Red River Large Floodplain Forest

This floodplain forest system is specifically restricted to the main stem of the Red River in the West Gulf Coastal Plain and Upper West Gulf Coastal Plain of southwestern Arkansas, adjacent Texas, and Louisiana. Several distinct plant communities can be recognized within this system that may be related to the array of different geomorphic features present within the floodplain. Some of the major geomorphic features associated with different community types within the system include natural levees, point bars, meander scrolls, oxbows, and sloughs. The vegetation generally includes forests dominated by bottomland hardwood species and other trees tolerant of flooding, including bald-cypress and water tupelo. Herbaceous and shrub vegetation may also be present in certain areas. Some canopy trees that may occur in examples of this system include Betula nigra, Platanus occidentalis, Fraxinus pennsylvanica, Celtis laevigata, Liquidambar styraciflua, Ulmus americana, Nyssa biflora, Populus deltoides, Salix nigra, and Quercus texana. Components with longer hydroperiods may contain Quercus lyrata, Gleditsia aquatica, Carya aquatica, Nyssa aquatica, and Taxodium distichum. Smaller trees include Quercus similis, Quercus sinuata var. sinuata, Ulmus crassifolia, and Carpinus caroliniana. Shrubs include Alnus serrulata, Forestiera acuminata, Planera aquatica, Cephalanthus occidentalis, Ilex decidua, Crataegus viridis, Sabal minor, and Itea virginica. Herbs are limited due to the length of flooding, but some examples are Boehmeria cylindrica, Mikania scandens, and Lysimachia radicans. Typical floating aquatic plants include Nelumbo lutea, Nuphar advena, Nymphaea odorata, and Lemna minor.

The vegetation generally includes forests dominated by bottomland hardwood species and other trees tolerant of flooding, including Taxodium distichum and Nyssa aquatica. Herbaceous and shrub vegetation may also be present in certain areas. Riverfront sites, and newly exposed or disturbed sites, are occupied by Platanus occidentalis, Populus deltoides, Salix nigra, Betula nigra, Acer negundo, and Fraxinus pennsylvanica. Some portions of the system are seasonally flooded, and these may contain species such as Quercus lyrata, Carya aquatica, Taxodium distichum, Nyssa aquatica, Nyssa biflora, Quercus phellos, Gleditsia aquatica, and Planera aquatica. Less frequently flooded areas may be dominated by numerous hardwood species, including Liquidambar styraciflua, Quercus nigra, Quercus phellos, Quercus shumardii, Quercus macrocarpa, Quercus michauxii, Quercus falcata, Carya illinoinensis, Celtis laevigata, Ulmus alata, Ulmus americana, Ulmus crassifolia, Ulmus rubra, Gleditsia triacanthos, Nyssa sylvatica, and Fraxinus pennsylvanica. In addition, Juniperus virginiana, Pinus taeda, and, to a lesser extent, Pinus echinata may also be found in the canopy. A midstory component may include young individuals of the overstory, as well as Quercus similis, Quercus sinuata var. sinuata, Carpinus caroliniana, Ostrya virginiana, Acer rubrum, Sassafras albidum, Maclura pomifera, and Morus rubra. The wetland shrub Cephalanthus occidentalis may dominate some open sites within the floodplain. In addition to these species, shrubs such as Alnus serrulata, Forestiera acuminata, Crataegus viridis, Crataegus marshallii, Callicarpa americana, Ilex decidua, Sabal minor, Itea virginica, and Arundinaria gigantea may be found in the understory of forests, as well as the exotic shrub Ligustrum sinense. Numerous woody vines may be encountered, including Smilax rotundifolia, Brunnichia ovata, Berchemia scandens, Lonicera japonica, Nekemias arborea (= Ampelopsis arborea), and Toxicodendron radicans. Herbaceous species may be present in the understory of forest, occur as marshy areas, or occupy herbaceous-dominated sites on areas less frequently flooded. Saururus cernuus, Nymphaea odorata, Rhynchospora spp., Carex spp., Dichanthelium spp., Chasmanthium spp., Juncus spp., Leersia sp., Geum canadense, Sanicula canadensis, Woodwardia areolata, Boehmeria cylindrica, Mikania scandens, and Polygonum spp. are among the herbaceous species that may be commonly encountered in this system. Typical floating aquatic plants include Nelumbo lutea, Nuphar advena, Nymphaea odorata, and Lemna minor (Elliott 2011). The forests of the Red River are thought to differ from those of other systems because of the greater presence of "riverfront" species (P. Faulkner pers. comm.). More information is needed, including a review of the affiliations of associations to this system versus West Gulf Coastal Plain Large River Floodplain Forest (CES203.488).

Some of the major geomorphic features associated with different community types within the system include natural levees, point bars, meander scrolls, oxbows, and sloughs (Sharitz and Mitsch 1993). The "flatwoods" of the upper terraces within the floodplain are a different system. The geology is Quaternary alluvial deposits. Landforms include the floodplains of the Red River and its major tributaries. Some local topographic variation exists and includes terraces and oxbows. The soils include loams and other bottomland soils (Elliott 2011).

This system is maintained by natural large river hydrological processes (e.g., meanders, flooding, backswamps, natural levees). Occasional, long duration flooding can cause the loss of canopy over large areas. This canopy decline and reproductive failure can create late-seral open stands. Duration of flooding varies with the placement of a site in the landscape and is a dominant process affecting vegetation on a given site. Meandering rivers are dynamic and change course, eroding into the floodplain and depositing new point bars, thus creating new habitat for early-seral plant communities. Changes in hydrology due to the activities of beaver are also an important ecological process in bottomland hardwood forests. Beaver activity causes changes in hydrology, and this is an important ecological process in bottomland hardwood forests; the effects are poorly understood at the landscape level, especially in the presettlement context. Beaver impoundments kill trees (sometimes over large areas) but may also create open water habitat, cypress-tupelo stands, or cause stand replacement. In addition to periodic flooding, the dominant ecological process in bottomland hardwood forests is the formation of windfall gaps, which can occur on the local scale (a single mature canopy tree) as well as the landscape scale (tornadoes or hurricanes). When canopy trees fall, seedlings in the understory are released and compete for a spot in the canopy. This leads to dense areas of herbaceous and woody vegetation in windfall gaps of all sizes. This is a major process in forest regeneration in bottomland hardwood forests. This system is also bordered by a number of upland communities from which fire would have occasionally burned down into the bottoms, especially in drought years.

The primary threats to this system are conversion to agriculture and developed land uses, repeated timber harvesting, alteration of natural hydrological processes (e.g., dams, levees, draining, ditching, dredging), intensive silvicultural practices, fragmentation, and water pollution. Viable forest patches must be large enough to allow for processes that maintain floral and faunal species composition and structure at the landscape scale (Harris 1989, Sharitz and Mitsch 1993). Fragmentation leads to disruption of natural processes such as plant succession, nutrient cycling, and litter accumulation. Increases in edges over interior of patches favor common and weedy species over specialists. In terms of generalists, this includes white-tailed deer, raccoons, opossums, and brown-headed cowbirds. These species affect others through activities such as increased browsing, nest predation, etc. (Harris 1989). Edge effects occur around forest patches, and are more intense and disruptive in small patches, and with more abrupt edges. Patches with natural edges are probably fairly functional, but sharp artificial edges lead to increased mortality of the trees and more severe deterioration of ecological processes. Intact natural forest patches buffered by areas of low-intensity forest management tend to be in better condition than those adjacent to agricultural land (Harris 1989). The most significant potential climate change effects over the next 50 years include alteration of waterflow, caused by periods of drought alternating with more intense storms.

This system is restricted to the main stem of the Red River in the West Gulf Coastal Plain and Upper West Gulf Coastal Plain of southwestern Arkansas, adjacent Texas, and Louisiana. Its range is conceptually coincident with the vast majority of Subsection 234Ai of Keys et al. (1995), excluding the portion of 234Ai within TNC Ecoregion 42 (Mississippi River Alluvial Plain). Its range is also coincident with EPA Ecoregion 35g (Red River Bottomlands) (EPA 2004). The portion of the Red River to the west (231Em of Keys et al. 1995) is treated as part of West Gulf Coastal Plain Large River Floodplain Forest (CES203.488).