Yazoo - Low Clayey Backswamp Ridge Forest

Description

Removal of the pre-settlement natural communities of the Yazoo Basin began long before thorough studies and investigations were initiated. Modifications to the Basin’s natural hydrodynamics and drainage patterns coupled with location-specific land use histories have further complicated species-site relationships. Such complexity across the Yazoo Basin will likely be reflected in much variability in vegetation composition and structure of local forest stands (Stanturf et al., 2001). Accordingly, reference conditions for this site are currently under review. They are perceived to consist of mature forest stands that support a diverse mix of southern bottomland hardwoods adapted to the poorly drained clayey soils and geomorphic setting of low ridges and rises within backswamp environments. Once assigned, the reference community will not represent the pre-settlement forest community, but it should identify an assemblage of naturally occurring species that reflects and contributes to regional biodiversity and local forest ecology. Implicated in the latter is that the “local” geomorphic features and drainage patterns of this soil-site environment should not have been drastically altered or removed (e.g., land leveled or extensively ditched and drained).

Based on former forest surveys and available literature, the sweetgum – willow oak (or red oaks) association is provisionally selected to represent reference conditions based on its perceived commonality or dominance on this site (see Putnam and Bull, 1932). A second forest type reported on this site is the sugarberry – American elm – green ash association or a variant of the type. It is important to note that many of the same species are shared among the two types (Putnam, 1951; Eyre, 1980) with differences mainly occurring in the concentration and abundance of shade intolerant versus shade tolerant components (Eyre, 1980). The widespread occurrence of the sugarberry – American elm – green ash community is often attributed to former land use practices that removed commercially valuable trees, typically sweetgum and oaks, while leaving behind species of little commercial value (Putnam and Bull, 1932). Based on the preceding coupled with the propensity of the type to replace other plant communities due to shade tolerance (see Clatterbuck and Meadows, 1993; Allen et al., 2001; Oliver et al., 2005), the sugarberry – American elm – green ash type was not considered to be the representative community of this ecological site. This position will be critically reviewed and evaluated during the next phase of ecological site development, the verification stage.

The return or transition pathway from the altered states (currently, only States 2 and 3) back to reference conditions is intended to represent the suite of hardwood species that, reportedly, frequently to occasionally occur and are favored in management on this site. Realistically, it may not always be possible to return to a “perceived” reference state from a former altered condition. While planting and establishing trees appropriate for a site may be possible, achieving restoration of the understory and other system functions are challenges that may never be realized (Stanturf et al., 2001; Flinn and Vellend, 2005).

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Description

The Greentree Reservoir (GTR) state is provisionally included in this description due to the level of hydrologic manipulation and management that is generally pursued. Additionally, these structures have widespread distribution and occurrence throughout the Southern Mississippi River Alluvium and have been developed and established on this ecological site.

The principal function and purpose of most GTRs within MLRA 131A is to provide reliable flooded habitat for migrating and wintering waterfowl in one of North America’s irreplaceable migratory corridors, the fabled Mississippi Flyway. The extensive losses of forested habitat coupled with the draining of wetlands and construction of flood control projects throughout the MLRA have made these reservoirs particularly attractive to wildlife, recreationists, and natural resource managers (Fredrickson and Batema, 1992). They occur on both public and private lands (Wigley and Filer, 1989). In general, GTRs consist of floodplain forests that have been leveed, water control structures established, and a water supply constructed to flood targeted locations during tree dormancy, which generally occurs from late fall to late winter. These management units are typically positioned in environments that can be effectively flooded or impounded to a shallow depth, consist of predominantly clayey soils, and support mature bottomland hardwoods with a concentration of red oaks such as Nuttall, willow, water, and cherrybark with pin oak (Quercus palustris) increasing in importance in the northern portions of the MLRA. Red oaks are heralded for providing an energy-rich food source for some waterfowl species. Important soft mast food sources include elm, ash, tupelo (Nyssa spp.), and red maple (Acer rubrum) (Fredrickson and Batema, 1992; Fredrickson, 2005).

The composition and maturity of many forest stands within GTRs likely support characteristics that resemble reference conditions. However, hydrologic regimes and hydroperiods of many GTRs are managed intensively every year with targeted flooding beginning and ending (i.e., drained) on predetermined dates, often coinciding with waterfowl hunting seasons. In many instances, water drawdown is delayed due to logistical limitations and extends into the growing season (Wigley and Filer, 1989; Fredrickson and Batema, 1992). This annual rigor in maintaining water levels differs greatly from natural, periodic flooding regimes and has led to unanticipated single-species and community-level stressors, particularly in areas where this level of yearly management has occurred for more than a decade (Fredrickson and Batema, 1992). Some of the reported impacts include basal swelling of trees, reduced tree vigor, tree mortality, changes in plant composition to predominantly flood tolerant species, poor acorn production, poor tree regeneration, increased windthrow, crown dieback, tree cankers, a higher incidence of insect infestations, and even a decrease in waterfowl usage (Wigley and Filer, 1989; Fredrickson and Batema, 1992; Fredrickson, 2005; Hertlein and Gates, 2005; Heitmeyer et al., 2024). Notably, management of some GTRs have been modified over the years to mimic more natural, periodic flooding cycles with shortened hydroperiods to reverse these types of impacts. Still, the uncertainties of community-level responses and conditions within these impoundments have prompted inclusion of this state.

Note that this state mainly pertains to established GTRs. If there is intent to develop one of these management units, then all Federal and State statutes and regulations pertaining to wetlands and the Nation’s waters and waterways must be followed. All associated regulatory reviews and permits should be completed and obtained before construction activities are pursued.

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This state consists of two very different community phases and management approaches. Community Phase 3.1 represents forest management and production on this site. A distinguishing feature of this phase is the level of management intensity designed to maximize merchantable goals. Various silvicultural methods are available for selection, and these are generally grouped into even-aged (e.g., clearcutting, seed-tree, and shelterwood) and uneven-aged (e.g., single tree, diameter-limit, basal area, and group selection) approaches (Meadows and Stanturf, 1997). Depending on the method selected, different structural and compositional characteristics of the stand may result. Removal and control of community associates are typically a critical element of production goals. These actions may result in different community or “management phases” (and possibly alternate states) depending on the methods used and desired results. Finding the appropriate approach for a given stand and environment necessitates close consultation with trained, experienced, and knowledgeable forestry professionals. If there is a desire to proceed with this state, it is strongly urged and advised that professional guidance be obtained and a well-designed silvicultural plan developed in advance of any work conducted.

Community Phase 3.2 represents conditions of many stands that have incurred indiscriminate timber harvests (e.g., heavy cutting or diameter-limit harvests of select species) and opportunistic regrowth following such harvests (i.e., no management at any period). Some stands may continue to support a few desirable species and quality stems, but in many instances, affected stands will be comprised of mostly shade tolerant species or trees of desirable species that are defective and fail to meet their maximum potential. (Because of the intensive management required to rehabilitate affected stands, this community phase warrants elevation to a standalone state. This should be considered in future iterations of this site’s development.)

Although this site is well suited for forest production, seasonal wetness imposes severe limitations for some forest operations. The principal management concerns are equipment limitations, plant competition, and seedling mortality. Seasonal wetness and periods of heavy precipitation can impose limitations on heavy equipment usage. If possible, equipment operations are best conducted during drier periods of the year, which minimizes soil damage, compaction, erosion, and helps to maintain productivity. A seasonal high water table that includes ponding or inundation for long periods can kill recently planted seedlings, especially if they are not adapted to withstand these conditions. Additionally, these soils have high shrink-swell potential, which causes deep, wide cracks to develop during droughty periods (USDA-SCS, 1990; USDA-NRCS, 2004; USDA-NRCS, 2006b). Exceedingly long dry periods could cause desiccation of exposed roots, which is another potential source of seedling mortality (Goelz, 2001).

An important caveat of this state is its representation of forest conditions that have retained full site production potential. Currently, transitional pathways to this state originate from another forested state (States 1 and 2), only. Former land uses (alternate states) that result in altered conditions of the soil environment (e.g., land leveling, ditching and drainage) may deleteriously affect predicting and planning for species site selection, tree productivity, and possibly survival of the targeted species. State 7 (Forest Recovery) is representative of forest establishment and growth on locations where soil compaction and reduction of nutrients have occurred due to former land practices. Once a previously affected location has recovered its site potential, transition to this state may be possible. That potential transition is still under review and is currently not shown or addressed in the state and transition model.

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This state is representative of the dominant land use activity on this ecological site, agriculture production. Principal crops grown on these soils are rice (Oryza sativa) and soybeans (Glycine max) with secondary crops consisting of small grains such as wheat (Triticum aestivum) and cotton (Gossypium hirsutum) (Snipes et al., 2005). Specialty crops (e.g., fruits, vegetables, and tree nuts) may be grown locally depending on local hydrology and the soil-site environment.

Suitability of this ecological site to row crops ranges from well suited to poorly suited depending on local flood regimes, drainage patterns, and the targeted crop. These soils have moderate to high available water capacity, organic matter content, and natural fertility with soil reactions that range from very strongly acid to moderately alkaline (Bruce et al., 1958; USDA-SCS, 1990; USDA-NRCS, 2004; USDA-NRCS, 2006b). Applications of fertilizer and lime may not be a necessity everywhere or in every circumstance as these soils are naturally high in phosphorus and potassium and pH levels are generally within a favorable range. Soil tests should be conducted to determine fertilizer, lime, and nitrogen needs on a specific field and for a given crop (USDA-SCS, 1990). Management concerns are largely centered on seasonal high water tables, very slow permeabilities and runoff, delayed plantings, soil compaction under equipment traffic, development of a plow pan, and poor tilth due to the clayey texture. Areas that are prone to flooding or extended periods of wetness may not be suitable for small grain crops or to crops that require planting in April and May. Management measures to ameliorate some of these issues may include conservation tillage or management system; subsoiling to breakup plow pans for dry-land crops (e.g., soybeans); restricting tillage to appropriate soil moisture content; and establishing a drainage system or network in problematic areas (USDA-SCS, 1990; USDA-NRCS, 2004; USDA-NRCS, 2006b). Of caution, subsurface drainage systems (e.g., pipes or tiles) may not be effective in every situation due to very slow permeability or localized flooding (USDA-SCS, 1990). Major components that producers generally develop and plan are proper selection of crop cultivar, pest control, cropping system, tillage methods, nutrient management, and water management (Snipes et al., 2005). Key practices of some cropping systems often include two or more crops grown in a multiyear rotation, which has been documented to disrupt pest cycles. Leaving crop residue on the surface can help to maintain tilth, fertility, and organic matter content – all critical elements of soil quality and health. For monoculture cropping systems, the implementation of well-designed pest and nutrient management systems are imperative (Pringle et al., 2017). (For assistance, interested parties are advised to visit their local NRCS Field Office.)

Three separate management phases comprise this state: Conservation Management (4.1), Transitional Conservation Management (4.2), and Conventional Management (4.3). The three phases consist of varying tillage methods and approaches to soil health management systems.

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The gently sloping to undulating ridges of this site typically adjoin level surfaces. This site is often bordered by soils of varying textures and drainage characteristics. Accordingly, inconsistencies in wetness and dryness, ease of operation, and production or yields may occur across a cropped location. An increasingly common practice consists of land forming or leveling surface irregularities into a predetermined and engineered, uniform slope. This practice removes drier and higher features, which are then used to fill wetter and lower positions (e.g., depressions or swales) across the targeted area. Advantages of land leveling may include reduced hazards of erosion and runoff rates, improved surface drainage, and enhanced distribution and conservation of irrigation water. Disadvantages of the practice is a churning of various surface and subsurface materials (former soil horizons) that no longer occur in a predictable or regular pattern. Organic matter content in the surface layer is generally low, and the surface tends to crust and pack after heavy rains (USDA-NRCS, 2006b). One potential hazard that appears to be emerging in some areas is the need for managing surface water runoff. As both irrigated and stormwater runs off leveled fields at uniform rates, surface water tends to collect cumulatively and simultaneously, which places tremendous demands on local drainage systems. Without “in field” structures (natural or artificial) to stagger runoff, the downslope (or lower) ends of some fields tend to back flood thereby contributing to more flooding overall in local watersheds (personal observations).

Immediately following land leveling, the constituent elements of soil health are likely to be absent. In some areas, producers have initiated practices such as applying organic residues (e.g., poultry litter) or growing rice crops for one to two years to rapidly boost fertility and introduce organic matter (via rice biomass) in the surface layer. Over time, the full complement of the management (or community) phases of State 4 may be possible on land leveled fields. They are not repeated or indicated here.

Currently, this state serves as an endpoint in the state and transition model because the ability to predict vegetation response when transitioning to a different state is no longer possible without soil-site investigations for each area of interest. The former soils of this ecological site, including surface and subsurface horizons, will have been redistributed as particles among other former soils depending on the depth of the initial “grade cuts” and leveling efforts.

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This state is representative of areas that have been converted to and maintained in pasture or grassland. In 1991, the soils of this site were placed in Pasture Suitability Group 4a for the State of Mississippi. This group consists of somewhat poorly and poorly drained acid and nonacid clayey soils with a root zone of 20 to 40 inches. Limitations of this state are mainly associated with a seasonally high water table and the flooding of areas that are located near active tributaries or prone to back flooding. High water tables over long durations will restrict root growth and establishing plants in particularly wet locations may prove challenging. These soils are suited to most commonly grown forage species except bahiagrass (Paspalum notatum), crimson clover (Trifolium incarnatum), and some cool season annual forage plants. Note that bahiagrass and crimson clover do not respond well where soil reactions are above 6.5 (Houck, 2009; Young-Mathews, 2013). Overall, forage production is considered moderate to high when adequately fertilized and properly managed. Lime may not be a necessity everywhere or in every circumstance. Soil tests should be conducted to determine fertilizer, lime, and nitrogen needs for a specific location (USDA-SCS, 1990).

Given that this ecological site occurs on poorly drained, clayey soils, some forage operations may experience multiple wetness events in a single year. Management concerns are mainly centered on soil compaction due to grazing (USDA-NRCS, 2006b), and overgrazing can lead to numerous bare spots and muddy conditions that effectively reduces or destroys plant establishment and productivity. Planning or prescribing the intensity, frequency, timing, and duration of grazing will be very important on these wetter soils. Of caution, some annual and perennial winter plants naturally growing in wet locations (e.g., sedges, rushes, and some forbs) may be an additional challenge as these are often unpalatable or toxic if consumed.

Flood-prone areas may limit the type of forage suited for this site. In areas that flood on a regular basis, implementing management actions such as planting or overseeding appropriate cool season forage varieties (e.g., ‘Marshall’ ryegrass, Lolium perenne ssp. multiflorum; also known as annual ryegrass) into established warm season grasses at heavy forage rates have been observed to help protect riparian areas from detrimental river or stream scouring (personal observations by Rachel Stout Evans, contributing author). Initiating such remedial actions aid in the recovery and reestablishment of preferred warm season forage following seasonal flooding. (Note that herbicide resistant varieties could be problematic and may warrant reconsideration. Please consult with local NRCS Field Offices for assistance.) Where permissible, a system of artificial drainage or water control structures may be in place to facilitate continued forage production and grazing during wetter periods. Note that the higher elevations of this site may serve as important protection areas for the storage of harvested forage or the holding of livestock when wet or flooded conditions occur on the lower, adjoining flats.

Establishing an effective pasture management program can help minimize degradation of the site and assist in maintaining growth of desired forage. An effective pasture management program includes selecting well-adapted grass and/or legume species that will grow and establish rapidly; maintaining proper soil pH and fertility levels; using controlled grazing practices; mowing at proper timing and stage of maturity; allowing newly seeded areas to become well established before use; and renovating pastures when needed (Rhodes et al., 2005; Green et al., 2006).

This state consists of four community phases that represent a range of forage management options and pasture and hayland condition scenarios. Options range from establishing a forage monoculture for haying to a broad mixture of forage species for production and grazing. It is strongly advised that consultation with local NRCS Service Centers be sought when assistance is needed in developing management recommendations or prescribed grazing practices.

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This state is representative of forest recovery in areas that were once under former intensive land use such as long-term row crop cultivation. Characteristics that distinguish this state from other forest states on this site include a suite of soil-site properties that reportedly affect tree growth such as higher soil bulk density due to compaction, presence of a plow pan, lower organic matter content, and reduced fertility (Baker and Broadfoot, 1979; Groninger et al., 1999). Two community phases are provisionally recognized for this state. Community Phase 7.1 represents natural colonization of tree and shrub species without management. Community Phase 7.2 is representative of intentional forest establishment by artificial regeneration or planting.

For Community Phase 7.2, determining the objectives and goals of the future stand is imperative to increase the probability of successful establishment and production of the afforested area. These decisions will ultimately determine the species to be established, preparation requirements, planting density, and post-planting operations (e.g., competitor control, future improvement cuttings and thinnings, regeneration methods, and overall stand health). Since each area targeted for afforestation may have unique or different land use histories, having a clear understanding of the soil-site conditions is essential. Some areas may necessitate a series of soil improvement actions prior to planting. These actions may include subsoiling or deep plowing to breakup plow pans and fertilizing the targeted area. An additional option is to allow the area to undergo fallowing for a predetermined period (Community Phase 7.1) to potentially increase soil organic matter content, enhance soil aggregate stability, increase soil biological activity, and improve water holding capacity and infiltration rates. Controlling competing vegetation (chemical and/or mechanical treatment) will be critical. Post-planting operations and maintenance of the stand can enhance survival, future development, and achieve goals and objectives (see Gardiner et al., 2002).

Finding the appropriate approach for a given environment necessitates close consultation with trained, experienced, and knowledgeable forestry professionals. If there is a desire to proceed with this state, it is strongly urged and advised that professional guidance be obtained and a well-designed afforestation and silvicultural plan developed in advance of any work conducted. For an exceptional review and summarization of the afforestation literature, techniques, and practices within the Southern Mississippi River Alluvium, interested parties are directed to Gardiner et al. (2002).

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This state is representative of the range of conservation actions that may be implemented and established on this ecological site. Apart from planting trees and managing for forest, one may elect to establish native herbaceous species and manage for predominantly a native grassland; a complex mixture of native grasses and forbs; or a pollinator planting whereby native forbs dominate the mix. In each of these options, it is strongly advised (possibly a programmatic requirement) that the species comprising the planting or seed mix consist of spring, summer, and fall flowering species. Depending on goals and objectives, various conservation programs and practices may be available. For additional information and assistance, please contact or visit the local NRCS Field Office.

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