The scrubby low shrubs, grasses, and box elders frequently lining Vermont rivers may appear ordinary, but the strips of land they grow on are among the most important pieces of property in our state.
Known as riparian buffers, these corridors of trees, shrubs, and groundcover plants provide multiple benefits to wildlife, humans, and the rivers themselves. Specifically:
A vegetated buffer with its plant trunks and stems, leaf litter, and uneven ground topography will slow overland run-off, which allows the buffer to filter out sediments, nutrients, pathogens, and toxins. These pollutants are broken down by and incorporated into plants, soil, and microorganisms.
A canopy of trees along a stream bank keeps the water cooler, which helps sensitive aquatic species, including some fish.
Insects falling from overhanging vegetation provide a principal summer food source for certain fish species.
Tree and shrub growth at the edge of the water provides overhanging branches, stable undercut banks, and in-water snags that offer stable substrate for macro-invertebrates, such as caddis flies and mayflies, and protective cover for fish species.
Many amphibians, reptiles, waterfowl, raptors, songbirds, and mammals, including mink and otter, thrive in well-vegetated corridors along streams.
Stream bank erosion, common in Vermont, is a natural process. Through the science of fluvial geomorphology the study of landscapes formed by water processes weve learned that many streams in Vermont have lateral instability, meaning they move back and forth across their valleys at more rapid rates than stable streams. This lateral instability is primarily due to a lack of deep-rooted, dense vegetation on the stream banks.
Naturally stable streams in broad valleys or otherwise unconfined settings have access to their floodplains. Energy from the stream can then be dissipated as the water flows over the banks and into the floodplain a process that allows the water to spread out and slow down, thereby reducing the downward erosion on the stream bed during floods. However, even these types of streams benefit from the existence of woody vegetation on their banks and in their floodplains. Such vegetation further dissipates the energy associated with flowing water. Streams that are unstable and lack access to their floodplains, then, experience more downward erosion of their stream bed. Riparian vegetation helps these streams by binding the stream banks with roots to protect against the strong force of water.
Some unstable streams have eroded down their channel beds, or have become incised, meaning they cannot access their original floodplains. This may be caused by human efforts to straighten the channel, gravel extraction, or floodplain encroachments (fill placed in the active floodplain). As a result, their stream banks bear considerable stress during high water. Due to this increased stress on the stream banks, the channel begins to erode outward, or laterally. The channel over-widens considerably, and eventually fills with sediment. Over time a new narrow channel forms again in this wide channel bed and new floodplains develop to either side of the new channel at a lower elevation. The cumulative effects of stream bank and bed erosion and the resulting channel adjustments cause loss of property, loss of aquatic and wildlife habitat, decreased water quality, and greater risk of flood-related damage.
Streamsides often represent high-risk areas for development even if located above flood elevation. Public and private investments, including culverts and bridges, are at risk when stream dynamics are not considered. Riparian buffers are cost-effective protection against flooding, shoreline erosion, and the lateral movement of channels.
Fortunately, restoration of a riparian buffer is a fairly simple process. The easiest, but slowest, method of restoration is simply moving the impact (possibly a tilled field or trail) away from the stream and allowing the area to naturally revegetate. Over several years, a mix of grasses, trees, and shrubs will establish themselves. A more effective restoration process involves the active planting of native riparian species, such as red-osier dogwood, willow, fern, maple, and birch.