Item 3: PH on Ordinance Prescribed Wetland Management Burning

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USE OF PRESCRIBED FIRE IN WILLAMETTE V ALLEY NATIVE PRAIRIES Edward R. Alverson The Nature Conservancy native prairie plants. We still have much to learn about fire effects in Willamette Valley prairies. Designing and conducting controlled experiments in field conditions is difficult, and it takes a number of years to obtain meaningful results. Data gathering is a complex and time consuming task, and we are just beginning to learn how to make experimental research more efficient. Clearly the monitoring data from prescribed burns will help us to improve our prairie management strategies as well as refine our priorities. 3. Benefits and Potential Drawbacks to Prescribed Burns Reviewing the landscape history of the Willamette Valley provides the perspective that fire has been an important component ofthe "natural" ecosystem for thousands of years, and monitoring data for recent prescribed burns supports the idea that many native prairie plants benefit from such fires. One ofthe reasons herbaceous prairie plants benefit from fire is because the fires that burn in these prairies are of low intensity and are of short duration. During a low intensity burn, the dried leaf litter is consumed, but the meristems (growing points) ofthe plants are left unharmed, protected in the crown of the plant or buried underground. The precise reasons for the benefits of fire are not fully understood, but a variety of mechanisms have been proposed. For some species, seeds may lie dormant in the soil until the heat from a fire breaks the seed coat and stimulates germination. The burning ofleaflitter that occurs during a fire releases nutrients and makes them available to plants when they otherwise would not be, providing a sort of fertilizer effect. When the leaf litter is burned, the bare soil that is left behind may be a better microenvironment for germination of seeds of native prairie plants, due to increased light and better contact with the soil. Other biological functions, such as microbial activity, may also be stimulated by fire. Of course, fires can have negative effects as well. Most animals are able to move out ofthe way of typical prairie fires, and we have observed only a minor amount of vertebrate wildlife mortality (small numbers of dead garter snakes) in previous prescribed burns in West Eugene. Invertebrates, especially those that are present in the leaf litter, may be more subject to mortality by prescribed burns, but their populations can usually persist if some areas of habitat are always left unburned. Because ofthis possibility, The Nature Conservancy burns more no more than 1/3 ofthe habitat of the endangered Fender's blue butterfly at Willow Creek in anyone year. Prescribed burns will always need to be treated with caution because of the potential for fire to spread beyond the burn unit. Safety is always the paramount consideration, and it is incumbent upon the burn boss to ensure that a prescribed burn is conducted under appropriate conditions. Fire managers use computer models to predict fire behavior given certain site conditions, and under specific weather conditions. These models are used to determine the appropriate range of temperatures, humidity, and wind speed under which a burn can be safely conducted. For each prescribed burn, a burn plan is prepared that states the conditions under which the prescribed burn can be safely carried out, and ifthose conditions are not met, the burn is postponed until a later date. The burn plan also specifies the crew and equipment needed, and the pattern by which ignition will occur. Safety is also bolstered by providing appropriate fire breaks that are mowed or plowed around the burn unit to help contain the fire within the desired area 4