Geoscience Reference
In-Depth Information
zibethicus
), for example, is well known for
its ability to clear out cattails. Grass carp
and triploid white amur are herbivorous i sh
that graze on i lamentous algae, duckweed,
and other submerged plants (Lahring 2003).
However, these and other biological control
agents often are non-native species, and
their introduction must be considered with
due caution, so they do not become invasive
species as well. Government regulations
restrict the use of certain biological control
agents in some regions.
Figure 6-37.
Controlled prairie burning at a small
spring in the Flint Hills, Kansas, United States (see
Color Plate 6-37). Such burning is typically done in
latest winter or earliest spring to remove dead thatch
of previous year. Nutrients in the thatch are returned to
the soil to enrich spring growth. Photo by J.S. Aber.
From this brief discussion, it should be clear that
there is no simple way of eliminating invasive
wetland plant species. Most of the methods
produce only temporary or partial results. Physi-
cal methods are labor intensive and, thus,
expensive. Chemical methods should be used
sparingly in order to protect the environment,
and biological controls also have limitations.
Effective control of an invasive species generally
requires a combination of methods carried out
over a period of years or even decades.
reproduce vegetatively, removal must be
complete. Controlled burning is another
means to remove the above-ground plant
bodies during the dry (dormant) season (Fig.
6-37). All of these methods are labor inten-
sive and, in practice, generally lead only to
partial or temporary results.
• Chemical control with herbicides was once
the favored approach for dealing with
aquatic “weeds” (e.g. Wilson and Boles
1967). However, wetland application of her-
bicides is now considered a last resort or is
ruled out under many circumstances. Herbi-
cides may kill benei cial plants as well as
aquatic animals. The sudden death and
decay may deplete oxygen and lead to i sh
kills. Most chemical treatments are tempo-
rary and must be repeated periodically to be
effective (Whitley et al. 1999). Many herbi-
cides have a copper base, and repeated use
could lead to accumulation of copper in
toxic amounts (Lahring 2003). Given the sen-
sitive nature of wetland waters, it is best to
avoid chemical control as much as possible,
as the long-term consequences are poorly
known.
• Biological controls include a variety of
animals that may reduce or eliminate the
undesirable plant. Muskrat (
Ondatra
6.6 Summary
Wetland plants, known as hydrophytes, must
deal with a lack of oxygen in the soil as well as
potential l ooding and drying, lack of nutrients,
high acidity and salinity, and other limiting
factors. Many plants have responded with
special adaptations that allow them not only to
survive, but to thrive, under these stressful con-
ditions. Structural adaptations allow oxygen to
move from emergent plant leaves and stems into
submerged roots and rhizomes (aerenchyma,
pneumatophores, lenticels). For some hydro-
phytes, biochemical adaptations include the
ability to switch to respiration without oxygen
(anaerobic glycolysis) and tolerance for high
salinity. Many hydrophytes conduct C
4
photo-
synthesis, which has some distinct advantages
in aquatic environments, and some wetland
plants may reproduce both sexually and by veg-
etative growth.
Wetland vegetation is typically arranged in
distinct ecological zones
-
shoreline, emergent,
