Geoscience Reference
In-Depth Information
l oating, and submerged
-
depending mainly on
growth position in relation to water level and
salinity. Many wetlands experience l uctuations
in water levels, so the shoreline and emergent
categories are subject to change through time.
Some wetland plants are able to grow in more
than one ecological zone, and some plants
found in wetlands also grow in dry, upland
settings.
Hydrophytes are used for regulatory pur-
poses in the United States to dei ne wetlands.
A wetland is indicated where an abundance
of obligate and facultative wetland indicator
species are present. However, the absence of
these species does not prove that a site is
not
a
wetland. For evaluating a site, the basic wetland
criterion is that more than half of the dominant
species are hydrophytic. The ability of a particu-
lar plant to thrive in the wild or under human
management depends on many factors and is
indicated by the plant hardiness zone, which is
based primarily on average annual minimum
temperature.
Introduced wetland plants may become inva-
sive if they possess some competitive advantage
compared with native plants. Invasive plants
tend to grow fast, disperse rapidly, and repro-
duce quickly. Wetlands have many such invasive
plants, which may cause substantial changes
in habitat conditions. Many methods exist to
control invasive wetland plants
-
prevention,
physical means, chemical control, and biological
agents. However, each of these methods has
limitations, and no simple means exists for elim-
inating invasive wetland plant species. Effective
control of an invasive species generally requires
a combination of methods carried out over a
period of years or decades.
