Ecology Vegetation & Wildlife
Wetland prairies of the Willamette Valley are seasonally flooded ecosystems dominated by herbaceous plants occurring on poorly drained lowland soils.
Poorly drained soils, combined with the relatively flat topography of the valley bottom, cause seasonal precipitation to collect, saturating the soil and often producing standing water, typically from November through April or May.
Willamette Valley wetland prairie vascular plant communities are comprised of a diversity of forbs, sedges, rushes, and grasses. This continued persistence of prairies over an extended period of time led to the establishment of a highly diverse assemblage of perennial and annual forbs and grasses. It is estimated that approximately 350 species, subspecies, and varieties of native plants are found within upland and wetland prairies in the lowland valleys of the Pacific Northwest.
The moist, mild winters and long summer droughts that define the climate of the Willamette Valley greatly influence the period of plant growth in wetland prairies, which occurs mainly in the winter and spring when soil moisture is high.
Native wet prairies in most of the valley are dominated by native Deschampsia cespitosa (Tufted hairgrass), Danthonia californica (California oatgrass), Hordeum brachyantherium (meadow barley), Juncus spp. (rushes), and Carex spp. (sedges) along with a varying diversity of perennial and annual forbs (Christy et al. 2011).
Camassia quamash and Camassia leichtlinii as well as woody species such as Rosa nutkana (nootka rose), Symphoricarpos albus (snowberry), Spiraea douglasii var. Menziesii (Menzies’ spiraea), and Fraxinus latifolia (Oregon ash) are often found as a component of a wetland prairie, with densities generally increasing in the absence of disturbances such as fire.
Today, almost all remaining wetland prairies in the valley are colonized to some extent by non-native plants, many of which are highly invasive. Among the most dominant and persistent of these non-native species are, Festuca arundinacea (tall fescue), Agrostis capillaris, A. stolonifera, (non-native bentgrasses), Holcus lanatus (velvet grass), Anthoxanthum odoratum (sweet vernal grass), Vulpia myuros (rattail fescue), Hypochaeris radicata (hairy cat’s ear), Mentha pulegium (pennyroyal), Alopecurus pratensis (meadow foxtail), and Phalaris arundinacea (reed canarygrass).
Many of these species are all capable of dominating a wetland prairie to the exclusion of almost all native species and in some cases will form large patches of monocultures. Other non-native species, such as Lolium multiflorum (annual ryegrass), Daucus carota (Queen Ann’s lace), Rumex crispus (curly dock), and Myosotis discolor (changing forget-me-not) persist in the habitat, but tend to be less invasive and coexist with native prairie species.
Knowledge of the wildlife communities that were present in pre-settlement Willamette Valley prairies is largely based on accounts of Native Americans, explorers, and early settlers. These accounts tended to be focused on game species, predators, and other large- to medium-size mammals of economic importance. It is estimated that 97 vertebrate species (amphibians, reptiles, birds and mammals) likely used Willamette Valley prairies for feeding and reproduction (Vesely et al. 2010).
At the time of Euro-American settlement of the valley in the mid-1800s, Roosevelt elk (Cervus canadensis roosevelti), Columbian white-tailed deer (Odocoileus virginianus leucurus), and black-tailed jackrabbit (lepus californicus) were reportedly common in the prairies of the valley, along with observances of grizzly bears (Ursus arctos horribilis) and gray wolves (Canis lupus).
A number of prairie dependent bird species once common to the Willamette Valley including Wilson’s snipe (Gallinago delicate), northern harrier (Circus cyaneus), short-eared owl (Asio flammeus), Western bluebird (Sialia Mexicana), and Western meadowlark (Sturnella neglecta) have suffered greatly from loss of habitat and have declined dramatically. The loggerhead shrike (Lanius ludovicianus) and black-billed magpie (Pica hudsonia) were also once present, but have been extirpated from the valley (Institute for Applied Ecology 2010).