1. Abstract This paper examines the present-day climate and vegetation patterns in the Willamette Valley, and forms part of a larger theme session entitled “Earth Science in Context: Land use and Watershed Function in the Willamette Basin”. The Willamette Valley climate zone encompasses a 200-km-long lowland that lies between the Coast and Cascade ranges. This region is characterized by generally cool, wet winters and warm, dry summers. The Mediterranean climate pattern results in a unique assemblage of vegetation, including the dominance of coniferous forests. The focus of this poster is on elevation-controlled changes in vegetation throughout parts of the Willamette Valley, as a function of local climate variation. Introduction The past and present regional climate and vegetation section of this theme session is intended to bring a better understanding to the setting of the watershed of the Willamette Valley and the physiographic framework. The Willamette Valley has the most varied vegetation pattern in Oregon along with the greater part of the state’s population. The valley is made up of alluvial flats broken up by low rolling hills. Although the largest contributing factor of vegetation difference is elevation change, the valley is fairly flat, only rising from 50 meters in Salem to 129 meters in Eugene. This leads to the sluggish meandering of the Willamette River. As is normal in the Pacific Northwest, the amount of precipitation also falls as you move south while the temperature rises. Methods In trying to understand the setting of the Willamette Valley we can look at the factors that influence the mosaic of vegetation. The valley has a long growing season. It lasts 150-180 in the lower areas of the internal valleys and 110-130 in and above the foothills. Another characteristic of the PNW is the dominantly coniferous forests. Evergreens are usually the pioneer or seral species and grow into a hardwood dominated forest, but here in the wet, mild climate it is the opposite. It is thought to stem from the historical climate events combined with our present climate that is very favourable to evergreen. The two climactic factors of today are the high precipitation and mild winters. Methods (cont.) The Willamette Valley itself is relatively warm and dry which is not as favourable for conifers. Even in the time of the first settlers the valley was not covered in forest and so was one of the first places settled. Because of this the valley has been experienced extensive humane influence. Cities, farms, and other development have altered the valley. Now, even the natural areas of the valley have a trace of human impact, which includes the affects of pre-settlement Native Americans and their use of wildfires. Discussion and Conclusions The climate and vegetation of today’s Willamette Valley has come together to create a unique mosaic. The Pacific Northwest has a distinctive climate that has shaped the valley and the human impacts of settlers and pre-settler Indians have impacted the region as much as the climate has. Changes in elevation and precipitation have affected the succession of the forests in a way not common to other Mediterranean zones, leading to the dominance of coniferous species. The forests have high stand productivity and biomass accumulations that have benefitted the lumber companies which in turn have their own affects on the valley. The valley’s diverse agricultural area and long growing season also lends itself to a favourable agricultural region The combination makes the Willamette Valley and Oregon a favourable place to settle. By understanding the region we gain a better grasp on the land where we build and live. Figure 3. A map of Oregon’s annual precipitation. (Oregon Climate Service, 2005). References Cited Franklin J.F.; Dyrness C.T., 1988, Natural vegetation of Oregon and Washington. Reprinted with new bibliographic supplement, Oregon State University Press, 452p. Oregon State University, 1999, Taylor, G., 2005, Special Report: Climate of Oregon, Special Climate Analysis Service, Oregon State University, Taylor, G.H., and Hannan, C., 1999, The Climate of Oregon: from rain forest to desert: Oregon State University Press, Corvallis, 45-56. Present-day Climate and Vegetation of the Willamette Valley Prepared by: Laura Stallard ES473 Environmental Geology Results Figure 1. Mean Temperatures in the Willamette Valley (Taylor and Hannan, 1999). Figure 2. Map of the Willamette Valley (Oregon State University,1999). All of the factors above have created the present day vegetation patterns in the valley. Today there are five different categories of vegetation: Quercus woodlands. Coniferous forests: Large areas are clustered on the foothills. Grasslands: Before settlement and now grassland covers a wide area with perennial, annual, and forbs grasses. Sclerophyllous shrub communities: More common in the southern valleys. Riparian forests: Dominated by hardwoods in places of poor drainage and annual flooding. Today 82% of Western Washington and Oregon is still classed as forest land. The Willamette Valley also splits the Tsuga heterophylla zone which occurs in the Coast Ranges and the Western and High Cascades. It is the most extensive of the zones. SummerWinter HighLow 80's~40 LowLow 50'sLow 30's Mean Temperature: