Environmental Engineering Reference
In-Depth Information
TABLE 8.1.  Plant Categories Used in Wetland Delineation
Category
Symbol
Definition
Obligate wetland plants
OBL
Plants that occur almost always (estimated probability >99%) in wetlands
under natural conditions, but which may also occur rarely (estimated
probability <1%) in nonwetlands. Examples: Spartina alterniflora) and
Taxodium distichum .
Facultative wetland plants
FACW
Plants that occur usually (estimated probability >67-99%) in wetlands, but
also occur (estimated probability >1-33%) in nonwetlands. Examples:
Fraxinus pennsylvanica and Cornus stolonifera .
Facultative plants
FAC
Plants with a similar likelihood (estimated probability 33-67%) of occurring
in both wetlands and nonwetlands. Examples: Gleditsia triaconthos and
Smilax rotundifolia .
Facultative upland plants
FACU
Plants that occur sometimes (estimated probability 1-33%) in wetlands, but
occur more often (estimated probability >67-99%) in nonwetlands.
Examples: Quercus rubra and Potentilla arguta .
Obligate upland plants
UPL
Plants that occur rarely (estimated probability <1%) in wetlands, but occur
almost always (estimated probability >99%) in nonwetlands under natural
conditions. Examples: Pinus echinata and Bromus mollis .
(a)
(b)
Figure 8.6.  Wetland plants: (a) marsh grass ( Spartina alterniflora) ); (b) bald cypress ( Taxodium distichum ). Source : U.S. National
Oceanic and Atmospheric Administration (2005).
tive plants (FACs), facultative upland plants (FACUs),
and obligate upland plants (UPLs). The characteristics
of the five plant categories are given in Table 8.1. To
meet the wetland vegetation requirement, more than
50% of the dominant species in a delineated wetland
area must be OBLs, FACWs, or FACs. Species lists of
plants in these categories can be found in USACE
(1987). Marsh grass ( Spartina alterniflora) ) and bald
cypress ( Taxodium distichum ), both shown in Figure 8.6,
are plant species that are almost always found in
wetlands.
long enough during the growing season to develop
anaerobic conditions in the upper soil layers that favor
the growth and regeneration of hydrophytic vegetation.
Most soils, including hydric soils, are composed pre-
dominantly of minerals, such as quartz, feldspars, and
clay minerals. However, hydric soils commonly have a
buildup of organic matter at the soil surface, which can
make the surface horizon dark colored. If the organic
matter content (measured as organic carbon) is greater
than 20-30% of the soil's weight, and this organic-rich
layer is more than 40 cm (1.3 ft) thick, it is considered
an organic soil. Peat is composed mostly of recognizable
plant fragments that are only partly decomposed; muck
contains highly decomposed organic matter. When
8.2.2.2  Soils.  Wetland soils, called hydric soils , are
defined as soils that are saturated, flooded, or ponded
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