Riparian Landscapes - Mountains and Plains: The Ecology of Wyoming Landscapes - page 45

Chapter 4 Riparian Landscapes

Streamside landscapes are highly valued real estate—
ecologically and economically. they account for a mere 2
or 3 percent of the land area, but an estimated 75 percent
of native animal species depend on them at some time
during the year for food, water, and shelter. 1 Animals also
move along the riparian corridors in both directions,
often passing through otherwise hostile environments
(fig. 4.1). in addition, riparian zones filter sediments and
nutrients, thereby improving water quality, and during
the spring they store water in alluvial sediments that sus-
tain streamflow late in the summer. Domesticated ani-
mals often congregate in riparian zones, as do people.
cities, towns, roads, and cultivated fields usually are
located there, and, not surprisingly, most riparian zones
at low elevations are privately owned.
From the smallest rivulet at high elevations to the
largest river in the lowlands, the riparian landscape can
be viewed as a continuum. creeks that begin with the
melting of alpine snow cross the full range of climatic
conditions, changing from incised streams flowing
over cobbles and gravel to meandering rivers underlain
by sand or mud. the environment changes gradually
along the waterway, except at occasional beaver dams,
waterfalls, and rapids, or at entrances to canyons. Some
streams are long, originating in the mountains; others
are short, such as those that begin as seeps or springs
in the lowlands. creeks and rivers with headwaters at
high elevations have peak flows in the spring, at the
time of snowmelt. new channels may form during
floods. Also, old trees topple into the water along erod-

ing banks, and new sediments are deposited as bars or
on floodplains. Such developments lead to a continu-
ously varying riparian mosaic of woodlands, shrub-
lands, meadows, marshes, sand bars, and mudflats.
Physical factors that determine the nature of stream-
side vegetation include elevation, climate, the steep-
ness of the terrain, soil type, channel sinuosity, and
the width-to-depth ratio of the stream. other factors
are beaver dams, grazing by large mammals, and water
diversion projects for agriculture, municipalities, and
industry. Like the vegetation, riparian soils are highly
variable across a floodplain and are strongly influenced
by hydrologic factors. commonly, there are overlapping
lenses of gravel, sand, and silt, indicating the locations
and velocity of former stream channels.
Separating riparian habitats from other kinds of
wetlands—namely, marshes, fens, wet meadows, and
playas (see next chapter)—is commonly done by con-
sidering water movement. Rivers and streams have
free-flowing, oxygen-rich surface water most of the
year. exceptions are ephemeral streams that usually
flow only in the spring and early summer. in contrast,
nonriparian wetlands are usually associated with still
or slow-moving water, and the bottom sediments are
more likely to be anaerobic for a longer time during the
year. in general, all wetlands have soils that are wet long
enough during the year to enable the growth of plants
that require large amounts of water. Such species are
known as hydrophytes and are used to define the nature
and extent of wetlands for legal purposes. 2

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