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.