Wooded areas near streams or on the banks of streams are called riparian forests. They prevent erosion and trap sediment and runoff. They also cool water, provide underwater habitat and produce food for fish and wildlife. Eventually, the trees that are improving the health and quality of the waterway can be converted to useful wood products.
In rural Missouri, woody corridors often serve as buffers between cropland and pasture land and streams. In heavily forested areas, the border between riparian and upland forests is distinguished by a change in species and composition.
Riparian forests almost always occupy areas of moist, fertile soils. Streamside forests also tend to have larger trees with more dens and snags, and they are more likely to have a variety of tree heights. Typical riparian tree species include sycamore, cottonwood, bur oak, silver maple, ash, pecan and black walnut. Other common riparian plants include greenbriar, poison ivy, false rue anenome, stinging nettle and spicebush.
Historically, riparian forests protected most of the rivers and streams of the state. However, agricultural and urban development have reduced the amount of streambank that is now protected by trees, lowering water quality and reducing aquatic habitat.
When it rains, soil from unprotected areas washes into riparian areas. These areas are often referred to as creek and river bottoms. If there is nothing to slow or stop this soil, it will eventually end up in the stream itself. Too much sediment suspended in the water can reduce or block sunlight, which is necessary for the growth and reproduction of beneficial aquatic plants. Sediment on stream bottoms can disrupt the feeding and reproduction habits of fish and aquatic insects. Large sedimentary deposits can fill streams and increase the threat of flooding.
Riparian forests diminish the threat and effects of erosion and siltation. The protection begins with the tree canopy, which protects the soil from the hammering impact of rain. The leaf layer on the forest floor also protects the soil, and it acts as a sponge, soaking up water and slowing runoff from nearby fields and hills. Tree roots help prevent streambank erosion by holding soil in place.
Streamside forests also have a filtering effect. With slower runoff, more water soaks into the ground. Pesticides and fertilizers attached to soil particles aren't carried into the waterway. Filtering nitrogen and phosphorus is especially important because these can fuel excessive algal growth in the water, depleting oxygen levels to the point that fish and beneficial aquatic plants cannot survive.
Instead, these nutrients remain in the soil, where plants can absorb them and use them for growth and reproduction. The nutrients move up the food chain as animals eat the plants. This is called nutrient cycling.
The streamside forest releases nutrients, such as carbon, slowly as twigs and leaves decompose. These nutrients are valuable to the fungi, bacteria and invertebrates that form the basis of a stream's food chain.
Tree canopies of riparian forests also cool the water in streams. The difference in water temperature between shaded and unshaded portions of a stream can be as much as 10 degrees. This can affect the composition of the fish species in the stream. Channelizing or widening streams moves the canopy farther apart, decreasing the amount of shaded water surface and increasing water temperature.
Woody cover along streams provides important habitat for insects, crustaceans and other animals that comprise the diet of fish. Fish themselves use root wads and submerged logs for escape cover. Streams without this kind of cover usually offer poor fishing.
Wildlife benefit from riparian forests, as well. Streamside woodlands provide travel lanes, escape and nesting cover and den trees, as well as hard and soft mast for food. Reptiles and amphibians use fallen trees as basking areas. More than 35 bird species use riparian forests.
Because of their high fertility, many streamside woodlands are valuable for timber production, as well as for fish, water and wildlife. These forests produce high-quality, commercially valuable trees that can be converted to flooring, pallets, railroad ties, furniture and cabinets.
The Missouri Department of Conservation intensively manages riparian forests on the land it owns, but private landowners play the most important role in establishing and protecting riparian buffers. If you don't have woodlands along the waterways that run through your property, it's a good idea to establish them.
The presence of a riparian corridor where one didn't exist before immediately increases wildlife habitat and benefits a stream. It also starts a chain reaction of improvement. For example, as a tree grows taller, it provides more shade to cool stream water. At the same time, it produces a larger root system to stabilize the streambank and prevent erosion. As the tree continues to grow, it filters out more sediment while providing more escape and nesting cover for wildlife.
Forested buffers can be planted or allowed to seed naturally. A good start is to establish a strip at least 100 feet wide on each side of the stream. If the area is to generate itself naturally, there must be a source of lightweight, windblown seeds nearby. Cottonwood, silver maple, sycamore and ash all produce suitable seeds for a riparian corridor.
If there is no source of seed, or if you desire a specific mix of tree species, then planting trees is your best option. You'll have best success with native species. They are adapted to local soils and conditions. Plant a diverse mix of species that will provide both hard and soft mast for wildlife.Cost-share programs can help landowners establish and maintain riparian forest buffers. The Conservation Reserve Program (CRP) will pay up to 90 percent of the cost of establishment and provide annual payments for up to 15 years. The Conservation Department has programs that will pay 50 to 75 percent of the cost of tree planting.
You can improve an existing riparian corridor by widening it and filling in any gaps by planting or natural seeding. Conservation Department foresters can help you develop a management plan that improves the composition and structure of your forest.
Protect riparian buffers by keeping livestock away from them. Grazing results in streambank erosion and increased sedimentation. Livestock also can injure the root systems of trees and remove the forest understory, as well as the leaf layer that is so important for controlling runoff and filtering sediment.
It's unnecessary to remove trees that are in the stream or about to fall in. These provide underwater fish habitat. If log jams are a problem, leave the larger, stable portions and remove the unstable debris.
Keep heavy equipment at least 25 feet away from the streambank. If you're harvesting timber, be selective in the trees you take, and leave as many as possible. Leave snag and den trees to optimize wildlife habitat. Department foresters can provide more information about best management practices and additional advice on managing streamside zones.
Keeping our riparian forests healthy ensures that Missouri's streams continue to provide clean water and healthy aquatic habitats. While it may be a little heavy to carry in a tackle box, a tree-planting spade can be a handy tool for improving the fishing and the water quality in your local stream.
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