Item 3: PH on Ordinance Prescribed Wetland Management Burning

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ATTACHMENTE USE OF PRESCRIBED FIRE IN WILLAMETTE VALLEY NATIVE PRAIRIES Edward R. Alverson The Nature Conservancy March 2006 Prescribed fire has been used as a management tool on a number of natural areas in the Willamette Valley, and scientists continue to view fire as an important management practice for meeting natural area management goals. Like any management tool, fire has potential hazards, as well as the benefits it provides. The purpose ofthis paper is to provide the background historical and ecological information necessary to understand why prescribed fire is considered to be so essential to natural area management in the Willamette Valley. 1. Natural History and Role of Fire in the Willamette Valley The first explorers and settlers who arrived in the Willamette Valley in the early 1800's described the Willamette Valley as supporting extensive areas of prairie and oak savanna. Land surveys conducted by the General Land Office ofthe US Government in the 1850's documented that about 1 million acres of the Willamette Valley were prairie lands at that time. These native prairie habitats have been greatly reduced in extent due to agriculture, grazing of domestic livestock, residential and urban development, and expansion offorest vegetation into former prairies. Only small remnants of high quality native prairie are known to currently exist in the Willamette Valley at present. The exact number of remaining acres has not been documented, but the reduction from the original extent has been estimated to be close to 99%. The exact details of how the prairies originally became established are uncertain. The prairies may have become established during a time when the climate was warmer and drier than today (Hansen 1942). At present, the climate of the Willamette Valley is sufficiently cool and moist to support forest vegetation on most sites in the absence of disturbance, but grassland or savanna may have been the "climax" vegetation at an earlier time when the climate was warmer and drier than today. However, there is some evidence that the extensive prairies were maintained, if not actually created, by fires set by Native Americans. A study documenting pollen deposits in the Willamette Valley since the end ofthe ice age has shown a positive correlation between increases in grass pollen and increases in charcoal contained in the sediments at certain times in the past (Pearl et aI., 1999). This suggests the possibility that prairies may have been created or maintained by human-set fires, since the incidence of lightning-caused fires in the Willamette Valley is generally low. More studies are needed to provide greater understanding of how prairies and savannas came to dominate the Willamette Valley in prehistoric times, but many researchers today believe that fire played a significant role. The Kalapuya Indians had abundant motivation to use fire in the landscape (Boyd, 1999). Because of the falls on the Willamette at Oregon City, the Willamette was not a major salmon stream, and the Kalapuya did not utilize salmon to the extent that tribes along the Columbia River did. Instead, the