Item 3: PH on Ordinance Prescribed Wetland Management Burning

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USE OF PRESCRIBED FIRE IN WILLAMETIE VALLEY NATIVE PRAIRIES Edward R. Alverson The Nature Conservancy The main drawback of prescribed burns from the point of the general public is the smoke that is generated. While a prescribed burn may resemble a grass field burn, the amount of smoke produced by a prescribed burn in a native prairie is much less than a burn of an equal area of grass seed field. This is because the amount of fuel present in a grass seed field is 2 to 4 times greater per unit area than in a native prairie. Prescribed burns in Eugene are only conducted when the prevailing wind blows the smoke away from the populated urban areas, and under atmospheric conditions that provide for the most efficient dispersal of smoke. Generally small burn units also mean that the actual length of time during which the burns occur is quite short. 4. Alternatives to Prescribed Burns A number of alternatives to prescribed burning have been proposed, but none appear to provide all of the ecological benefits of fire. Mowing can inhibit the growth of woody plants and maintain the open prairie aspect. Mowing also may improve habitat for some ofthe rare prairie species, if it is done at the proper time of year. For example, the Bradshaw's lomatium population in Amazon Park has greatly increased in size over the past ten years since the first mowing has been delayed until the plants have finished growth and the seeds have matured in some time in July. However, mowing large acreages can be expensive, and wet prairies typically have a very irregular surface with numerous divots, hummocks, and ant mounds that make equipment operation difficult. Mowing may promote the growth of invasive non-native grasses such as tall fescue (Festuca arundinacea) Mowing also does not provide the nutrient cycling benefits or microhabitats suitable for seedling germination that fire provides. Manual labor can be used to remove woody plants that have invaded prairie habitats. In fact, at Willow Creek we have determined that manual removal is necessary to achieve our management goals because the ash and pear trees are too well established to be removed by fires occurring on a 2 to 5 year interval. Removal of woody plants also reduces the amount of fuel that the fire could consume, and reduces the smoke that is produced by prescribed fire. However, once the woody plants are removed, fire plays a useful role by killing back any seedlings or stump sprouts that may emerge. Using heavy equipment to remove woody plants is not a feasible option in native prairie remnants, because the soil disturbance would damage existing vegetation and likely allow invasive non-native species to increase. Using manual labor to remove woody vegetation causes little damage to the existing herbaceous cover, but is also expensive. It may be possible to use tractor-mounted propane torches to achieve some ofthe ecological benefits of prescribed burns in sites that are especially smoke-sensitive. However, the same problems with negotiating the divots, hummocks, and ant mounds mentioned above under mowing are pertinent here. Some of these alternative techniques have been compared with prescribed burning on small test plots at the BLM property between Danebo and Beltline in West Eugene. Small test plots were burned in 1994, 1996, and 1998. Although this was a small study, the researchers found that burning reduced 5