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Alluvial Forest

Sites

River and stream floodplains in which separate fluvial landforms and associated vegetation zones are too small to distinguish.

Soils

Various alluvial soils including Altavista, Chewacla or Congaree.

Hydrology

Palustrine, seasonally or intermittently flooded.

Vegetation

Canopy

Canopy is a mixture of bottomland and mesophytic trees, including Liriodendron tulipifera (Tulip-tree), Liquidambar styraciflua (Sweet Gum), Acer rubrum (Eastern Red Maple), Fraxinus pennsylvanica (Green Ash), Betula nigra (River Birch), Juglans nigra (Black Walnut), Celtis laevigata (Southern Hackberry), Carya cordiformis (Bitternut Hickory), C. ovata (Common Shagbark Hickory), Platanus occidentalis (Sycamore), and Ulmus americana (American Elm).

Understory

Understory trees include Carpinus caroliniana (American Hornbeam), Ilex opaca (American Holly), Acer rubrum (Eastern Red Maple), A. floridanum (Southern Sugar Maple), A. negundo (Eastern Box Elder), and Asimina triloba (Common Pawpaw). Shrubs may include Euonymus americanus (Strawberry-bush), Lindera benzoin (Northern Spicebush), Aesculus sylvatica (Painted Buckeye), Cornus amomum (Silky Dogwood), Xanthorhiza simplicissima (Yellowroot), and Corylus cornuta (Beaked Hazelnut). Vines are frequently prominent, including Parthenocissus quinquefolia (Virginia-creeper), Toxicodendron radicans (Eastern Poison Ivy), Vitis spp. (Wild Grape), Smilax spp. (Greenbriar), Bignonia capreolata (Cross-vine), and Menispermum canadense (Moonseed).

Herb Layer

The herb layer is generally lush and diverse. Species include Erythronium umbilicatum (Dimpled Trout Lily), Claytonia virginica (Spring-beauty), Stellaria pubera (Star Chickweed), Solidago caesia (Axillary Goldenrod), Eurybia divaricata (Common White Heart-leaved Aster), Carex laxiflora (Sedge), Elymus virginicus (Common Eastern Wild-rye), Polystichum acrostichoides (Christmas Fern), Botrypus virginanus (Rattlesnake Fern), Uvularia sessilifolia (Straw-lily), Boehmeria cylindrica (False-nettle), Elymus hystrix (Common Bottlebrush Grass), Chasmanthium latifolium (River Oats), C. laxum (Slender Spikegrass), Geum canadense (White Avens), Verbesina alternifolia (Common Wingstem), Impatiens capensis (Orange Jewelweed), Corydalis flavula (Short-spurred Corydalis), Cryptotaenia canadensis (Honewort), Viola spp. (Violet), Arisaema triphyllum (Common Jack-in-the-pulpit), and Packera aurea (Golden Ragwort). Many places are heavily invaded by Lonicera japonica (Japanese Honeysuckle) and Microstegium vimineum (Japanese Stilt-grass) at the expense of native herbs.

Dynamics

Flood-carried sediment provides nutrient input to these communities, as well as serving as a natural disturbance factor. Small parts of forests may be eroded or disturbed by catastrophic floods. Beavers may occasionally create impoundments. Areas that have been cultivated or clear cut are generally dominated by Liriodendron tulipifera or Liquidambar styraciflua.

Associations

May grade into various mesic, dry-mesic, or dry upland forests, or to cliff communities. Borders river channel.

Comments

These communities occur on narrow floodplains of small streams or on large rivers where the floodplain is narrowed by bedrock. These are floodplains with limited differentiation of communities by depositional landforms. Flooding is of shorter duration and more variable than on larger floodplains, either because of the smaller watershed of small stream or because of the steeper gradient of confined floodplains of larger rivers. On large rivers, they occur only where the full width of the floodplain, rather than just one side, is narrow. Most of the canopy is of widespread species such as Liquidambar styraciflua and Liriodendron tulipifera, and upland species may be present, mixing with characteristic alluvial species such as Platanus occidentalis, Betula nigra or Celtis laevigata. Sites may vary due to different alluvial material and its effect on soil fertility but almost all alluvial sites are more fertile than surrounding uplands. Soils may be especially rich if adjacent uplands are on a mafic rock substrate.