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January 2000
Land along rivers, lakes, ponds, streams and wetlands are magnets for a great many wildlife species. The term we use for these areas is riparian, meaning of, on, or pertaining to the bank of a natural course of water. The Latin word riparius means bank. Riparian areas are part of the continuum from water to upland.
The boundaries of riparian habitats are not easily defined and vary in width according to the size and type of water body. In general, wildlife's dependence on food, cover and water in riparian habitats extends almost one thousand feet away from the water's edge. This is about one fifth of a mile.
Water, a requirement for survival, attracts wildlife. Also, the presence of water contributes to more plant growth, faster growth, and a greater diversity of plant species than occur on drier sites. The result is a complex structure that provides a variety of nesting and feeding opportunities for wildlife.
The health and biodiversity of these habitats increases as the width increases. Ninety percent of Maine's wildlife species use riparian habitats in some significant way during their life cycle. For forty percent of these species, riparian habitats are preferred. Bird life is richest at these meetings of land and water.
An essential function of riparian habitats is that of travel corridor. They provide connections across the landscape and allow movement between habitats. Species with large home ranges, such as black bear, use corridors; as do species that, as juveniles, disperse to populate other areas. Many furbearers such as mink, bobcat, and fisher concentrate their activity within three hundred and thirty feet from the water's edge. In winter, these animals can move easily in shallow snow on frozen waterways near the cover of riparian plants.
When development and forestry leave only a thin buffer of riparian plants, forest interior birds such as the ovenbird and the scarlet tanager are at a disadvantage. Dangers to forest interior birds' eggs and nestlings come from species attracted to forest edges, such as cowbirds, common grackles, blue jays, and American crows. A riparian forest buffer extending about seven hundred feet from the water satisfies the needs of most forest interior bird species.
Where people live next to water, there is constant, one might say chronic, disturbance to wildlife. Noises, such as doors slamming, and mere human presence are intrusions. The usefulness of the habitat is reduced, especially for shy and wary species, no matter what other attractions are present. For example, black ducks winter in salt marshes and, when disturbed, use precious energy flying or swimming away. Planted or preserved riparian buffers protect wildlife species from these types of disturbance.
Snags, which are dead and dying trees, are often abundant in riparian habitats. They are used as hunting perches by bald eagles and as nest sites by osprey. Pileated woodpeckers use large snags for nesting, and their nest sites are usually no farther than three hundred and thirty feet from water. In North America, eighty-five bird species rely on snags for nesting and roosting and many species of mammals, reptiles, amphibians and invertebrates use snags.
Riparian habitats with adequate plant cover benefit aquatic life. Plants help retain soil and reduce erosion of the banks into the water. They protect water quality by filtering sediments and non-point source pollutants from nearby uplands. Many animals in the water find cover beneath plants that extend beyond the bank. Insects, fruit, and leaves coming from these overhanging plants supply food for aquatic species. Woody material fallen into the water body creates structure, providing cover for fish and insects as well as basking sites for turtles, otters and waterfowl. Trees shade the water and keep it cool, an important factor for the health of aquatic ecosystems and an essential condition for trout and salmon.
Riparian areas with continuous forest cover, at least sixty-five to seventy percent canopy closure, and extending about one thousand feet from the water's edge would provide for all the values we attribute to them: wildlife habitat and water quality. Humans more frequently recognize the associated benefits, such as good fishing, great swimming, lovely recreational spots and beautiful experiences in nature. All life reaps rewards from generous, healthy riparian habitats.
By Nancy Coverstone (ncstone@umext.maine.edu), University of Maine Extension Educator in Androscoggin and Sagadahoc Counties
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