Riparian Areas 6

Riparian areas “Most people camp too close to the creek to make good coffee.” 6 — Rube Long he physical, chemical, and biological channel and floodplain, and is connected to makeup of a stream relates to the sur- upstream and downstream ecosystems. Trounding physical features of the watershed Riparian habitat is a combination of three and its geologic origin. Looking at these features areas. Each is distinctive and contributes to the helps us understand stream-watershed relation- entire ecosystem. ships and allows managers to predict the effects Aquatic area: The aquatic area of streams, of human influences on different streams. lakes and wetlands is generally wet. During dry Think of the uplands of a watershed as the periods, aquatic areas have little or no water sides of a funnel, and the stream flowing from flow. Any side channels or oxbows containing the mouth of the funnel. The riparian area is the freshwater ponds are included in this area. sides of the spout surrounding the stream. The Riparian area: The riparian area is a terres- riparian area is the green zone of plants along the trial zone where annual and intermittent water, a stream. Water, nutrients, and sediments from high water table, and wet soils influence vegeta- across the uplands move down- tion and microclimate. hill to support this lush Area of influence: This and productive area. is a transition area between a Streams and riparian area and upland riparian areas develop cover. An area of influence together, each affecting has soil moisture and is the development of the characterized by a noticeable other. Headwater streams change in plant composition and are small, and the riparian abun- areas that surround them are dance. relatively narrow. Larger streams Trees in Vocabulary and rivers flood more often, and this area aquatic area floodwaters carve out wide flood- contribute aquifer plains. The plant communities that shade, leaves, area of influence develop along the edge of the stream are woody debris and edge effect generally distinct from those that cover the insects to a stream. floodplains broader, and somewhat drier floodplains. In the Pacific Oregon Forest Plants along the stream influence the Northwest, the area Practices Act entire stream ecosystem. Riparian areas of influence in- riparian area (Figure 6) have several unique properties. A cludes ground riparian management riparian area is linear, has a water transport covers, shrubs and areas understory trees understory Oregon Department of Fish & Wildlife Riparian areas • 161 (usually deciduous) Stream food chains depend on organic debris on the floodplains, for nutrients. In small headwater streams, 99% of and canopy trees the energy for organisms comes from the vegeta- (usually coniferous) tion along the stream, and only 1% from photo- on hillsides. This synthesis. The leaves, needles, cones, twigs, stair-stepping of wood, and bark dropped into a stream are a vegetation provides a storehouse of readily available organic material variety of wildlife that is processed by aquatic organisms and re- habitat. turned to the system as nutrients and energy. A diverse population of insects depends on this varied food base. Between 60% and 70% of Role of riparian vegetation the debris is retained and processed in the head- Riparian plant communities (Table 1) provide waters by bacteria, fungi, insects, and abrasion, cover for aquatic and terrestrial animals. Shade with very little leaving the system until it has created by the riparian vegetation moderates been at least partially processed. water and air temperatures. This vegetation limits Riparian areas have a high number of edges water contamination, slows water velocities and (habitat transitions) within a very small area. The filters and collects large amounts of sediment and large number of plant and animal species found debris. Uncontrolled sediments can kill fish and in these areas reflects habitat diversity. Since destroy spawning areas. they follow streams, riparian areas are linear, Figure 6. Riparian Habitat 162 • The Stream Scene: Watersheds, Wildlife and People Oregon Department of Fish & Wildlife increasing the amount and importance of edge backwaters act as reservoirs to hold surplus effect. Extensive edge and resulting habitat runoff until peak floods are past. This controls diversity yield an abundance of food and support and reduces downstream flooding. Floodplains a greater diversity of wildlife than nearly any also spread the impact of a flood over a larger other terrestrial habitat. area as vegetation helps collect debris and sediment. Composition of riparian plant communities Floodplains depends on the water pattern (fast or slow mov- Floodplains are an important part of a ripar- ing or dry or wet periods). Both wet and dry ian area. Floodplain vegetation that shades or phases are necessary in this area to complete the directly contributes material to a stream is con- stream’s nutrient cycle and food chain. Flooding sidered part of the riparian area. is critical to the exchange of nutrients and energy between the stream and the riparian area. When healthy, vegetated banks in the riparian area act as natural sponges. They help main- Flooding is critical to the tain soil structure, allow increased infiltration, and reduce bank erosion. exchange of nutrients and Vegetated streambanks also contribute to aquifer (groundwater) recharge. Precipitation is energy between stream and filtered through the riparian soils and enters underground reservoirs called aquifers. Good riparian area. cover slows the flow and increases percolation into underground aquifers. Stored water is then Stream channels rely on natural flooding available during drier periods to maintain and patterns. Frequency of flooding and groundwater improve minimum flow levels. A major benefit supply are the major factors controlling the of this aquifer recharge is maintenance of year- growth of floodplain trees. Floodplains and round streamflow. Table 1. Functions of Riparian Vegetation As They Relate to Aquatic Ecosystems Riparian Vegetation Site Component Function Above ground- Canopy and stems • Shade—controls temperature and instream photosynthetic productivity above channel • Source of large and fine plant detritus • Source of terrestrial insects In channel Large debris derived • Control routing of water and sediment from riparian • Shape habitat—pools, riffles, cover vegetation • Substrate for biological activity Streambanks Roots • Increase bank stability • Create overhanging banks—cover Floodplain Streams and • Retard movement of sediment, water and floated organic low-lying canopy debris in flood flows. Source: William Meehan et al., Influences of Riparian Vegetation on Aquatic Ecosystems With Particular References to Salmo- nid Fishes and Their Food Supply, 1977, p. 137. Oregon Department of Fish & Wildlife Riparian areas • 163 Riparian vegetation uses large amounts of Amphibians and reptiles are another indica- water in transpiration. Often, vegetation needs tor of riparian quality. Nearly all amphibians the most water during the period of lowest depend on aquatic habitats for reproduction and streamflow. At these times, vegetation may overwintering. Certain turtles, snakes, and lizards actually reduce streamflow. also prefer riparian ecosystems. Animal populations in riparian areas are Wildlife in riparian areas affected by the size and diversity of available Riparian ecosystems provide the essentials of wildlife habitat: food, water and cover. In gen- Amphibians and reptiles are eral, the area within 200 yards of a stream is used most heavily by wildlife. In western Oregon, of another indicator of riparian 414 known species of wildlife, 359 use riparian ecosystems extensively and 29 species are tied quality. exclusively to this area. While riparian areas cover less than 1% of the land in eastern Oregon, 280 of 379 species use this area extensively. habitat. Adjacent land-use activities may have a Riparian areas provide migration routes and direct effect on wildlife population size within a corridors between habitats for many animals. riparian area. Woody plant communities in the riparian area Fish populations can be an indicator of provide cover, roosting, nesting and feeding watershed and riparian ecosystem health. Large areas for birds; shelter and food for mammals; woody materials, such as fallen trees and limbs, and increased humidity and shade (thermal create pools and protective cover, which are cover) for all animals. necessary components of fish habitat. This Birds are the most common and conspicuous woody debris also increases the diversity of form of wildlife in a riparian ecosystem. In this invertebrates, which are a basic part of the food important breeding habitat, as many as 550 chain on which fish depend. breeding pairs have been found per 100 acres. Bird density is just one indicator of the productivity of a riparian area. People in riparian areas Mammals of all sizes are found in riparian Since the land along streambanks and floodplains areas. Many rodents are parts of various food is often fairly flat, riparian areas are attractive chains. Some, such as beaver, may modify ripar- locations for roads. Roadbuilding may increase ian communities. The effects of beavers on a sedimentation, which can adversely affect watershed can be both positive and negative. aquatic life, especially fish. Runoff from roads Their actions change watershed hydrology as can carry oil, antifreeze, and other contaminants well as damage cover. A beaver dam

Load more