Classification of Wetlands and Deepwater Habitats of the United States
Definition. The Class Scrub-Shrub Wetland includes areas
dominated by woody vegetation less than 6 m (20 feet) tall. The
species include true shrubs, young trees, and trees or shrubs that
are small or stunted because of environmental conditions. All
water regimes except subtidal are included.
Description. Scrub-Shrub Wetlands may represent a successional
stage leading to Forested Wetland, or they may be relatively
stable communities. They occur only in the Estuarine and
Palustrine Systems, but are one of the most widespread classes in
the United States (Shaw and Fredine 1956). Scrub-Shrub Wetlands
are known by many names, such as shrub swamp (Shaw and Fredine
1956), shrub carr (Curtis 1959), bog (Heinselman 1970), and
pocosin (Kologiski 1977). For practical reasons we have also
included forests composed of young trees less than 6 m tall.
Subclasses and Dominance Types.
Broad-leaved Deciduous. -- In Estuarine System Wetlands the
predominant deciduous and broad-leaved trees or shrubs are plants
such as sea-myrtle (Baccharis halimifolia) and marsh elder (Iva
frutescens). In the Palustrine System typical Dominance Types are
alders (Alnus spp.), willows (Salix spp.), buttonbush
(Cephalanthus occidentalis), red osier dogwood (Cornus
stolonifera), honeycup (Zenobia pulverulenta), spirea (Spiraea
douglasii), bog birch (Betula pumila), and young trees of species
such as red maple (Acer rubrum) or black spruce (Picea mariana).
Needle-leaved Deciduous. -- This Subclass, consisting of wetlands
where trees or shrubs are predominantly deciduous and needleleaved,
is represented by young or stunted trees such as tamarack
or bald cypress (Taxodium distichum).
Broad-leaved Evergreen. -- In the Estuarine System, vast wetland
acreages are dominated by mangroves (Rhizophora mangle,
Languncularia racemosa, Conocarpus erectus, and Avicennia
germinans) that are less than 6 m tall. In the Palustrine System,
the broad-leaved evergreen species are typically found on organic
soils. Northern representatives are labrador tea (Ledum
groenlandicum), bog rosemary (Andromeda glaucophylla), bog laurel
(Kalmia polifolia), and the semi-evergreen leatherleaf
(Chamaedaphne calyculata). In the south, fetterbush (Lyonia
lucida), coastal sweetbells (Leucothoe axillaris), inkberry (Ilex
glabra), and the semi-evergreen black ti-ti (Cyrilla racemiflora)
are characteristic broad-leaved evergreen species.
Needle-leaved Evergreen. -- The dominant species in Needle-leaved
Evergreen Wetlands are young or stunted trees such as black spruce
or pond pine (Pinus serotina).
Dead. -- Dead woody plants less than 6 m tall dominate Dead
Scrub-Shrub Wetlands. These wetlands are usually produced by a
prolonged rise in the water table resulting from impoundment of
water by landslides, man, or beavers. Such wetlands may also
result from various other factors such as fire, salt spray, insect
infestation, air pollution, and herbicides.
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