Marshes, Playa Wetlands, Wet Meadows, and Fens - Mountains and Plains: The Ecology of Wyoming Landscapes - page 79

hummocks, fen margins, and shallow channels with
running water. 38

as allelopathy (which has been difficult to demonstrate
except in laboratory experiments).
Although both reed canarygrass and common reed
are native to north America, they are also native to
europe. Such a widespread distribution can be attrib-
uted to great genetic variation within the species. At
some point during the past century, seeds from euro-
pean populations of both species were introduced to
north America, where the resulting plants interbred
with native populations. As it turns out, the hybrids
appear to be more aggressive invaders than the native
populations. thus, where reed canarygrass and com-
mon reed appear to be invading wetlands, most likely
the plants involved are euroAmerican hybrids. Slight
genetic changes can greatly improve a plant's ability to
compete with its neighbors.
invasive hybrids have also formed in cattails. two
native species occur throughout much of north Amer-
ica—broadleaf cattail and narrowleaf cattail. Until
recently, the narrow-leaved species was so rare in mid-
western and western states that some botanists, after
observing how its range was expanding, came to think
of it as an introduced invasive plant. 46 indeed, narrow-
leaf cattail has expanded its range. More important,
though, the two native species—now growing together
more commonly than ever before—are hybridizing. the
sterile offspring, known as hybrid cattail, spread rapidly
by rhizomes and are highly invasive. 47 Very likely, euro-
pean genes are a contributing factor.
An especially worrisome invasive plant in marshes
is purple loosestrife, a colorful forb that grows 3 or 4
feet tall. though still rare in Wyoming, this european
species has overwhelmed native wetland plants in
midwestern and eastern states. Seasonal wetlands are
most vulnerable to invasion, because loosestrife seed-
lings establish on bare sediments during dry periods.
Preventing the spread of localized invasives like purple
loosestrife is generally more feasible than trying to
reduce large populations once they are well established.
Also, early control is less damaging to the environment.
Biological control of purple loosestrife shows some
promise.
in addition to invasive species and the loss or degra-
dation of wetlands, there are now concerns about the
effects of climate change. Warmer, drier conditions
likely will result in shallower water, causing seasonal

Management Issues and Future Challenges

Wetlands worldwide have long suffered degradation
and outright destruction caused by myriad factors,
including the perceived need for drainage and water
diversion, the accumulation of excess nutrients and
contaminants, and excessive grazing by livestock (see
chapter 4). 39 in Wyoming, 35-40 percent of the original
wetlands have been lost, and elevated levels of ground-
water contaminants are sometimes present. 40 Generally,
mountain wetlands have been less affected because
water is more readily available and the duration of graz-
ing is shorter. 41 Also, pollutants are less widespread in
the mountains. Peat mining has severely disrupted
some fens in the mountains of colorado, 42 but that has
not taken place in Wyoming.
invasive plants have become a severe problem in
many wetlands. 43 ecologists think of wetlands as “land-
scape sinks,” that is, low places on the landscape where
water, nutrients, sediments, and salts accumulate, and
where water levels fluctuate—all conditions that favor
weedy plants. Various eurasian species are common
in Wyoming's wet meadows, namely, canada thistle,
creeping bent grass, creeping foxtail, Kentucky blue-
grass, and timothy.
Some invasive wetland plants are now thought of
as natives. Kentucky bluegrass is an example, as it has
been in north America long enough to be viewed as
naturalized. in contrast, some species that are veritable
natives behave like invasive species in altered wetlands.
For example, reed canarygrass expands rapidly in wet-
lands created by irrigation. Such habitats could have
been invaded by introduced species, but native plants
often colonize the irrigated lands first. the species does
provide good forage, but it tends to reduce the plant
diversity of the areas where it becomes the dominant
plant. 44 Another invasive native, common reed (also
known as phragmites), grows to more than 6 feet tall
and is rapidly invading wetlands, especially at lower
elevations in adjacent states. 45 this invader is thought
to benefit from chemicals produced and released by
the plants that suppress the growth of other species,
thereby facilitating its spread—a phenomenon known