Ecological dynamics
This ecological site is distributed across broad expanses of level to nearly level flats on Early Wisconsin Terraces (Klimas et al., 2012). A key characteristic of this site is the propensity of these poorly drained soils to perch water during wetter times of the year. Poor surface runoff and slow permeability contributes to saturated conditions from winter through spring in most years. Ironically, this extreme wet condition through the first part of the year is reversed by mid- to late summer when evapotranspiration essentially removes moisture above the soils’ perching layer, which is either a true fragipan or what some refer to as a claypan. This leads to very droughty conditions during summer and fall. The alternating wet – dry pattern of this site characteristically occurs in other “flatwoods” communities in the eastern United States (see Taft et al., 1995; Fralish et al., 1999). This moisture regime is often referred to as “hydroxeric”. It’s important to note that this site is generally above the modern floodplains of larger streams and rivers of the Western Lowlands and receives very little overland flow (NatureServe, 2009). Exceptions occur where this site borders small tributaries or drains and especially when beaver activity plugs such watercourses (T. Foti, personal communication). Interspersed across the broad flats of this site are surface irregularities that include occasional, subtle mounds or microhighs and distinct, shallow depressions. These microreliefs contribute to species and site diversity, overall.
Because of the moisture regime and surface complexities, plant communities of this site are highly variable with some areas consisting predominantly of willow oak flats and others post oak flats. Species characteristic of uplands and lowlands are often seen co-occurring within a small area (e.g., post oak, an upland species beside overcup oak, typically a wetland species). Areas that remain wetter for longer periods, such as shallow depressions, may support a greater abundance of pin oak and overcup oak; Klimas et al. (2012) lists Nuttall oak as an additional species occurring in vernal pools. Conversely, areas that tend to dry more quickly may support a preponderance of post oak and other upland species. One postulate concerning the co-occurrence of species with dramatically different moisture tolerances hinges on cyclical weather patterns of dry and wet years (LANDFIRE, 2008).
Historically, fire was probably a key factor or influence on this site. Low-intensity fires would occur when adjacent systems burned, and since some of the tree species on this site are fire sensitive, fire-caused root death likely contributed to an open canopy. Stand replacement fires, although rare, would have occurred during extreme, prolonged droughts (LANDFIRE, 2008). These key disturbance factors would have contributed to a range of habitat or community types. Where trees occurred, conditions probably ranged from savanna to open flatwoods. Locally, meadows or prairies existed in a patchwork pattern among the woodlands and/or savannas. This mosaic likely persisted as a “physiognomic gradient” with meadows grading to savannas and savannas grading to woodland – and vice versa (T. Foti, personal communication).
The predominant land use activity on this site today is agriculture production with principal crops being soybean, rice, cotton, and grain sorghum (USDA-NRCS, 2006b). Depending on crop type, manipulation and management of surface water and drainage capabilities of a given site is generally implemented. A minor use on this site is reportedly pastureland or hayland with principal forage of bermudagrass, bahiagrass, and tall fescue. This site has some limitations for forest production, mainly due to seasonal wetness but also dryness during summer and fall. (Forest production is a very minor use on this site as the vast majority of the site’s distribution is cropland. Therefore, forest or timber management as a state is not represented in the accompanied State and Transition Model.)
Following this narrative, a “provisional” state and transition model is provided that includes the “perceived” reference state and several alternative (or altered) vegetation states that have been observed and/or projected for the Western Wet Loess Terrace ecological site. This model is based on limited reconnaissance, literature, expert knowledge, and interpretations. Plant communities will differ across MLRA 134 due to natural variability in climate, soils, and physiography. Depending on objectives, the reference plant community may not necessarily be the management goal.
The environmental and biological characteristics of this site are complex and dynamic. As such, the following diagram suggests pathways that the vegetation on this site might take, given that the modal concepts of climate and soils are met within an area of interest. Specific locations with unique soils and disturbance histories may have alternate pathways that are not represented in the model. This information is intended to show the possibilities within a given set of circumstances and represents the initial steps toward developing a defensible description and model. The model and associated information are subject to change as knowledge increases and new information is garnered. This is an iterative process. Most importantly, local and/or state professional guidance should always be sought before pursuing a treatment scenario.
State 1
Wet Hydroxeric Flatwoods
Exemplary examples of the full range of plant communities and ecological processes that were once commonplace on this ecological site no longer exist. Vestiges of this once vast system are primarily relegated to abandoned woodlots and narrow, roadway corridors that now hold the only remaining example of native prairie vegetation that was once part of the greater ecological system. However, there is one example where the soils of this site occur in complex with other ecological sites forming a mosaic of wet hardwood flats (this ecological site), loblolly pine flats, and alkali flatwoods within a relatively confined area. It is from this example and remaining remnants, mostly abandoned woodlots, that we draw a greater understanding of the “perceived” reference conditions for this ecological site.
Klimas et al. (2012) identified this site as “hardwood flats (wet phase).” The saturated, poorly drained soils during winter and spring supports conditions suitable for more lowland species such as willow oak, overcup, and pin oak – the latter two more typical of vernal pools. The drying of the soils by summer create conditions suitable for more upland species, the principal species of which is delta post oak and/or post oak. To the south, loblolly pine is locally a dominant species. However, loblolly pine has a fairly restricted range in the Western Lowlands and is not a characteristic species through the northern portions of this ecological site (T. Foti, personal communication).
Embedded among the woodlands of this site were prairies and savannas, some of which were likely extensive. Vegetation of the open areas would have been quite similar to that of the Grand Prairie to the south. It is generally held that areas of prairie extended or “fingered” northward from the Grand Prairie province well into the Western Lowlands (T. Foti, personal communication).
Two community phases are recognized for representing the reference state of this ecological site: 1) the open structure of the flatwoods and 2) prairie and savanna.
Of the utmost concern, this site has incurred tremendous alteration to drainage. Any attempt to reestablish perceived reference conditions of a stand or a local site must first restore the natural hydrology of that site, which may entail removing drainage structures. If not, management may improve stand structure and even composition to a degree, but the site, overall, will remain in an altered state relative to the reference state. Retaining drainage structures (either pulling excessive water off or retaining water for rice) will directly influence the types of vegetation that colonize the site, which may be entirely different than reference conditions.
Community 1.1
Delta Post – Willow – Water Oak Flatwoods
This community phase represents the successional stage, compositional, and structural complexity of stands supporting perceived reference conditions. For the wet flatwoods community, this phase represents late development with and without frequent, low-intensity fire. Where the recurrence of fire is more frequent, the canopy is more open, taking on an open woodland structural characteristic. Under this fire regime, herbaceous cover is anticipated to be quite dense with the possible exception of depressions that remain wet for longer periods. Where fire is very infrequent, canopy cover may approach closure but the overall structure of the understory generally remains somewhat open. This is generally a common structural feature of flatwoods systems in other areas of the U.S. (Taft et al., 1995; Fralish et al., 1999).
Composition of this community is quite variable ranging from delta post oak (or post oak) flatwoods to willow oak flatwoods (Klimas et al., 2012). Associates of these stands may include water oak, swamp chestnut oak, sweetgum, hickory, black gum, elm, red maple, green ash, sassafras, and persimmon. Wetter locations such as depressions may support higher abundances of overcup oak, pin oak, Nuttall oak, buttonbush, and water elm. The understory is generally open and is often occupied by smaller, canopy species and possumhaw. Vines and lianas are represented by roundleaf greenbrier, climbing dogbane, and muscadine. Ground cover may be sparse where canopies are more closed. Herbaceous species associated with this site includes several sedges, sweet wood reed, redtop panic grass, St. Andrews cross, Virginia dayflower, thoroughwort, flattop goldentop, ironweed, large areas of Sphagnum moss (Heineke, 1987).
Community 1.2
Prairie/Savanna
This community phase represents another aspect of the historic community on this site, prairie and savanna. Prairies of the Grand Prairie province extended into and through portions of the Western Lowlands (T. Foti, personal communication). Periodic fires on a 1 to 3 year return interval would have maintained their presence and persistence (LANDFIRE, 2008). This community type within the Western Lowlands was reported and somewhat described by early naturalists traveling through the region (see Heineke, 1987) and from naturalists as late as one century ago (e.g., Harper, 1914 and 1917).
Vegetation of the prairies and savannas are thought to have been similar to that of the Grand Prairie (T. Foti, personal communication). Harper (1917) mentioned this similarity while examining a small prairie in Craighead County, Arkansas. He mentioned the site being bordered by a scattering of pin oak. Species anticipated to occur across the prairies of this site include switchgrass, big bluestem, Indian grass, little bluestem, prairie blazing star, pinkscale blazing star, wild indigo, compass plant, meadow evening primrose, wild quinine, wooly ragwort, hoarypea, and Baldwin’s ironweed (Heineke, 1987; NatureServe, 2015) among many additional taxa.
Pathway 1.1A
Community 1.1 to 1.2
This pathway represents a major stand-scale disturbance such as extensive, prolonged drought, wind, catastrophic ice, and/or stand replacement fire. Such catastrophic events would then be followed by low-intensity surface fires on a frequent return interval, which would support transition to prairie and/or savanna conditions.
Pathway 1.2A
Community 1.2 to 1.1
This pathway represents a return to an open woodland or flatwoods structural characteristic. Processes leading to woodland conditions is a relaxation of fire or fire occurring on a much longer return interval. Disturbance occurs at the gap-scale (i.e., less than 1 acre).
State 2
Pasture
This state is representative of sites that have been converted to and maintained in pasture and forage cropland, typically a grass – legume mixture. For pastureland, planning or prescribing the intensity, frequency, timing, and duration of grazing can help maintain desirable forage mixtures at sufficient density and vigor (USDA-NRCS, 2010; Green et al., 2006). Overgrazed pastures can lead to soil compaction and numerous bare spots, which may then become focal points of colonization by undesirable plants or weeds. Soils exhibiting the core concepts of this site have a pronounced period of wetness followed by droughty conditions. Limitations may pertain mainly to periods of extreme wetness.
Planning or prescribing the intensity, frequency, timing, and duration of grazing can help maintain desirable forage mixtures at sufficient density and vigor (USDA-NRCS, 2010; Green et al., 2006). Because of the limitations of this site, grazing may be limited to small intervals within the appropriate season(s). It is strongly advised that consultation with State Grazing Land Specialists and District Conservationists at local NRCS Service Centers be sought when assistance is needed in developing management recommendations or prescribed grazing practices on this site.
Community 2.1
Select Forage/Species Mixture
This community phase represents commonly planted forage species on pasturelands and haylands. The suite of plants established on any given site may vary considerably depending upon purpose, management goals, usage, and soils. The limitations of this site may preclude some of the commonly planted mixtures. However, there is some indication that tall fescue, common bermudagrass, bahiagrass, and annual lespedeza are adapted to this site (USDA-NRCS, 2006b).
Should active management (and grazing) of the pastureland be halted, this phase will transition to “old field” conditions, which is the transitional period between a predominantly open, herbaceous field and the brushy stage of a newly initiated stand of trees.
State 3
Agriculture Production
Agriculture production on this site is somewhat limited due to seasonal wetness. However, the vast majority of the acreage in this ecological site is in agriculture production. Where idle woodlots occur today, those sites were very likely cropped at some point in the past.
Community 3.1
Cropland
Soybean, rice, cotton, and grain sorghum (USDA-NRCS, 2006b).
State 4
Post Abandoned Woodland
Most, if not all, of the woodlots and local patches of woodlands occurring on this site represent this state. These stands still support some of the components that characterizes the community. The structure of these stands are typically denser than a late development, fire-influenced stand. However, the co-occurrence of upland and lowland taxa and a moderately open understory provide indications of hydroxeric influences. Restoration potential of these sites back to reference conditions is possible, provided that the appropriate management regime is initiated and maintained. Before this can happen, the natural hydrology of the area of interest must first be restored, which may entail removing drainage structures. If not, management may improve stand structure and even composition to a degree, but the site, overall, will remain in an altered state relative to the reference state.
Community 4.1
Delta Post – Willow – Water Oak Dense Woodlot
This community phase represents the species characteristic of the regenerating woodlots. Delta post oak is often the dominant species with associates consisting of willow oak, water oak, southern red oak, hickory, winged elm, green ash, and an occasional cherrybark oak.
Transition T1A
State 1 to 2
This pathway represents an attempt to convert the woodland community to pasture or forage production. Actions include clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants (State 2).
Transition T1B
State 1 to 3
Actions include mechanical removal of vegetation and stumps; herbicide treatment of residual plants; and preparation for planting. May include the installation of drainage control structures (State 3).
Transition T2A
State 2 to 3
Actions include removal of vegetation or pasturage; herbicide treatment of residual plants; and preparation for planting.
Transition T2B
State 2 to 4
Abandonment of grassland/pastureland management and allowing natural succession to proceed beyond the old field stage to canopy development of the young woodland.
Restoration pathway R3A
State 3 to 2
Seedbed preparation and establishment of desired forage/grassland mixture.
Transition T3A
State 3 to 4
Abandonment of cropland management and allowing natural succession to proceed to canopy development of the young woodland.
Restoration pathway R4A
State 4 to 1
This pathway represents restoration back to perceived reference conditions. The period required for this transition to take place likely varies by location and is dependent upon local site conditions. In some cases, a return to the reference state may not be possible without considerable management effort. That effort may involve exotic species control, restoration of the natural hydrologic regime of a given locality, and the reestablishment of components considered characteristic of the reference state.
Transition T4A
State 4 to 2
This pathway represents an attempt to convert the woodland community to pasture or forage production. Actions include clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants (State 2).
Transition T4B
State 4 to 3
Actions include mechanical removal of vegetation and stumps; herbicide treatment of residual plants; and preparation for planting (State 3).
