Info on Willamette Valley Riparian Habitat Issues and Approaches from OR Conservation Strategy

From OR Conservation Strategy

"Riparian habitats are those adjacent to rivers and streams or occurring on nearby floodplains and terraces. Riparian habitats are shaped and maintained through seasonal flooding, scour, and soil deposition. Floods replenish nutrients, recharge groundwater, and reset successional processes. Riparian habitats occur along rivers and streams at all elevations, from valley bottom floodplains to alpine torrents. Riparian habitats also include springs, seeps, and intermittent streams, and many low elevation alluvial floodplains confined by valleys and inlet.
Riparian habitats vary from sparsely vegetated areas to cottonwood gallery forests due to flood dynamics. Plant composition is influenced by elevation, stream gradient, floodplain width, and flooding events. Throughout most of the state, riparian vegetation is mostly dominated by deciduous trees and shrubs, such as bigleaf maple, alders, aspen, cottonwood, dogwood, willows and Oregon white ash. Conifers, such as pines and spruce, dominate some riparian woodlands at higher elevations. Riparian habitats in the Blue Mountains ecoregion are the most variable in Oregon, influenced by elevation and precipitation. In some ecoregions, riparian habitats include some riparian shrublands. In the East Cascades, riparian shrublands are dominated by deciduous shrubs, such as willows, creek dogwood, western birch or hawthorn."


Conservation Overview:
Riparian habitats often have high species diversity and are critical for wildlife. These habitats are important to species that prefer moist shrubby or forested habitats. Riparian areas provide essential wintering habitat and travel corridors for songbirds, mountain quail, white-tailed deer, and other wildlife. In arid areas such as the Blue Mountains and Columbia Plateau, riparian habitats can provide abundant insects, plants, and moisture throughout the year. Riparian meadows include natural spring-seep habitats that are extremely important for a wide variety of species, including greater sage-grouse chicks and butterflies.
In addition to providing habitat for birds and other wildlife, riparian habitats have important ecological functions. Healthy riparian vegetation protects banks from erosion, influences in-channel aquatic habitats, maintains favorable water temperature for fish through shading, filters runoff, and provides nutrients. Riparian vegetation creates meanders and increases habitat complexity in valley bottoms. In the Northern Basin and Range ecoregion, riparian vegetation can protect against scour from summer storms. Riparian habitats link upland and aquatic habitats. Upland habitats have a critical role in watershed function and affect riparian and aquatic habitats, particularly in drier, low-elevation sites.
Riparian habitats have declined from historic levels and are now greatly reduced in area and connectivity, especially those in low-elevation areas and valley bottoms. Development, logging, road building, agriculture and pasture use have degraded some riparian habitat directly through decreased riparian vegetation, increased sedimentation, and reduced large wood in streams. Runoff containing fertilizers and other contaminants can further impact habitat.
However, steps have been taken through Oregon’s planning and regulatory framework to address some of these issues. Cooperative restoration projects have benefited riparian-dependent species on forest and agricultural lands. In many cases, these efforts have focused on improving habitat quality in smaller, fish bearing streams. Streamside buffers implemented through the Northwest Forest Plan on public land and the Oregon Forest Practices Act on private land have improved riparian health on both public and private lands. On agricultural lands, Agricultural Water Quality Management Area Plans and Rules have been adopted across the state to address riparian conditions and other water quality issues. While each riparian rule is slightly different depending on the local area, the riparian rules generally require agricultural activities to allow establishment, development, and maintenance of riparian vegetation consistent with site capability to provide moderation of solar heating, filtration of overland flow, and streambank stability. The State expects to see improvements in riparian conditions on agricultural lands in the future and has initiated a riparian land condition monitoring program to track changes in riparian conditions over time. Riparian areas across the state will likely be conserved by a variety of measures including a combination of existing state and federal programs, both regulatory and nonregulatory. This will control degradation and improve water quality. Oregon Department of Environmental Quality’s completion of Total Maximum Daily Loads will also bring more specificity to recovery processes. For urban and rural residential development, some guidelines are provided through local land use ordinances adopted to address Statewide Planning Goal 5 requirements for riparian vegetation.


Willamette Valley: riparian forests have significantly declined with increasing development. Many streams now have only a thin strip of riparian vegetation, and some have none. Despite increasing emphasis on protection of riparian habitats and the formal establishment of the Willamette River Greenway, riparian habitats continue to decline.


Limiting factors to Riparian habitats:
Factor: Loss of riparian habitat, floodplain function, and habitat complexity: A high percentage of low-elevation and valley bottom riparian habitats have been lost. Riparian vegetation often is lost as habitat is converted to other uses. In several areas around the state, large cottonwood trees and gallery forest have been lost due to clearing and altered hydrological regimes. Development can restrict the natural ability of streams and riparian habitats to meander over time, limiting these habitats. Floodplains have been converted to other uses. Excessive removal of riparian vegetation can cause sedimentation that damages aquatic areas, loss of habitat complexity, and increased water temperatures that adversely affect aquatic habitat. Loss of streamside vegetation leads to bank erosion. Grazing and dam construction can degrade riparian habitats. Urban development has led to stream channelization and vegetation loss in some areas.
Approach: Restore riparian zones that will provide the full array of associated ecological functions. Use voluntary cooperative efforts (i.e., Conservation Reserve Enhancement Program) and incentive programs to conserve, maintain and restore riparian habitats on private lands. Identify and apply lessons learned from successful riparian restoration efforts on private lands to future projects. Develop tools and financial incentives to assist with streambank stabilization and decrease downstream soil movement. Improvements in riparian habitats and hydrology can also improve the quality of remaining wetland habitats. Maintain and restore riparian buffers and minimize impacts from road building on public lands. Where appropriate, permit beaver habitat usage to continue maintaining habitat complexity, particularly in the Coast Range and parts of eastern Oregon. Maintain channel integrity and natural hydrology. Where feasible, work to restore historic hydrological conditions. Ensure that adequate riparian vegetation remains following management activities, so riparian vegetation can continue to prevent erosion, preserve water quality, and promote water temperatures favorable for fish. Restore lost vegetation through planting of native trees, shrubs and ground cover. Manage for future sources of large woody debris. Maintain and/or expand existing tracts of cottonwood forest and all cottonwood trees greater than 20 inches diameter regardless of landscape context.



Factor: Loss of habitat connectivity: Riparian habitats are important movement corridors for wildlife, but habitat loss has resulted in reduced area and connectivity of riparian habitats.
Approach: Enhance or re-establish the extent and connectivity of existing riparian habitats.


Factor: Invasive plants: Invasive plants (such as knapweeds, knotweeds, reed canary grass, and thistles) degrade riparian habitats by competing with native plants. In the Columbia Plateau and Northern Basin ecoregions, pasture grasses and cheatgrass dominate the understory in some areas. In some riparian areas in the Northern Basin and Range, Columbia Plateau and East Cascades ecoregions, overgrazing has resulted in poor regeneration of hardwood trees and shrubs and change in plant species, including invasion by non-native grasses and forbs.
Approach: Emphasize prevention, risk assessment, early detection and quick control to prevent new invasives from becoming fully established. Control key invasive plants using site-appropriate tools, including mechanical, biological and chemical treatments. Use chemical treatment carefully and where compatible with water quality concerns, focusing on spot treatment during the dry season. In the Columbia Plateau and Northern Basin and Range, focus control at low elevation sites, unless near streams (seeds could flow downstream). Provide information to local governments and landowners about potential invasive plants. Where necessary (i.e., some areas in the Northern Basin and Range, East Cascades and Columbia Plateau ecoregions), develop and implement grazing management regimes that are compatible with riparian conservation objectives.