Marshes, Playa Wetlands, Wet Meadows, and Fens - Mountains and Plains: The Ecology of Wyoming Landscapes - page 68

in wetlands but can tolerate moist upland habitats as
well. in all kinds of wetlands, plants in the sedge fam-
ily (cyperaceae) are very common, with 47 percent of
the 174 species of that family in Wyoming classified as
obligate wetland indicators. the grass family (Poaceae)
has more species (275) in the state than the sedge fam-
ily, but far fewer are confined to wetlands (8 percent).
Among the shrubs, willows are especially common in
mountain wetlands and in riparian zones, with 11 of the
state's 41 species (27 percent) found only in wetlands.
other wetland shrubs include greasewood, resin birch,
and shrubby cinquefoil. numerous sedges, grasses, and
other graminoids and forbs are found in all kinds of
wetlands (fig. 5.4). trees, though, are largely riparian or
found on lake shores. 5
Mosses and algae also can be an important compo-
nent of wetland vegetation. A study of 17 fens in the
Medicine Bow Mountains documented 30 species of
mosses, compared to 105 species of vascular plants. in
Yellowstone national Park, a survey of 166 fens found
44 species of mosses and 254 species of vascular plants.
notably, mosses in fens often cover as much of the
ground surface as vascular plants. Algae are less con-
spicuous but are an important source of food for her-
bivorous aquatic invertebrates. 6
Among the vertebrates, amphibians have the most
obvious affinity for wetlands, because the adults need
water for breeding and their tadpoles are confined to
water. of the 12 species of salamanders, frogs, and
toads that live in Wyoming, 10 are closely associated
with water. 7 Birds are the most conspicuous wetland
vertebrates, with 82 of Wyoming's 434 species. 8 over
half of those (44) are summer residents only. 9 of the
118 species of mammals in Wyoming, approximately
35 (30 percent) use wetlands for more than a source of
water. 10 they include the beaver, muskrat, moose, river
otter, raccoon, meadow jumping mouse, meadow and
water voles, 3 species of skunk, 16 species of bats, and
8 species of shrews.
As noted, wetlands sometimes dry out, or at least
the water level fluctuates dramatically. this variation
seems unfortunate for many wetland species, but there
are benefits. Drying excludes predatory fish and allows
the development of food webs composed entirely of
invertebrates, including mollusks, crustaceans, and
insects. 11 Saline wetlands in the region can be rich

in invertebrates, providing a critical food source for
migrating waterfowl and shorebirds. Also, during low-
water seasons, some plants and animals are favored that
are less tolerant of high water. Fluctuating water levels
enable both groups of species to survive. Water diver-
sions intended to keep wetlands filled to a constant
depth may not be advisable, though the impulse to do
so is understandable if most nearby wetlands have been
drained, or if they have been severely altered in some
ot her way.

Surviving in the Wetland Environment

An abundance of water would seem to be an unalloyed
benefit in semi-arid climates, but prolonged soil satu-
ration creates oxygen deficiencies that many species
cannot tolerate. 12 those that do survive have various
adaptations. to illustrate, microbial organisms derive
their energy in ways that do not require oxygen, using
nitrates, sulfates, iron, manganese, and even carbon
dioxide instead. 13 By changing these elements from oxi-
dized to reduced forms, they also create the chemical
environment characteristic of hydric soils. For example,
reduced iron and manganese are water soluble and are
leached from the soil, leaving white or pale gray hori-
zons (known among soil scientists as gleyed horizons ).
Similarly, much of the sulfur is reduced to hydrogen sul-
fide, the marsh gas with an odor of rotten eggs. Reduced
nitrogen gases are commonly lost from wetland soils,
so nitrogen can be a limiting factor for plant growth.
Similarly, carbon—which exists in many organic forms
in hydric soils—can be lost as methane gas. even so, the
rate of carbon accumulation in undisturbed wetlands
usually exceeds the rate of loss. 14
Woody plants generally avoid the problems of anaer-
obic soils by growing in microenvironments where oxy-
gen is more readily available, such as raised hummocks
and wetland edges, or on slopes where groundwater
moving through the soil supplies sufficient oxygen.
Mosses use the same strategy by growing on the wet-
land surface. Some herbaceous vascular plants that are
rooted deeper in the saturated soil obtain their oxy-
gen via aerenchyma, a spongy tissue in their stems and
roots through which oxygen diffuses from the atmo-
sphere above the water to the respiring root cells. this
exchange can be more than passive diffusion, as some