Bottomland Hardwood Management
Species/Site Relationships

Pines are relatively "elastic" in their site requirements and are adaptable to a variety of site conditions. Pines can survive and prosper on sandy sites with good to excessive drainage, and they can grow on some poorly drained sites. However, most desirable species of hardwoods have more demanding site requirements and will survive and grow well only on a comparatively narrow range of sites. Furthermore, stem grade or quality is a major consideration for hardwoods and may be greatly influenced by site conditions.

Bottomland Hardwood Sites

The term "bottomland hardwoods" generally refers to hardwoods associated with current floodplain sites. Soils on these sites are from recent alluvium, are relatively young, generally have good water relations, and may be highly productive for hardwoods.

Floodplain sites in the South are somewhat arbitrarily divided into major and minor bottomlands. This difference may be obvious in the size of the stream, since major bottoms are usually associated with large rivers. However, another important difference may be in the nature of the deposition that occurs. The alluvium deposited in major river bottoms may come from hundreds or even thousands of miles away and is composed of materials of all textural classes (and perhaps several kinds of minerals). In minor bottoms, the alluvial deposits are of local origin and may vary less in textural class and mineralogy. For these reasons, major bottoms are most often, although not always, more productive than are minor bottoms.

Bottomland hardwoods occur primarily in the Atlantic and Gulf Coastal Plain divisions of the Coastal Plain Province. Their occurrences are determined by the nature of the geologic materials that are sedimentary in origin and relatively easily eroded, as opposed to the more consolidated geologic material of the mountain and piedmont regions. In geologic times, when the climate was much warmer and wetter, ancient streams first eroded away vast amounts of material to form stream valleys and then began the process of deposition, which continues with the current streams.

There are about 30 million acres of bottomland hardwoods in the South. This area is less than one-half the area at the time of European settlement. Most of the reduction is a result of conversion to agricultural uses, and much of the loss has been in the Mississippi River system.

Site Variations

Each topographic feature listed below may occur several times...and not necessarily in the order shown. There is a notable difference between bottomlands found in the Atlantic Coastal and Gulf Coastal Plain in that ridge, and swale topography is far more common in the Atlantic Coastal region. This variation is due to differences that occurred during the formation of floodplains.

Bars or point bars are formed when the concave section of stream banks erodes and the sediment is deposited downstream on an opposite convex area of the stream channel. With time and increased deposition, the bar may become a mud flat and may eventually be raised to the level of the current front or natural levee.

Fronts generally represent the best sites for tree growth in the floodplain. These natural levees are formed when streams overflow their banks and there is rapid deposition. These areas are typically the highest sites with the best surface and internal drainage. They are the most productive areas, and virtually all desirable bottomland hardwood species can be grown on these sites.

Ridges are nothing more than old fronts and are generally considered to be the second best sites for hardwoods. These areas vary in elevation from 2 to 15 feet above flats, but 2 to 3 feet elevation is more common. Drainage may not be quite as good as on fronts, and since the soils are older, fertility may be lower than on fronts. By comparison, soils in ridges are more coarse-textured than those in flats, and drainage is better. Species suitability on these sites would be limited primarily by the typical absence of pioneer species such as yellow poplar.

Flats represent a significant change in site quality, as compared to fronts and ridges. These are typically broad, smooth areas between ridges or between ridges and fronts. The soils are predominantly clays, and the drainage class usually varies from poorly drained to somewhat poorly drained; standing water is usually absent most of the growing season. There may be slight elevation differences, and variations classified as "high flats" and "low flats" can often be recognized based on drainage patterns. Flats account for the largest area within the floodplain, and overall, the number of desirable species and growth on these sites will be less than on fronts and ridges.

Sloughs are shallow depressions originating from old stream channels that are almost filled with sediment. These are low areas with poor drainage, and heavy clay soils and standing surface water is typically present well into the growing season. These sites generally support the growth of lower quality and less desirable species, e.g., overcup oak and water hickory.

Swamps are also old stream channels, but the channel is deeper and surface water is typically present year-round. Species suitability in these areas is extremely restricted by the water, with baldcypress and water tupelo typical.

Species Occurrence

There are other wet sites that support hardwood growth but are not associated with stream floodplains. These sites are typically covered with hardwoods because they are not suitable for growth and development of pines. Generally these sites are not as productive as floodplains, and the hardwoods are of lower quality. Examples of these sites are coastal swamps and muck swamps. They may support a variety of hardwoods, but baldcypress and tupelos are typical.

In major stream bottoms, specie associations will vary, depending on the stage of succession. Even though not all the species are desirable, a review of the more common combinations is presented. This listing, with reference to natural patterns, gives insight to the need for active management of these areas if the most desirable species are to be grown and maintained.

On bars, willow is the major pioneer species, but if the land is high enough or if it can become established between high water levels, cottonwood will come in. Willow and cottonwood need mineral soil to become established, but willow is more tolerant of water. Both species can withstand sediment deposition, and if it continues, front land will be formed and willow and cottonwood may be replaced by river-front species.

On fronts, a typical association following cottonwood is composed of elm, sycamore, sweet pecan, sugarberry, boxelder, and sweetgum. This river front association is not final, and the successional association will depend on how the stand is replaced. If replacement is rapid (caused by humans or natural disaster), a red oak-sweetgum type may occur if advance regeneration is present. If replacement is slow, the stand will retrogress to a boxelder-sugarberry or boxelder-hackberry-silver maple association. As the site matures, it may again be occupied by an association composed primarily of sweetgum and red oaks.

Species composition on the flats is extremely variable. On low flats, overcup oak, water hickory, and cypress often dominate. Almost pure stands of overcup are common. On high flats, the most common association is composed primarily of elm-ash-sugarberry with other species (such as Nuttall oak, willow oak, and red maple) being common in the mixture. Nuttall oak and willow oak on occasion will be major components of the stands.

On ridges, species composition depends largely on past events and past treatments. The elm-ash-sugarberry type is the most common association; but if the site is opened rapidly and advance regeneration is present, it can be replaced by a sweetgum-red oak type composed of water oak, willow oak, cherrybark oak, Shumard oak, and other minor species, in addition to sweetgum. Without management this type will revert to the elm-ash-sugarberry association through natural succession.

If sloughs are near the stream and/or sedimentation occurs rapidly, good stands of black willow often occupy the site. If sedimentation continues, the willow will be replaced by the elm-ash-sugarberry type. On sites where sedimentation occurs slowly, e.g., at some distance from the stream, overcup oak, water hickory, green ash, and persimmon are the tree species that most often follow the willow.

The baldcypress-water tupelo type is most common in the swamps of major river bottoms. Depending on depth and duration of flooding, other tree species that sometimes occur include swamp tupelo, water elm, Carolina ash, water hickory, swamp laurel oak, and overcup oak.

Minor stream bottoms are, in many ways, just a smaller version of major bottoms -- they exhibit the same topographic features, and most of the other same species occur there, although not necessarily on the same topographic position. Species that occur only on ridge positions in major bottoms often occur on flats in the minor bottoms. River birch is most often the pioneer species on new land such as bars and mud flats. Species composition is extremely diverse on the fronts or natural levees and may include yellow poplar, American beech, sycamore, spruce pine, sweetgum, cherrybark oak, Shumard oak, water oak, swamp chestnut oak, and several species of hickory.

Although flooding still occurs, autogenic forces control natural succession and species occurrence on these front sites. Typical species occurring on better drained flats and ridges of minor bottoms include sweetgum, cherrybark oak, water oak, swamp chestnut oak, American elm, and hickories. On less well- drained flats, the major species include overcup oak, willow oak, Nuttall oak, swamp laurel oak, persimmon, green ash, sugarberry, and red maple. Species composition occurring in sloughs of minor bottoms will vary, depending on duration of flooding. Cypress, swamp tupelo, and water elm are common where flooding duration is longest, and overcup oak, water hickory, and persimmon will also occur where flooding is not as severe. Swamps containing cypress and water tupelo do occur on the floodplains of minor bottoms, but the cypress and swamp tupelo types are more common.

Implications for Use or Management

In addition, a knowledge of species-site relationships is essential for successful management of bottomland hardwood stands, whether the objective is timber, wildlife, or a combination of the two. Reforestation or restoration projects are likely to be a complete failure if the species are not matched to the sites.

It is important to note that bottomland ecosystems are not static. The biotic and abiotic components will change over time with or without the influence of humans. What is here today will not be here 100 years from now or perhaps even 10 or 20 years from now. For example, black willow stands do not live very long -- they will be replaced, and new ones will not be created except by disturbance -- natural or man-made.

The ecological processes and species/site relationships discussed in this publication have implications for making management decisions that could resolve or reduce conflicts over use of the bottomland hardwood resources. These areas are diverse and thus, over large areas, a great variety of uses and interests can be accommodated. You can use active management to maintain or increase compositional and structural diversity to meet the objectives of ownership.

Literature Cited

By Dr. Andrew W. Ezell, Extension Forestry Specialist, and Dr. John D. Hodges, Professor of Silviculture, Department of Forestry.

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Publication 2004
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director