From
the air, the edges of a stream appear as bright green tracks furrowed into
the forest floor. That's because grasses, shrubs, and trees flourish in
the damp, fertile soil of the banks and floodplains that border the
stream.
This is the riparian zone, a protective margin of vegetation that keeps the water clear and cool for the creatures of the stream. It is also important to almost all of our forest animals, which come not only to drink, but to find food, shelter, and hiding places. In summer, shade from the vegetation along the water's edge moderates temperature, humidity, and light. In winter, thickets of trees and vines buffer the area from harsh winds. This provides a protected habitat for many woodland animals.
Natural Buffers
Alder,
maples, willows, and many other plants stabilize the stream banks and
prevent erosion from storms and snow melt. Their leaves intercept much of
the rain before it reaches the ground, returning it to the atmosphere as
water vapor. Storm water runoff carrying potential natural pollutants such
as silt, nitrogen, and phosphorus, is absorbed and used by the plants
before it enters the stream. Soils also store excess water underground,
releasing it slowly over time to prevent downstream flooding. Pesticides
and other human-generated pollutants may be retained by the soils long
enough for bacteria to break them down into harmless compounds.
Birds build their nests in trees along the bank from mud and twigs
gathered along the
shore. They feed on the seeds and berries of streamside shrubs or on
aquatic insects. Deer and moose come to the stream to drink. In winter,
they travel its frozen corridors to their feeding grounds and yard in its
sheltered valley. Weasels, mink, skunks, and mice scurry beneath the shade
of the streamside forest to avoid the notice of owls, hawks, and other
sharp-eyed predators. Night-prowling raccoons leave tiny leprechaun
footprints in the muddy banks as they hunt for crayfish and freshwater
mussels.
Flying
insects that drop into the water from overhanging branches are quickly
devoured by predatory fish like trout and salmon (Fishing lures are
designed to imitate this riparian food supply that splashes into the
stream from above.) Ultimately, the largest fish in a river is dependent
on leaf litter from the riparian zone. An alder leaf that is swept into a
stream in Eustis is broken down and recycled as it moves downstream. It
feeds an insect that soon is gobbled by a small fish which eventually is
eaten by a trout that in turn nibbles at the hook of a fly fisherman on
the lower Kennebec.
bank, abuts a public resource, the water. What we do on our own land
affects what happens far beyond our property line. Even a narrow gash in
the riparian zone, made by a stream crossing for cows, a log skidder, or
an all-terrain vehicle, opens the stream to runoff of silt and pollutants
from the land. Silt clouds the water, scratches the delicate gills of
fishes, and smothers aquatic insects and fish eggs. A build-up of silt
makes the river bed more shallow and prone to overflow its banks in a
heavy storm. Phosphorus, nitrogen, and other nutrients washed in with the
soil cause noxious algae blooms.
Where
trees and shrubs have been cleared entirely from the water's edge, erosion
turns the stream mud brown. Without a shady canopy, the water becomes too
warm for fish like salmon and trout. If the food supply of leaf litter and
falling insects stops, many aquatic animals either starve or move to a
more favorable environment. When we breach this wall of vegetation we
begin a chain of destruction that threatens habitats, food chains, and the
quality of the water far downstream.