Ecological dynamics
Very little exists in the literature concerning natural vegetation communities on high sodium soils east of the Mississippi River. A little more information has been documented and reported on the western counterpart of this site, which occurs within the Western Lowlands ecoregion of eastern Arkansas and southeastern Missouri. The following treatment regarding the plant communities and ecological dynamics of this site are drawn from existing literature and observations of the western counterpart.
This ecological site occurs primarily on Pleistocene-age terraces and potentially along the margins of alluvial floodplains. The site is characterized by soils that are high in exchangeable sodium. These “edaphic” effects (i.e., ecological influences from soil properties) have tremendous impacts on the local plant community. Where depths are shallow to a high sodium exchange horizon, limitations to rooting depth generally results in poor vegetation response. Communities that develop under these conditions often consist of stunted trees, low-quality woodlands, and open spots of bare ground (Heineke, 1987). An additional characteristic of this site is the occasional presence of small, shallow depressions that pond during wetter periods of the year, generally in late winter to spring. These vernal pools may contribute to habitat complexity and the occurrence of additional species into an otherwise, naturally depauperate community.
The dominant species associated with the non-ponded portions of this site is post oak with associates consisting of blackjack oak, southern red oak, honey locust, hawthorn, and winged elm (USDA-NRCS, 2016). Farther to the south, loblolly pine may occur in locations where depth to the natric subsoils are deeper. (This pattern may be more associated with Deerford soils, which is currently under review.) Structurally, the site is relatively open, which provides conditions suitable for the development of an herbaceous ground layer. Ground cover may consist of poverty oat grass, threeawns, dropseeds, and sedges. Vernal pools of this site may consist of a greater concentration of water oak and willow oak, but this has not been substantiated on this site.
Historically, fire may have been a factor or influence on this site, and a range of habitat or community types likely existed. Where trees occurred, conditions probably ranged from savanna to open woodlands. Locally, prairies likely existed in a patchwork pattern among the woodlands. This mosaic likely persisted as a “physiognomic gradient” with meadows grading to savannas and savannas grading to woodlands.
Today, various land use activities have been attempted on this site. Some areas that were once cleared and farmed are now idle. Such abandoned areas may now support a moderate cover of poor quality oaks and hickory. However, there are some areas of this site under cultivation. Those sites generally occur on the deeper soils (i.e., depths to natric subhorizons are fairly deep, greater than 24 inches). Where rooting depths to natric subsoils are shallow, yields are likely to be poor and those spots avoided (Pettry and Switzer, 1998).
A minor use on this site is reportedly pastureland and hayland, though grazing periods may be limited to shorter periods in the spring (USDA-NRCS, 2016). The more productive pastures are mainly limited to areas where the depth to natric subsoils are much greater. Limitations for pastureland and/or hayland are the same as those for cropland (i.e., seasonal wetness and high sodium content).
Woodland or forest production on this site is generally poorly suited on these soils (USDA-NRCS, 2003; USDA-NRCS, 2016). However, Deerford soils reportedly have a higher potential for loblolly pine, sweetgum, and water oak (USDA-SCS, 1978). Based on what is currently known regarding extreme saline sites to the west in Arkansas and southeast Missouri (see Heineke, 1987; and personal observations, B. Hart), a timber management state is not included for this provisional site at this time. Future inventories and investigations may dictate that timber management should be included as a management option. Those efforts may also suggest that a separate ecological site is warranted for those soils possessing greater depths to the natric subsoil.
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 Northern Natric Loess Terrace ecological site. This model is based on limited inventories, 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
Natric Flatwoods
The following treatment of the reference state is based on observations and literature review of similar soils in the Western Lowlands ecoregion in eastern Arkansas and southeast Missouri. Field investigations must be conducted to adequately and accurately describe the plant communities and ecological dynamics of this site east of Mississippi River.
The key factors influencing the plant community of this site are the soils. The high exchangeable sodium of the subsoil limits the types of plants that can tolerant these extreme conditions. Heineke (1987) compared the natural community of this site to the “…xeric, acidic, rocky blufftops of the Ozark Plateau.” The trees are stunted, twisted, and small with diameters that seldom reach 12 inches. Heineke reported an instance where trees below 12 inches had ages of 170 years, and the structure of the stand was park-like with much of the ground surface being covered by lichens.
The pre-settlement community of this ecological site may have consisted of a complex of physiognomic characteristics that included meadow or barren-like conditions, savannas, and open woodlands. Fire may have been a key disturbance factor, historically, particularly where fires extended onto this site from adjoining or nearby areas. Barren-like conditions (i.e., local bare spots) may have existed locally where depths to natric horizons were very shallow. Such “bare spots” would represent pedons of extreme root restriction.
Community 1.1
Post Oak – Blackjack Oak – Poverty Oatgrass Woodland
This community phase represents the successional stage, compositional, and structural complexity of stands supporting perceived reference conditions. Post oak is reported as the dominant species on this site; however willow oak and water oak may occur within small, shallow depressions (Klimas et al., 2012). These depressions or vernal pools are ponded only during the wetter times of the year, typically from winter to spring. Additional components and characteristics of the system include the presence of blackjack oak with an understory of hawthorn, persimmon, winged elm, and farkleberry. Ground cover may consist of blazing star, poverty oatgrass, broomsedge, woodoats, and tridens. Most notable of the ground layer is the coverage of lichens and mosses, which are interspersed by areas of bare ground.
The reference community is noted for having an open woodland profile. The subcanopy stratum is open throughout much of the community and the ground layer is thinly covered (Heineke, 1987).
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. However, soils exhibiting the core concepts of this site (i.e., a relatively shallow depth to a root restriction layer of high sodium content), are known for producing poor pasturage. Areas where natric horizons are deeper have a much better chance in pasture development and management.
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, further complicating the natural limitations of this site. Because of the limitations of this site, grazing may be limited to small intervals within the appropriate season(s). These soils have low available water capacity, low nutrients, and are prone to droughtiness. 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, haylands, and open grasslands. 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 preclude many of the commonly planted mixtures. However, there is some indication that tall fescue, common bermudagrass, and annual lespedeza have been planted on this site, but yields are reported as low (USDA-NRCS, 2006b). This site is generally considered poorly suited to not suited for this land use (USDA-NRCS, 2003; 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 fairly limited. Crops that are or have been grown include soybean and cotton but plants may be stunted and often will not reach maturity (Pettry and Switzer, 1998; USDA-SCS, 1978). Many idle woodlots today were likely cropped at some point in the past and met with disappointing results.
Community 3.1
Cropland
Soybean and cotton have been planted on this site. Poor yields may result where depths to the natric horizon is shallow.
State 4
Post Abandoned Woodland
Most, if not all, of the woodlots and local patches of woodlands occurring on this site represent this state. Former cropland and pastureland that failed to meet expectations were abandoned and are now considered “idle”. 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, small openings and a ground cover of herbaceous species provide indications of strong edaphic influences. Restoration potential of these sites back to reference conditions may be fairly high, provided the appropriate management regime is initiated and maintained. Where depth to the natric subsoil is much greater, productivity and plant composition may be very different. More work is needed to ascertain the full characteristics of this ecological site.
Community 4.1
Post – Willow – Water Oak Woodlot
This community phase represents the species characteristic of the regenerating woodlots. Post oak is often the dominant species with associates consisting of willow oak, water oak, southern red oak, hickory, and winged elm. Loblolly pine may be an additional component to the south, especially where depth to the natric subsoil is greater.
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 cultivation (State 3).
Transition T2A
State 2 to 3
Actions include removal of vegetation or pasturage; herbicide treatment of residual plants; and preparation for crop establishment.
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.
Transition 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 natural succession 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 cultivation (State 3).
