(John A. Christy, Oregon Biodiversity Information Center)
Wet prairies are one of Oregon's rarest wetland types. Most occur at lower elevations on bedrock or clay loam soils that have a seasonally perched water table. These sites usually dry out by late spring but depressions may retain water well into the summer. Shallow soils over bedrock, and rock outcrops are included as part of this habitat because they are often intermixed with clay soil sites and the same vegetation may occur on both substrates (e.g., Isoetes nuttallii, Triteleia hyacinthina). There is also some overlap with vernal pool vegetation. Wet prairie in the Willamette and Umpqua valleys are habitat to several rare species of plants. Although best known for tufted hairgrass (Deschampsia caespitosa), wet prairies contain many other species of grasses, sedges and herbs. Before flood control, wet prairies on the Columbia River bottoms were flooded for one or two months every year during the annual "spring freshet" fueled by snowmelt in the Columbia Basin. Most wet prairies have been drained, farmed, grazed, or overrun by exotic species.