The 21st Century Community Schoolhouse's
Upland and Wetland Prairies Page
Upland Prairies
| ---The
upland prairies of Oregon’s Willamette Valley were once widespread
along the valley margins and in other well-drained soils. The upland prairies
are rare ecosystems with unique plant and animal communities consisting
of several grass species and forbs, or flowering plants. Many of these sites
could support forest vegetation, but remained an open prairie because of
the prescribed burning by the native Kalapuya Indians, who lived in the
region for the last 10,000 years. Frequent burning reduced the abundance
of trees and shrubs. ---After the Euro-American settlement in the 1830s, regular burning of prairie ceased and most of the valley was gradually developed for agricultural or urban reasons. As a result, native upland prairies, along with wetland prairies, now cover less than 1% of their former area, making them among the rarest of North American ecosystems. ---Remnants of these highly diverse, complex, and poorly understood ecosystems provide necessary habitat for many rare species. Remaining native upland prairies vary in size and quality. As of 1996, only five sites that contain relatively large areas of high or very high quality prairie and forty-two lesser sites existed |
Upland prairies are characterised by their unique mix of grasses and flowering plants called forbs. |
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Wetland Prairies
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Very similar in nature to upland prairies, these wet prairies are covered in water for much of the year, but produce colorful communities of forbs. |
---The
wetland prairies are noted for containing an abundance of grasses, such
as the tufted hairgrass and a rich biodiversity of native forbs. Lower
elevated spaces in these wetlands are typically inundated with water in
the winter months and serve as important features for flood control. They
are spread around and near the Willamette Valley, most of which are in
the flood plain of the Willamette River and the flood plain of its tributaries.
---Fire, as well as flooding, has shaped the Willamette Valley wetland prairies. Much of this area can support forest vegetation, but remained open because of periodic fires set by the native Kalapuya Indians to promote food plants and to ease hunting and travel. Summer drought dries both the soil and the vegetation, leaving the prairie flammable. These fires reduced the abundance of shrubs and trees, favored the abundance of grasses, such as the tufted hairgrass, and promoted a rich variety of native forbs. As a result of this ecosystem management by the Kalapuya, much of the Willamette Valley lowlands remained into the 1800s as wetland prairie. ---With population decline of the Kalapuya in the mid-1800s and with fire suppression, trees and shrubs increased in abundance, crowding out native prairie grasses and forbs. Prairies have also disappeared because of agricultural and urban development. |
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