Ecological dynamics
Wet Floodplain ecological sites occupy low landscape positions in the floodplain associated with former meander scars, tributary stream channels, and backwater lowlands between natural levees. These sites exist because of their association with low, wet areas with poorly drained, heavy textured soils. These conditions along with periodic fire have a strong influence on excluding trees. Wet Floodplains are dominated by a dense cover of wetland species, including prairie cord grass, sedges, and wet tolerant forbs. Slightly higher areas within or at the edge of the prairie support widely scattered elm, bur oak, pin oak, shellbark hickory, and willow.
Prior to levee development and channeling, these areas were regularly flooded by typically slow-moving backwater floods. Some further inundation and ponding occurred through groundwater movement. Unaltered sites usually were flooded at least three months of the year. In addition to flooding, periodic fire also played a role in keeping woody species at bay. Fire during dry periods removed the dense mat of leaf litter creating opportunities for plants less aggressive than the grasses and sedges. In the long term, siltation slowly filled these depressions, altering flood duration and causing a shift toward floodplain forest communities.
Today most of these ecological sites have been drained and farmed. However, because of their site conditions, during wet years, they act as ephemeral farmed wetlands in the agricultural landscape. While their flood regime usually has been altered, their position and soil properties still make them good candidates for wet prairie development management. Left unfarmed, these sites can quickly develop into naturally wet communities.
The state and transition model is provided to diagram the complex interactions briefly discussed here. The model includes states, plant communities, transitions, and restoration pathways detailing what experts have gathered from available experimental research, field observations, professional consensus, and interpretations. There may be other states or plant communities, with additional transitions and restoration pathways, not shown in the model, as well as noticeable variations within those illustrated.
The state and transition model consists of six states and seven community phases. These states and community phases interact based on the timing, intensity, and frequency of prescribe burning and prescribed grazing, flooding events, introduction of invasive species, and tillage practices. The Reference State (1) is typically burned every 1 to 3 years. Fire removes dead plant litter and provides room for a lush growth of prairie vegetation. Fires and intense flooding events also keep woody species from invading the rangeland. The Woody Invaded State (2) is characterized by a fire frequency and return interval greater than 20 years and a canopy cover percent between 40 and 60 percent. The Prior-Tilled State (3) consists of sites that were allowed to regenerate through natural revegetation or artificially reseeded after tillage practices have ceased. The Invasive Herbaceous State (4) is characterized by invasive, non-native grasses and forbs. The Cropland State (5) consists of land converted to agricultural cropland and dominated by row crops. The Pastureland State (6) is characterized by seeded grasses, usually cool season, that receive fertilizer and irrigation inputs to maintain the pasture, often used for grazing.
State 1
Reference
The Reference State is dominated by water tolerant vegetation such as wet prairies or sedge meadows that are not connected to groundwater (not seepage communities or fens). It experiences full horizon saturation (endosaturation), at least briefly throughout the growing season. Sites usually are flooded at least three months of the year. Long duration flooding regimes are common during some years.
Within this state are two plant community phases that can occur and will transition back and forth depending on fire return intervals and flooding events.
Characteristics and indicators. An introduction and/or increase of woody plants can occur in the Reference State and initiates the transition to the Woody Invaded State. With the lengthening of fire return interval, lack of fire intensity, and lack of significant flooding events, there is a greater chance of woody species to establish and increase. Within the Reference State, the woody vegetation will generally be less than 15 percent canopy cover per acre. An introduction of seed from introduced, invasive or noxious plants can occur in the Reference State and is the starting point for transition to the Pastureland and/or Invasive Herbaceous State. If introduced, invasive, or noxious plants are present, they should not exceed those percentages shown in the plant communities identified in the Pastureland State and Invasive Herbaceous State. Tillage has not been a disturbance in the Reference State.
Resilience management. The Reference State is maintained through fire, flooding, and management. Longer fire return intervals and a lack of flooding events will allow woody species to increase. When fire return intervals shorten, or when there is significant flooding, these woody species will decrease or be eliminated. Management will include strategies to prevent non-native seed introduction (woody or herbaceous) and scouting with targeted control methods if initial establishment occurs.
Community 1.1
Reference
This community is characterized by wet-tolerant native shrubs and grasses including buttonbush, false indigo, prairie cordgrass, and bluejoint grass. Periodic flooding and a natural fire regime control woody species.
State 2
Woody Invaded
The Woody Invaded State is dominated by a shrub and/or tree plant community. The increase and spread of shrubs and trees resulted from fire suppression and flooding reduction for 20 or more years. Woody plants can increase up to 34% from a lack of fire according to a study from 1937 to 1969, in contrast to a 1% increase on burned areas (Bragg and Hulbert, 1976). Periodic burning and significant flooding events will hinder the establishment of most woody species and favor forbs and grasses. However, not all unburned areas have a woody plant invasion. Birds, small mammals, and livestock are instrumental in the distribution and spread of seed for most tree and shrub species common to this site. The speed of encroachment varies considerably.
Characteristics and indicators. Hydrologic function in the Woody Invaded State is affected by the amount of shrub and/or tree cover compared to the Reference State. Canopy interception loss can vary from 25.4% to 36.7% (Thurow and Hester, 1997). A small rainfall event is usually retained in the foliage and does not reach the litter layer at the base of the tree. Only when canopy storage is reached and exceeded does precipitation fall to the soil surface. Interception losses associated with the accumulation of leaves, twigs, and branches at the bases of trees are considerably higher than losses associated with the canopy. The decomposed material retains approximately 40% of the water that is not retained in the canopy (Thurow and Hester, 1997). Soil properties affected include biological activity, infiltration rates, and soil fertility. The Woody Invaded State has not had tillage as a disturbance and could have plants identified in the Invasive Herbaceous State and/or the Pastureland State present on the site.
Resilience management. The Woody Invaded State is characterized as a degraded reference site that has experienced fire suppression for 20 or more years, a lack of significant flooding events, and insufficient woody plant control methods such as mechanical, chemical, biological. The lack of sunlight, due to shading by the shrubs and/or trees, will favor cool-season species that can reduce fire intensity if fire timing is during their active growth period and would help sustain the Woody Invaded State.
Community 2.1
Shrub and/or Tree
This community has numerous woody species that have encroached due to fire suppression and flooding reduction. Common species include silver maple, American elm, dogwood, sawtooth sunflower, and sedges.
State 3
Prior-Tilled
The Prior-Tilled State consists of abandoned cropland where the original plant community was destroyed through inversion by tillage but revegetation has occurred. Two plant communities are identified in the Prior-Tilled State and are identified by revegetation factors. The communities are identified as being naturally revegetated through succession (Go-back) or planted/seeded to species similar in composition to the reference plant community (Reseed). Plant species composition in the Prior-Tilled State is difficult to define due to the variability of plant communities that can exist.
Characteristics and indicators. The Prior-Tilled State is an alternative state since the energy, hydrologic, and nutrient cycles are significantly altered to that of the Reference State in its natural disturbance regime. Repeated tillage and planting of annual crops resulted in major changes in soil conditions. Reductions in organic matter, mineral levels, soil structure, oxygen levels, and water holding capacity, along with increased runoff/erosion and shifts in the populations of soil-dwelling organisms, are common in this state. The extent of these changes are dependent upon duration of cropping, crop types grown, and other management practices. Bulk density, aggregate stability, soil structure, and plant functional and structural groups are not fully restored to that of the Reference State. Mechanical tillage can destroy soil aggregation. Soil aggregates are an example of dynamic soil property change. Aggregate stability is critical for infiltration, root growth, and resistance to water and wind erosion (Brady and Weil, 2008).
Resilience management. The Prior-Tilled State is a result of a land use management decision and is sustained by diminished soil function. Implementation of practices that positively impact plant community diversity, energy flow, and nutrient and water cycle, should benefit rehabilitation. Documentation does not support rehabilitation to a Reference State within known management time frames.
Community 3.1
Go-Back
This plant community occurs on areas that were formerly farmed. When tillage operations ceased, the areas were allowed to revegetate or “go back” naturally in contrast to artificial reseeding to a selected species or group of species. The go-back process is a slow, gradual transformation that requires many years and many successional changes or stages in the plant community.
The speed and extent of revegetation depends on the size of the area, level of grazing management and the proximity of the area to existing seed sources. In the initial stages of revegetation, the site is usually dominated by annual ragweed, Canadian horseweed, common sunflower, annual marshelder and golden tickseed. Gradually these are replaced by annual grasses including prairie threeawn, prairie cupgrass, field brome and bearded sprangletop.
Usually plant succession will progress until the plant community is dominated by perennial grasses and grasslike plants including composite dropseed, foxtail barley, marsh bristlegrass, silver beardgrass, buffalograss, and Torrey’s rush. These plants can form a stable community. In time and with prescribed grazing management, other perennial grasses and forbs common in the Reference State return to the site. Go-back areas will be invaded by trees and shrubs. The more common include Siberian elm, common hackberry, eastern cottonwood, black willow, and roughleaf dogwood. Occasional burning is necessary to controlling these woody plants.
Community 3.2
Reseed
This plant community occurs on areas that were formerly farmed. When farming operations ended, the area was seeded and established to a mixture of plants, usually native species common in the Reference State. Most seeding mixtures consisted of a blend of grasses that included big bluestem, Indiangrass, switchgrass and little bluestem. In some locations seed of additional plants such as eastern gamagrass, prairie bundleflower and Maximilian sunflower were included in the mixture.
Once these areas become fully established, production is comparable to that of the Reference State.
When reseeded areas and areas supporting native rangeland exist in the same pasture, they seldom are utilized at the same intensity because domestic livestock usually prefer plants on the native rangeland areas. When feasible, reseeded plant communities should be managed as separate pastures or units. These areas are also generally productive when managed for hay production.
Some seeded areas are invaded by trees and shrubs during the establishment period of the desired plants. These invader species commonly include Siberian elm, common hackberry, eastern redcedar, eastern cottonwood, black willow, and roughleaf dogwood. Occasional burning is effective in controlling the establishment of these woody plants.
State 4
Invasive Herbaceous
The Invasive Herbaceous State is identified by a significant presence of non-native herbaceous plant species and is characterized by the composition of plant species and soil functions that govern the ecological processes.
Characteristics and indicators. Species that define this state include sericea lespedeza. Sericea lespedeza community phases are partially defined by the total production exceeding 15% by weight on a per acre basis. Ecological processes within this state that are affected and differ from the Reference State are hydrologic cycle and nutrient cycle. Water content and infiltration rates are also affected by the species in the plant community phase.
Resilience management. The Invasive Herbaceous State is sustained through continued reduction in health and vigor of native plant species and the increase in health and vigor, including seed production, of non-native herbaceous species. Ensuring a lack of forage quality due to season of grazing, and type of grazing animal, of the non-native plants will deter grazing of non-native plant species and increase grazing pressure on native plant species. A general lack of treatment measures for individual species control, maintenance, and/or eradication will also allow persistence of this state.
Community 4.1
Sericea Lespedeza
Sericea lespedeza (Lespedeza cuneata) is present at levels exceeding 15% by weight on a per acre basis and governing the ecological processes and potential uses of this community. Sericea lespedeza is invasive and listed as a statewide noxious weed in Kansas. It competes with the native plant community for sunlight, water, and nutrients, and produces allelopathic compounds (toxic chemicals that negatively impact the germination and/or growth of other plants). It also contains tannins, that limit palatability, and produces copious amounts of seed that remain viable in the soil for decades. This species will quickly invade rangelands without proactive control measures.
Resilience management. Sericea lespedeza (Lespedeza cuneata) is extremely competitive with its allelopathic nature, lower palatability compared to native species, and good seedling vigor. To prevent further loss of native plant composition, ensure native plant vigor remains high via a forage-animal balance based on forage composition and palatability, utilize spot application of herbicides to control new and existing sericea lespedeza plants, and consider diversifying grazing livestock type. Control measures for sericea lespedeza involve herbicide application following extension recommendations and product label for proper rates and timing. Utilization and control can also be provided through sheep and goat grazing. Conventional management practices such as prescribed grazing with cattle and dormant-season fire have been less than effective in preventing the spread of sericea lespedeza in rangelands. Some suppression of sericea lespedeza has been observed after mowing or summer burning. Late summer fire significantly reduces seed production the year of burn. An integrated approach is needed when treating this species.
State 5
Cropland
The Cropland State is dominated by row crops such as corn, wheat, and soybeans. It occurs on areas that have been mechanically tilled and converted to agricultural cropland. After tillage, efforts are then taken to plant various crops through a conservation cropping system.
This state is common. Many sites have been converted to agricultural cropland.
Resilience management. This state is a result of a land use management decision.
Community 5.1
Cropland
This community occurs on areas where land use has been converted through mechanical tillage to intensive agriculture by conservation cropping. Primary crops are corn, wheat, and soybeans.
State 6
Pastureland
The Pastureland State is identified by a significant presence of non-native herbaceous plant species and is characterized by the composition of plant species, agronomic inputs from direct fertilization, and soil functions that govern the ecological processes. Sites consisting of introduced species and managed for their continued presence or spread should not be evaluated within this model and instead, consider using a separate land use model such as Pasture.
Characteristics and indicators. Tall fescue, smooth brome, and Kentucky bluegrass are partially defined by the total production exceeding 40% by weight on a per acre basis. Ecological processes within this state that are affected and differ from the Reference State are hydrologic cycle and nutrient cycle. Water content and infiltration rates are also affected by the species in the plant community phase.
Resilience management. Pastureland is sustained through continued reduction in health and vigor of native plant species and the increase in health and vigor, including seed production, of non-native herbaceous species. Agronomic inputs from direct fertilization or nutrient-rich runoff from adjacent crop fields will provide advantages for non-native cool-season grass species growth. Ensuring a lack of forage quality due to season of grazing, type of grazing animal, or chemical composition of the non-native plants will deter grazing of non-native plant species and increase grazing pressure on native plant species. A general lack of treatment measures for individual species control, maintenance, and/or eradication will also allow persistence of this state.
Community 6.1
Fescue, Brome, Bluegrass
Tall fescue, smooth brome, and Kentucky bluegrass (all being cool-season grasses) are present at levels exceeding 40% by weight on a per acre basis and are governing the ecological processes and potential uses of this community. Timing of plant growth has shifted from summer (May through August) and now mostly occurs in spring and fall (March to May and September to November). Fire intensity of late spring burns can be greatly impeded due to the significant quantity of cool-season grass present. Any one or a combination of these species can be considered an invaded community. Soil dynamic property changes include biological activity and soil fertility.
Resilience management. Tall fescue, smooth brome, and Kentucky bluegrass are sustained or increased with nutrient additions and absence of fire. To prevent further loss of native plant composition, avoid nutrient additions, ensure native plant vigor remains high via a forage-animal balance based on forage composition and seasonal availability, utilize herbicides when natives are dormant but cool-seasons are actively growing, and utilize consecutive late spring prescribed burns. Chemical control will involve herbicide application following extension recommendations and product label for proper rates and timing. Intensifying grazing pressure (leaf removal of cool-season grasses) during the spring and fall and removing grazing pressure during the summer will reduce cool-season grass vigor and allow native warm-season plants an opportunity to maximize growth and gain vigor. Prescribed burning will require sufficient standing dead material in order to conduct a burn in late spring as warm-season grasses initiate growth. If the goal is continued presence or spread of tall fescue, smooth brome, or Kentucky bluegrass, consider using a separate land use model such as Pasture.
Transition T1A
State 1 to 2
Long term fire suppression (20+ years) and no significant flooding events will transition the Reference State to a Woody Invaded State. A lack of fire and flooding events will allow woody species to establish and increase, shifting the site to dominant trees and shrubs with a reduction in desirable grasses and forbs in the understory.
Transition T1B
State 1 to 4
A transition from Reference to an Invasive Herbaceous State occurs when the site is invaded by Sericea lespedeza with the total production exceeding 15% by weight on a per acre basis.
Transition T1C
State 1 to 5
Tillage (or no-till if that management style is preferred) and seeding of agricultural crops will transition this site from a Reference State to a Cropland State.
Restoration pathway R2A
State 2 to 1
Restoration actions to return to a Reference State may include machinery woody removal and prescribed fire every 1-3 years. A significant flooding event may also remove a large number of woody species. Efforts will be costly, labor-intensive, and can take many years, if not decades. Once canopy levels reach greater than 20 percent, estimated cost to remove trees is very expensive and includes high energy inputs.
Transition T2A
State 2 to 5
Tillage (or no-till if that management style is preferred) and seeding of agricultural crops will transition this site from a Woody Invaded State to a Cropland State.
Transition T4A
State 4 to 5
Tillage (or no-till if that management style is preferred) and seeding of agricultural crops will transition this site from an Invasive Herbaceous State to a Cropland State.
Transition T5A
State 5 to 3
Allowing the site to naturally revegetate as it regenerates, or reseeding the site with native grasses and forbs with proper management afterwards will transition this site from a Cropland to a Prior-Tilled State.
Transition T5B
State 5 to 6
Seeding of cool season grasses and forbs and proper pasture management will transition this Cropland to a Pastureland.
Transition T6A
State 6 to 4
A transition from Pastureland to an Invasive Herbaceous State occurs when the site is invaded by Sericea lespedeza with the total production exceeding 15% by weight on a per acre basis.
Transition T6B
State 6 to 5
Tillage (or no-till if that management style is preferred) and seeding of agricultural crops will transition this site from a Pastureland to a Cropland.