Wet Alluvial Lands

Description

The reference state described is one of several vegetation communities within the Central Appalachian Stream and Riparian (CES202.609) and (in part) South-Central Interior Small Stream and Riparian (CES202.706). Due to the heterogeneity and the broadness of this provisional ecological unit, they are not intended to cover every situation nor the full range of conditions and species

BpS Dominant and Indicator Species
Symbol Scientific Name Common Name
PLOC Platanus occidentalis American sycamore
BENI Betula nigra River birch
ACNE2 Acer negundo Boxelder
ACRU Acer rubrum Red maple
CELA Celtis laevigata Sugarberry
LIQUI Liquidambar Sweetgum
FRPE Fraxinus pennsylvanica Green ash
LIRIO Liriodendron tulipifera Tuliptree
Disturbance Description
Flooding -- Flooding is the major process affecting the vegetation, with the substrate more rapidly drained than in flat flood plain areas. The distinctive dynamics of stream flooding and protected topographic position dominate the forming of the distinctive vegetation of this system. Not all of the factors are well known. Gradients of most of these rivers limit floods to fairly short duration. Flooding is most common in the winter, but may occur in other seasons particularly in association with hurricanes, tornados, or microbursts from thunderstorms. The sorting of plant communities by depositional landforms of different height suggest that wetness or depth of flood waters has significance. Flood waters have significant energy. Scouring and reworking of sediment make up an important factor in bar and bank communities. In addition to disturbance, floods bring nutrient input, deposit sediment, and disperse plant seeds. Most floods do not lead to canopy tree mortality. Flooding can act as a replacement disturbance in areas where beavers impounded a channel or in rare years with severe prolonged flood events. The most significant disturbance along small streams was wind. Two types of floods were modeled: occasional catastrophic floods due to beaver activity or other severe, prolonged floods, and more frequent repeated minor flooding (i.e., several minor floods within a 10 year period).

Winds affect streamside forests because of wet soils, less dense soil, and trees that are shallow-rooted. Canopy tree mortality from more common windstorms would have resulted in tree by tree or small group replacement. Wind throw formed the primary cause of mortality in bottomlands. Major storms or even hurricanes occurring at approximately 20 year intervals would have impacted whole stands. Tornado tracks can be found passing across uplands and bottomlands. Ice damage is an infrequent but potentially catastrophic disturbance.

Fire -- Fire regime group III (conspicuous and most frequent in stands with canebrake). Fire return interval varied highly. Except in canebrake, most fires were very light surface fires, creeping in hardwood or pine litter with some thin, patchy cover of bottomland grasses. Flame lengths were mostly 6 to 12 inches. Even so, fire-scarred trees can be found in most small stream sites except in the wettest microsites. Stand replacement fires are almost unknown in this type. Except where Native American burning was involved, fires likely occurred primarily during drought conditions and then often only when fire spread into bottomlands from more pyrophytic uplands. Trees may be partially girdled by fire in duff, followed by bark sloughing. While fire rarely killed the tree, this allowed entry of rot, which, in the moist environment, often resulted in hollow trees, providing nesting and denning habitat for many species of birds and animals. Surface fires occurred on a frequency ranging from about 3-8 years in streamside canebrake, streamside hardwood/canebrake, or pine, to 25 years or more in hardwood litter. Low areas having a long hydroperiod, islands, and areas protected from fire by back swamps and oxbows were virtually fire free. Fire effects were largely limited to top kill of shrubs and tree saplings less than 2 inches diameter, and formation of hollow trees.

Submodel