Integrating Ecological Site Descriptions with Soil Morphology to Optimize Forest Management: Three Missouri Case Studies

Academics and University Extension personnel have experience with soil mapping and providing soil suitability interpretations; however, a more efficient information conveyance to land custodians is desired to support informative land management applications. In the USA each state, in concert with the United States Department of Agriculture, has embarked on developing an online format linking soil survey with ecological site descriptions to provide information for forest and rangeland management to encourage soil protection - health and optimizing ecological services on individual land parcels. In this Missouri-based manuscript, we discuss three cases where soils and their associated ecological site descriptions provide land custodians information concerning their logical reference state vegetation community and detail land management decisions that transform the reference vegetation community to a different vegetation community. With each case, landscapes and their associated vegetations communities are potentially partitioned by soil, physiography, hydrology, and other attributes.


Introduction
Alfisols are a soil order in USA "Keys of Soil Taxonomy" [1]. Alfisols are typically developed under mixed forests in temperate climates that maintain a low to moderate level of soil organic matter, a neutral to acidic pH and have a moderate degree of base saturation. One requirement of Alfisols is the presence of an argillic horizon, coupled with the requirement of having a base saturation greater than 35% in the argillic horizon control section [1]. In Missouri, Alfisols typically have aquic and udic moisture regimes and support deciduous forest vegetation [2]. Ultisols are a soil order in USA "Keys of Soil Taxonomy" that are similar to Alfisols with the exception that Ultisols have less than 35% base saturation in the control section [1].
The USDA-NRCS has developed the National Soils Information System based on a national soil survey composed of establishing soil characteristics using observations along soil delineation boundaries and determining map unit compositions Integrating Ecological Site Descriptions with Soil Morphology to Optimize Forest Management… DOI: http://dx.doi.org /10.5772/intechopen.97251 Ecological site descriptions are not mapping units, rather they are taxonomic units. However, ecological site descriptions of an appropriate areal extent may be used as mapping units when the sites are highly patterned because of site topography, soil distribution, geology, and other attributes. The repeatable distribution of ecological sites provides for their useful application to manage land under the influence of livestock grazing, wildlife habitat, recreation, rural or urban development, forestry, and a multitude of other land uses. In general, we accept the definition proposed by Bestelmeyer et al. [13] and Briske et al. [14] to define an ecological site as landscape units that have similar characteristics of soil, topography, geological formations, and climate regimes that differ because of (i) the production and plant species composition under the disturbance of reference conditions associated with soil properties, the natural dynamics of vegetation and the ecosystem services provided, and (ii) the responses to management, processes of degradation, and restoration.
State and Transition Models attempt to explain how ecosystems transition from one state to another state. A state is a series of plant communities associated with specific soil properties that produce persistent attributes over time with structural and functional ecosystem characteristics [15]. The reference state is a state that provides the largest range of potential environmental services and typically is the "ideal" state. At its essence, researchers aim to understand how ecosystems function and respond to management or natural influences. Ecological resilience is the capacity to absorb and/or reorganize after a disturbance yet maintaining the site's structural integrity [15]. Thresholds are key biotic and abiotic factors and modified ecosystem functions that alter the ecosystem structure beyond the limits of ecological resilience resulting in a transition to a different state or limits recovery. Triggers are events, factors, processes and/or drivers that initiate a transition from one state to another.
The objectives of this project are to document the importance of combining soil survey information with ecological site descriptions to show relationships (i) between soil genesis-soil morphology with their resident plant communities, and (ii) and the actions of land management to alter the resident plant communities to a different plant community.

Study areas
The study areas are all located in southeastern Missouri, USA. The study area containing the Knobtop, Taumsauk and Irondale Ultisol pedons is located at Taumsauk State Park and was selected because of its variable pedon depths and the presence of loess over igneous residuum/colluvium. The Knobtop (Fine-silty, mixed, active, mesic Aquic Hapludults) pedon is a moderately deep, moderately well-drained soil formed in loess overlying Precambrian rhyolite residuum. The pedon is located on a summit position having a 1 to 2 percent slope. The Irondale (Loamy-skeletal, mixed, active, mesic Typic Hapludults) pedon is moderately deep, well-drained, and moderately permeable soil formed in rhyolite residuum on a steep 35% slope supporting an oak forest. The Taumsauk (Loamy-skeletal, mixed, active, mesic Lithic Hapludults) pedon is a shallow, somewhat excessively-drained, moderately permeable soil formed in rhyolite colluvium. The Taumsauk pedon is located on a 10% convex slope and exhibits a mountain glade area.
The Caneyville and Hildebrecht pedons are in Sam A Baker State Park and were selected because the pedons were formed in loess over limestone residuum, Environmental Management which is a very common occurrence across east-central Missouri. The Caneyville (Fine, mixed, active, mesic Typic Hapludalfs) Alfisol pedon is a moderately deep, well-drained soil formed in a thin silty mantle overlying fine-textured limestone residuum. The Hildebrecht (Fine-silty, mixed, active, mesic Oxyaquic Fragiudalfs) Alfisol pedon is a very deep, moderately well-drained soil on a side slope. The pedon is formed in loess over weathered dolomitic residuum. Permeability is moderate above the fragipan and slow or very slow in the fragipan.
The study area containing the Amagon (Fine-silty, mixed, active, thermic Typic Endoaqualfs) and Calhoun (Fine-silty, mixed, active, thermic Typic Glossaqualfs) pedons are located in the Mingo National Wildlife Refuge. This study area was selected because these poorly-drained pedons were formed in alluvium, which is representative of the Mississippi River Embayment. The Amagon pedon is a very deep, poorly-drained, slowly permeable Alfisol that formed in loamy alluvium. The Calhoun pedon is a poorly-drained, slowly permeable Alfisol formed from loess-like material on a Pleistocene-age terrace.
The Knobtop, Taumsauk and Irondale study area and the Caneyville and Hildebrecht study area have a continental humid climate with winter having dry and cold air masses and summer having moist, warm air masses producing abundant rainfall events. The average annual precipitation 112 cm, whereas the average annual temperature is about 13°C [16]. The Amagon and Calhoun study area has a continental humid climate with an average rainfall of 126 cm. Mean winter temperatures are 4°C and mean summer temperature of 26°C, whereas the mean annual temperature is 13°C [17]. The The Knobtop, Taumsauk and Irondale study area and the Caneyville and Hildebrecht study area does not experience flooding, whereas the Amagon and Calhoun study area annually experiences either flooding or seasonal water saturation.

Methodology
Pedons were located, described, and sampled according to Soil Survey Division Staff [18] in undisturbed forest settings using excavated pits. Samples were ovendried, lightly crushed, and sieved to remove materials larger than two mm. Soil pH using equal volumes of soil and water, the NH 4 -acetate (pH 7.0) extraction of exchangeable bases, the total acidity by slow titration to pH 8.2, and the soil organic matter content (SOM) by loss on ignition were performed using standard methods [19]. The particle size distribution (mechanical analysis) was determined by Na-saturation of the exchange complex, dispersion in Na 2 CO 3 (pH 9.0) and centrifuge fractionation to remove clay and wet sieving of the silt and sand separates [19].
The ecological site descriptions were obtained using the Ecosystem Dynamics Interpretive Tool (EDIT), which is an online information system for the sharing of ecological site descriptions [20] or ([https://edit.jornada.nmsu.edu/], verified February 2021).

Knobtop Irondale Taumsauk Ultisol Assemblage
The Knobtop, Irondale and Taumsauk soils are Ultisols having fine silty or loamy-skeletal textures and exhibiting A-E-Bt-rhyolite rock horizon sequences. The Knobtop pedon resides on a summit position developed in a moderately thick loess mantle overlying rhyolitic residuum, whereas the Irondale and Taumsauk pedons occupy side and convex (shoulder) slope positions, respectively. The Irondale and Taumsauk pedons exhibit thin and very thin loess mantles overlying rhyolite colluvium, features attributed to erosion and mass-wasting during and subsequent to loess deposition.
The Knobtop (Aquic Hapludult), Taumsauk (Lithic Hapludult) and Irondale (Typic Hapludult) pedons reside in MLRA 116 in the St. Francois Knobs and Basins region. The Knobtop pedon exhibited a silt loam texture in the ochric epipedon and silty clay loam texture in the majority of the argillic horizon ( Table 1). The Taumsauk pedon exhibited a very cobbly silt loam ochric epipedon (A horizon) and very cobbly silt loam (E horizon) transitioning to a very cobbly silty clay loam within the comparatively shallow-to-bedrock argillic horizon. Soil pH in the Knobtop and Taumsauk pedons are extremely acid, with a corresponding base saturation much less than 35% (  a very acidic reaction, with a relatively greater base saturation; however, the base saturation remains less than 35% as required for the Ultisol order. The soil organic matter content is greatest in the A horizons and declines with increasing soil depth. Given the shallowness of these pedons, especially for the Taumsauk pedon, seasonal dryness during the summer and fall months is presumed to be a limiting factor for tree growth. The extreme soil acidity contributes to the reduced tree growth and limits the vegetational diversity. For the Knobtop-Irondale-Taumsauk Ultisol assemblage, the corresponding provisional ecological site descriptions are (i) Dry Igneous Upland Woodland (F116CY003MO) having the Knobtop and Irondale soil series, (ii) the Dry Igneous Exposed Backslope Woodland (F116CY011MO) having the Irondale soil series, and (iii) the Shallow Igneous Knob Glade (R116CY006MO) having the Taumsauk soil series. For the Dry Igneous Exposed Backslope Woodland the dominant vegetation is post oak (Quercus stellate), black oak (Quercus velutina) with scattered blackjack oak (Quercus marilandica), northern red oak (Quercus rubra) and a ground flora of native grasses and shrubs (fragrant sumac (Rhus aromatica) and little bluestem (Schizachyrium scorparium)). For the Dry Igneous Upland Woodland, the vegetational community is similar, with exceptions including a slightly greater abundance of northern red oak (Quercus rubra) and a greater abundance of the herbaceous species Danthonia spicata. The Shallow Igneous Knob Glade has a few species of blackjack oak (Quercus marilandica) and the herbaceous species Schizachyrium scorparium and Croton michauxil var. ellipticus. Canopy closure varies with aspect and soil depth, ranging from 30 to 50% on exposed positions and shallower soil depths to 50-80% on protected positions and deeper soil depths. Fire, including controlled burning, has been present in these vegetational communities, reducing litter accumulation, stimulating grasses and forbs, and reducing the encroachment of woody species.
The Dry Igneous Upland Woodland has post oak (Quercus stellate) and northern red oak (Quercus rubra) as the dominant tree species in the reference state, with a fire-free interval of 10-15 years witnessing the encroachment of eastern red cedar (Juniperus virginiana). The reference state is in quasi-equilibrium with (i) the fire excluded mixed oak woodland state and the (ii) fire excluded and logged mixed oak woodland state based on the contrasting practices of long-term fire suppression and the opposing practice of forest stand improvement using prescribed burning with and without tree species removal. The Dry Igneous Exposed Backslope Woodland reference site and transition sites are similar to that of the Dry Igneous Upland Woodland, with differences attributed to subtle species compositions. The Shallow Igneous Knob Glade has a blackjack oak (Quercus marilandica) tree composition with little bluestem (Schizachyrium scoparium) and lichens with and associated reference state having eastern redcedar. Fire suppression transitions to a state with the addition of winged elm (Ulmus alata). The soil surface cover is variable, but typical estimates are tree basal cover (1%), shrub/vine/liana basal cover (1%), grass and grasslike basal cover (1%), forb basal cover (1%), non-vascular cover (5%), litter (30-50%) and surface fragments (10%).

Caneyville and Hildebrecht Alfisol Assemblage
The Caneyville and Hildebrecht soils are Alfisols having fine and fine-silty textures and exhibiting A-E-Bt and A-E-Bt-2Btx-3Bt horizon sequences, respectively ( Table 3). The consensus of soil scientists who mapped these soils is that the Caneyville series developed in loess, whereas the Hildebrecht series developed in Peoria loess overlying a previous bisequal soil derived from older loess developed on limestone residuum.

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The Caneyville (Typic Hapludalf) pedon has sandy loam and silt loam textures in the ochric epipedon and silty clay loam in most of the argillic horizon. The pH is neutral to slightly acidic in the near surface horizons and strongly acid in the lower argillic horizons, with exchangeable Ca showing a gradual concentration reduction on transition to the deeper horizons ( Table 4). The Hildebrecht (Oxyaquic Fragiudalf) pedon shows a silt loam texture in the eluvial horizons and a silty clay loam texture in the illuvial horizons. The fragipan has a loam texture which abruptly transitions to clay in the 3Bt3 horizon. The eluvial and argillic horizons appear to be developed in Peoria Loess, whereas the fragipan and 3Bt3 horizons are apparently developed in older Roxana Loess overlying limestone residuum, thus the Hildebrecht pedon appears to be a bisequal soil. The soil organic matter concentrations are greatest in the A horizons and decline upon soil profile transition.

Amagon and Calhoun Alfisol Assemblage
The Amagon (Typic Endoaqualf) pedon and the Calhoun (Typic Glossaqualf) pedon possess A-E-Btg horizon sequences showing extensive redoximorphic features supportive of their poor-drained status ( Table 5). These pedons have a relatively high cation exchange capacity, reflecting the abundance of smectite in the clay separate (X-ray diffraction data not presented). The near surface horizons have  Environmental Management a very strongly acid or strongly acid reaction, transitioning to a slightly alkaline to neutral reactions in the argillic horizons ( Table 6). The Amagon pedon also exhibits an elevated exchangeable sodium percentage in the argillic horizon.