Ecological dynamics
Information contained in this section was developed using historical data, professional experience, field reviews, and scientific studies. The information presented is representative of very complex vegetation communities. Key indicator plants, animals and ecological processes are described to help inform land management decisions. Plant communities will differ across the MLRA because of the naturally occurring variability in weather, soils, and aspect. The Reference Plant Community is not necessarily the management goal. The species lists are representative and are not botanical descriptions of all species occurring, or potentially occurring, on this site. They are not intended to cover every situation or the full range of conditions, species, and responses for the site.
The reference plant community is an open woodland dominated by an overstory of post oak and black oak, with and occasional pin oak, elm and hickory. The canopy is moderately tall (55 to 70 feet) but less dense (30 to 60 percent closure) and less structurally diverse than adjacent Loess Upland Woodlands or Till Backslope Woodlands and Forests. Increased light from an open canopy causes a diversity of woodland ground flora species to flourish, especially prairie grasses. The claypan soil subsoil perches water in the spring and affects rooting depth of this ecological site limiting the growth of trees and supporting an abundance of native grasses and forbs in the understory. Seasonal wetness allows an abundance of sedges and wild ryes to occur in the understory. Woodlands are distinguished from forest, by their relatively open understory, and the presence of sun-loving ground flora species. Characteristic plants in the ground flora can be used to gauge the restoration potential of a stand along with remnant open-grown old-age trees, and tree height growth.
Because of their proximity to prairies, fire played a significant role in the maintenance of these systems. It is likely that these ecological sites burned at least once every 3 to 5 years. These periodic fires kept woodlands open, removed the litter, and stimulated the growth and flowering of the grasses and forbs. During fire free intervals, woody understory species increased and the herbaceous understory diminished. The return of fire would open the woodlands up again and stimulate the abundant ground flora.
Claypan Summit Woodlands were also subjected to occasional disturbances from wind and ice, as well as grazing by native large herbivores. Wind and ice would have periodically opened the canopy up by knocking over trees or breaking substantial branches off canopy trees. Grazing by large native herbivores would have effectively kept understory conditions more open, creating conditions more favorable to oak reproduction and woodland ground flora species.
Today, most of these ecological sites have been cleared and converted to pasture and cropland. Remaining woodland ecological sites have a younger (50 to 80 years) canopy layer whose species composition and quality has been altered by timber harvesting practices. In the long term absence of fire, woody species, especially hickory and sugar maple, encroach into these woodlands. Once established, these woody plants can quickly fill the existing understory increasing shade levels with a greatly diminished ground flora. Removal of the younger understory and the application of prescribed fire have proven to be effective restoration means.
Uncontrolled domestic grazing has also impacted these communities, further diminishing the diversity of native plants and introducing species that are tolerant of grazing, such as buckbrush, gooseberry, and Virginia creeper. Grazed sites also have a more open understory. In addition, soil compaction and soil erosion can be a problem and lower productivity.
These ecological sites are not very productive. Oak regeneration is typically problematic. Eastern hop hornbeam and hickories are often dominant competitors in the understory. Maintenance of the oak component will require disturbances that will encourage more sun adapted species and reduce shading effects. Some thinning of the dense stands and periodic fire will be needed to maintain the ground flora diversity and open stand structure.
A State and Transition Diagram follows. Detailed descriptions of each state, transition, plant community, and pathway follow the model. This model is based on available experimental research, field observations, professional consensus, and interpretations. It may change as knowledge increases.
State 1
Reference
These open woodland communities were strongly influenced by fire and seasonal soil wetness. Herbivory by native (now expatriated) ungulates also played a role. Consequently, fire-tolerant post and black oaks over a ground flora of tallgrass prairie grasses, sedges and wildflowers made up the claypan woodland. There are two phases associated with this Reference State.
Community 1.1
Post Oak-Black Oak/Wild Plum/Switchgrass - Sedge
The overstory in this phase is dominated by post oak and black oak, with scattered hickories. This open woodland community typically has a two-tiered structure, with canopy height of 35 to 50 feet and 30 to 60 percent closure. The abundant herbaceous layer is dominated by switchgrass, little bluestem, big bluestem and Indian grass. Fire frequency was every 1 to 3 years. This continued fire and natural native grazing would have maintained the more open canopy and profusion of ground flora species.
Forest overstory. The Forest Overstory Species list is based on commonly occurring species listed in Nelson (2010).
Forest understory. The Forest Understory Species list is based on commonly occurring species listed in Nelson (2010).
Community 1.2
Post Oak - Black Oak/Hickory/Switchgrass - Sedge
The overstory in this phase is dominated by post oak and black oak, with scattered hickories. This brushy woodland community typically has a three-tiered structure, with 50 to 80 percent closure. It is characterized by a thick understory of oak saplings, and shrubs. The herbaceous layer is dominated by prairie grasses and sedges. Fire-free intervals ranged from 5 to 10 years.
State 2
Fire Suppressed Woodland
Most current areas of Claypan Woodlands have experienced fire exclusion for decades. In the absence of fire, ongoing recruitment of trees into the canopy develops a closed canopy, shading out the herbaceous ground flora. This results in the formation of Post Oak – Black Oak – Black Hickory / Oak – Hickory Saplings / Goldenrod woodland. Black oak and midstory species increase. Herbaceous cover and diversity greatly diminishes, leaf litter builds up, and more shade-tolerant woodland species persist, such as elm-leaved goldenrod, panic grass and spreading aster. The understory also develops with oak and hickory saplings along with sassafras and black cherry. Transition to cool season grasslands (State 3) or intensive cropland (State 4) is very common.
Community 2.1
Black Oak - Post Oak - Hickory/Oak Saplings - Elm/Goldenrod
Oak and hickory species are increasing due to fire suppression. Displacement of grasses and forbs is occurring due to shading and competition from the increased densities of oak and hickory saplings. Canopy cover ranges from 70 to 90 percent. Most stands are 50 to 80 years of age.
State 3
Cool Season Grassland
Conversion of other states to non-native cool season species such as tall fescue and red clover has been common in the Missouri Central Claypan area. Occasionally, these pastures will have scattered post and pin oaks. Long term uncontrolled grazing can cause significant soil erosion and compaction. A return to the Reference State may be impossible, requiring a very long term series of management options.
Community 3.1
Tall Fescue - Orchard Grass - Red Clover
This phase is well managed grassland, composed of non-native cool season grasses and legumes. Grazing and haying is occurring. The effects of long-term liming on soil pH, and calcium and magnesium content, is most evident in this phase. Studies show that these soils have higher pH and higher base status in soil horizons as much as two feet below the surface, relative to a poorly managed grassland and to woodland communities (where liming is not practiced).
State 4
Cropland
This is the dominant State that exists currently with intensive cropping of corn, soybeans, and wheat occurring. Some conversion to cool season grassland occurs for a limited period of time before transitioning back to cropland. Limited acres are sometimes converted to native warm season grassland.
Community 4.1
Corn, Soybean, Wheat
This phase has intensive cropping of corn, soybeans, and wheat. Tillage operations generally leave little residue on the surface over winter. Surface drainage has usually been altered.
State 5
Native Warm Season Grassland
Conversion from the Cool Season Grassland (State 3) or the Cropland (State 4) to this State is increasing due to renewed interest in warm season grasses as a supplement to cool season grazing system or as a native restoration activity.
Community 5.1
Big Bluestem - Switchgrass - Indiangrass
This phase is dominated by planted native warm season grasses. Some plantings are the result of participating in government programs.
