, there are two main catalysts for fire–lightning strikes or humans.According to the US Fire Administration, humans cause 88% of wildland fires while lightning is responsible for 12%. (1988-97 average–Based on data from the National Interagency Fire Center) Conversely, lightning-caused fires are responsible for 52% of the acreage burned as opposed to the 48% that human-caused fires burn. Fire Control Fire control involves removing one of the elements required to sustain fire–such as removing the continuous fuel supply for the fire by creating a fire line dug down to mineral soil or suppressing the heat or oxygen with water or chemicals. Fire is a force that can easily grow beyond our ability to control. At very high fuel loadings, fire behavior overwhelms even the best fire suppression efforts. Under extreme conditions, control of fire becomes dependent on relief in weather or a break in fuels. Eco-Link Fire Ecology (2002) 2 Fire and Forest Health Fire is recognized, by the US Government, as a critical process affecting forest health. Forest health is defined by the US Forest Service as; a condition wherein a forest has the capacity across the landscape for renewal, for recovery from a wide range of disturbances, and for retention of its ecological resiliency while meeting current and future needs of people for desired levels of values, uses, products, and services. Many forests have become fire dependent, requiring regular fire regimes to maintain their health. The maintenance of regular burning regimes helps prevent surface fuel buildup and an over-accumulation of small trees and brush that makes forests more susceptible to severe wildland fires, insect infestations, and disease outbreaks. Healthy forests are vitally important as animal habitat, as watersheds, and for resource production. Fire affects forest health issues such as fuel loading, wildlife impact, and watershed impact. Benefits of Light Burning In addition to maintaining open forests, fire serves fuel reduction, site preparation for seeding or planting, enhancement of wildlife habitat, control of undesired vegetation, range forage improvement, forest pathogen control, improved access, improved appearance, biotic community restoration and maintenance, enhancement of rare or endangered species. Burn cleared forest Fire Regimes and Fuel Loading Forest fire regimes have been altered by exclusion efforts, combined with other land-use practices, so that today’s fires tend to be larger and more severe than those of past centuries.As described earlier, many established trees are capable of surviving smaller, surface fires. “Open ponderosa pine, larch, and Douglas-fir forests at lower elevations in the West burn naturally every 5 to 30 years,” according to Robert W. Mutch writing for the Journal of Forestry, “maintaining rather open, fuel-free stands with few fir trees. But in more recent times managers have harvested the larch and pine overstory extensively while excluding fire. In the absence of fire, stand composition has shifted toward an unnaturally dense understory of Douglas-fir, grand fir, white fir, or incense cedar. Spruce budworm, Douglas-fir bark beetles, other destructive pests, and forest diseases have enjoyed a steady diet of stressed fir trees, leading to mortality, fuel build ups, and high-intensity wildfires.” Wildlife Impacts Post-burn regrowth Fire effects on wildlife are complex because they are often indirect, affecting habit more than individuals. Fire is beneficial to some species and detrimental to others. Fire benefits animals by clearing out the forest floor–old, woody growth gets burned off to be replaced by new succulent shoots sought by elk.