Ecological dynamics
The Sandy Lowland ecological sites developed under Central Great Plains climatic conditions, light to severe grazing by bison and other large herbivores, sporadic natural or man caused wildfires, and other biotic and abiotic factors which typically influence soil/site development. This continues to be a disturbance driven site, by herbivory, fire, and variable climate. Changes occur in the plant communities due to weather variations, impacts of native and/or exotic plant and animal species, and management actions.
One of the primary impacts to this site introduced by European settlers is season long continuous grazing by domestic livestock. This management practice causes the repeated removal of the growing point and excessive defoliation of the leaf area of individual tall warm-season grasses. The resulting reduction of the ability of the plants to harvest sunlight depletes the root reserves, subsequently decreasing the root mass. This negatively impacts the ability of the plants to compete for life sustaining nutrients, resulting in declining vigor and eventual mortality. The space created in the vegetative community is then occupied by a species that evades the negative grazing impacts by a growing season adaptation such as a cool season, shorter structure, or reduced palatability mechanism.
The State and Transition Model (STM) is depicted following this section and includes a Reference State (1), a Native/Invaded Grass State (2), a Sod-busted State (3), and an Invaded Woody State (4). Each state represents the crossing of a major ecological threshold due to alteration of the functional dynamic properties of the ecosystem. The main properties observed to determine this change are the soil and vegetative communities and the hydrologic cycle. The STM illustrates the common plant communities that can occur on the site and the transition pathways between communities (Bestelmeyer, 2010). The ecological processes will be discussed in more detail in the plant community descriptions following the diagram.
Each state may have one or more vegetative communities which fluctuate in species composition and abundance within the normal parameters of the state. Within each state, communities may degrade or recover in response to natural and man caused disturbances such as variation in the degree and timing of herbivory, presence or absence of fire, and climatic and local fluctuations in the precipitation regime.
Interpretations are primarily based on the Reference State and have been determined by study of rangeland relic areas, areas protected from excessive disturbance, and areas under long term rotational grazing regimes. Trends in plant community dynamics have been interpreted from heavily grazed to lightly grazed areas, seasonal use pastures, and historical accounts. Plant communities, states, transitional pathways, and thresholds have been determined through similar studies and experience.
State 1
Reference State
The Reference State (1) describes the range of vegetative community phases that occur on the Sandy Lowland site where the natural processes are mostly intact. The Reference Community (1.1) is a representation of the native plant community phase that occupies a site that has been minimally altered by management. The Degraded Native Grass (1.2), the At-Risk (1.3), and the Excessive Litter (1.4) Communities are the phases that result from management decisions that are unfavorable for a healthy Reference Community (1.1). High perennial grass cover and production allows for increased soil moisture retention, vegetative production, and overall soil quality.
Community 1.1
Reference Community
Figure 8. Sandy Lowland ecological site, Reference Community (1.1), eastern Kansas, MLRA 106. Photo courtesy of Dave Kohake.
The Reference or Tallgrass Native Prairie Community (1.1) serves as a description of the native plant community that naturally occurs on the site when the natural disturbance regimes are intact, or closely mimicked by management practices. This phase is dynamic, with fluid relative abundance and spatial boundaries between the dominant structural vegetative groups. These fluctuations are primarily driven by different responses of the species to changes in precipitation timing and abundance, and fire and grazing events.
The potential vegetation consists of approximately 70 to 85 percent grasses and grass-likes, 5 to15 percent forbs, 0 to 5 percent shrubs, and 0 to 2 percent deciduous trees. Big bluestem, Indiangrass, and switchgrass are the primary herbaceous species in this community. Secondary species include little bluestem, sideoats grama, and blue grama. Elm, willow, and cottonwood are often part of this community as well. The site has a fairly diverse forb population.
This plant community is highly productive, diverse, and resistant to short term stresses such as drought and short periods of heavy stocking. The well-developed root systems support resiliency when allowed adequate recovery periods between grazing events. When exposed to long term or frequent over grazing events without adequate rest, this plant community will degrade.
The annual vegetative production of this community averages 6,000 lbs/acre.
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Community 1.2
Degraded Native Grass Community
Figure 10. Sandy Lowland ecological site, Degraded Native Grass Community (1.2), eastern Kansas, MLRA 106. Photo Courtesy of Dave Kohake
In the Degraded Native Grass Community (1.2), warm-season tall grasses, such as big bluestem, switchgrass, and Indiangrass, lose productive capacity through loss of vigor and reproductive potential. The proximity of the water table for the deep-rooted tall grasses on this site helps to sustain species as subdominant. However, mid grasses such as little bluestem and sideoats grama increase to become the dominant functional group. Thin paspalum, sand lovegrass, blue grama, and sand dropseed begin to increase in abundance. Forb diversity is reduced.
This community phase signals a significant loss of production as warm-season tall grasses decrease while warm-season mid and short grasses and cool-season grasses increase. The composition of the forb component remains diverse, and the woody component may increase. While this plant community is less productive and less diverse than the representative plant community, it remains sustainable in regard to site and soil stability, watershed function, and biologic integrity.
Community 1.3
At-Risk Community
Figure 11. Sandy Lowland ecological site, At-Risk Community (1.3), eastern Kansas, MLRA 106. Photo courtesy of Dave Kohake.
In the At-Risk Community (1.3), the more palatable warm-season tall grasses have been reduced to a minor component by continued defoliation during their critical growth periods. Warm-season short grasses and cool-season grasses increase significantly. Blue grama grasses, hairy grama, sand dropseed, sand paspalum, and sand lovegrass become the dominant species. Cheatgrass and other non-native cool-season grasses may begin to invade the site. The deciduous tree component may increase significantly and if a seed source is present, eastern red cedar may begin to encroach.
Soil health is affected by reduced efficiency in the nutrient, mineral, and hydrologic cycles as a result of decreases in plant litter and rooting depths. Total annual vegetative production declines significantly. Without a management change, this community is at risk to degrade to the Native/Invaded Grass State (2).
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Community 1.4
Excessive Litter Community
The Excessive Litter Community (1.4) develops when the natural disturbances of herbivory and fire are removed from the system for extended periods of time (five years or more). Litter significantly exceeds the amount expected on the site and the species present can tolerate a thatch layer. Individual plants tend to be clumped and there is an excessive amount of litter. Species that cannot tolerate an extensive litter layer have low vigor and reduced productivity.
Once the undisturbed litter layer develops to a certain level, a significant amount of precipitation is held in this layer increasing evaporation, limiting soil available moisture, and simulating drought conditions. If herbivory or fire are not reintroduced, the plant community will experience a significant amount of death loss.
Pathway 1.1A
Community 1.1 to 1.2
Degraded Native Grass Community
A shift from the Reference Community (1.1) to the Degraded Native Grass Community (1.2) occurs with continuous, season long grazing or rotational grazing with inadequate growing season recovery periods (deferment). Haying with inadequate recovery periods between cuttings will also cause this change.
Pathway 1.1B
Community 1.1 to 1.4
Prolonged (greater than five years) interruption of the natural disturbances of herbivory and fire will convert the Reference Community (1.1) to the Excessive Litter Community (1.4).
Pathway 1.2A
Community 1.2 to 1.1
Degraded Native Grass Community
A shift from the Degraded Native Grass Community (1.2) toward the Reference Community (1.1) can be achieved through prescribed grazing. Applying grazing pressure during the rapid growth period of the less productive cool-season grasses while allowing rest during the warm-season portion of the growing season favors the more productive warm-season tall grasses. This grazing strategy will enable the deeply rooted, warm-season tall grasses to out compete the shallower rooted warm-season mid and short grasses and the cool season grasses. Appropriately timed prescribed fire will accelerate this process.
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Pathway 1.2B
Community 1.2 to 1.3
Degraded Native Grass Community
Long-term, continuous season long grazing, rotational grazing with inadequate growing season recovery periods (deferment) further degrades the site and moves the Degraded Native Grass Community (1.2) to the At-Risk Community (1.3). Haying with inadequate recovery periods between cuttings will also cause this change.
Pathway 1.2C
Community 1.2 to 1.4
Prolonged (greater than five years) interruption of the natural disturbances of herbivory and fire will convert the Degraded Native Grass Community (1.2) to the Excessive Litter Community (1.4).
Pathway 1.3A
Community 1.3 to 1.2
Degraded Native Grass Community
Reversing the downward trend that moved the Degraded Native Grass Community (1.2) to the At-Risk Community (1.3) can be achieved with prescribed grazing early and late in the growing season to reduce undesirable cool-season grasses. Targeting the peak growth period of cool-season grasses with high intensity grazing events followed by rest will allow the tall native warm-season grasses to rejuvenate. Appropriately timed prescribed fire will accelerate this process.
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Pathway 1.3B
Community 1.3 to 1.4
Prolonged (greater than five years) interruption of the natural disturbances of herbivory and fire will convert the At-Risk Community (1.3) to the Excessive Litter Community (1.4).
Pathway 1.4A
Community 1.4 to 1.1
Reintroduction of the natural processes of herbivory and fire will allow the vegetation to return of the Excessive Litter Community (1.4) to the Reference Community (1.1).
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Pathway 1.4B
Community 1.4 to 1.2
Reintroduction of the natural processes of herbivory and fire will allow the vegetation of the Excessive Litter Community (1.4) to return to the Degraded Native Grass Community (1.2).
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Pathway 1.4C
Community 1.4 to 1.3
Reintroduction of the natural processes of herbivory and fire will allow the vegetation of the Excessive Litter Community (1.4) to return to the At-Risk Community (1.3).
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State 2
Native/Invaded Grass State
The Native/Invaded Grass State (2) has been degraded from the Reference State (1) and most of the native, warm-season, tall and mid grasses have been replaced by less productive warm-season short grasses and cool-season grasses. The loss of warm-season, tall and mid grasses has negatively impacted energy flow and nutrient cycling. Patches of open sand may be present.
Community 2.1
Shortgrass Sod/Invaded Grass Community
Figure 13. Sandy Lowland ecological site, Shortgrass Sod/Invaded Grass Community (2.1) with areas of open sand, MLRA 106.Photo courtesy of Dave Kohake,
Figure 14. Sandy Lowland, Shortgrass Sod/Invaded Grass Community (2.1) with patches of invasive woody species, MLRA 106 Photo courtesy of Dave Kohake.
The Shortgrass Sod/Invaded Grass Community (2.1) represents a shift from the Reference State (1) across a plant community threshold. With continued grazing pressure, blue grama, sand dropseed, and annual grasses will become the dominant grasses. Kentucky bluegrass may be co-dominant and cheatgrass, windmill grass, sandbur, or other annuals may become dominant in patches. Only trace remnants of the more palatable warm-season mid grasses such as sideoats grama and little bluestem will be present, if at all. Open sand may be present.
State 3
Sod-busted State
The threshold to the Sod-busted State (3) is crossed as a result of mechanical disturbance to facilitate production agriculture. Extensive areas of this ecological site were plowed and converted to crop production by early European settlers and their subsequent generations. In addition to permanently altering the existing vegetative community, repeated tillage negatively impacted soil properties. Reductions in organic matter, mineral levels, soil structure, oxygen levels, and water-holding capacity along with increased runoff and erosion as well as shifts in the populations of soil dwelling organisms were common on these sites. The extent of these changes depended upon the duration of cropping as well as crops grown and other management practices.
If farming operations are suspended, the site can be abandoned or seeded to permanent vegetation. Seedings are either a tame pasture forage mixture, the Seeded Pasture Community (3.2), or a mixture of native grasses and forbs, the Reseeded Native Grass Community (3.1). Abandonment results in the Natural Reclamation Community (3.3). Permanent alterations of the soil, plant community, and the hydrologic cycle make restoration to the Reference State (1) extremely difficult, if not impossible.
Community 3.1
Reseeded Native Grass Community
The Reseeded Native Grass Community (3.1) does not contain native remnants, and varies considerably depending upon the seed mixture, the degree of soil erosion, the age of the stand, fertility management, and past grazing management. Prescribed grazing with adequate recovery periods will be required to maintain productivity and desirable species.
Native range and grasslands seeded to native species are ecologically different and should be managed separately. Factors such as functional group, species, stand density, and improved varieties all impact the production level and palatability of the seedings. Species diversity is often limited, and when grazed in conjunction with native rangelands, uneven forage utilization may occur.
Total annual production during an average year varies significantly depending upon precipitation, management, and grass species seeded.
Community 3.2
Seeded Pasture Community
The Seeded Pasture Community (3.2) does not contain native remnants and varies considerably depending upon the extent of soil erosion, the species seeded, the quality of the stand that was established, the age of the stand, and management of the stand since establishment.
There are several factors that make seeded tame pasture a different grazing resource than native rangeland and land seeded to a native grass mixture. Factors such as species selected, stand density, improved varieties, and harvest efficiency all impact production levels and palatability. Species diversity on seeded tame pasture is often limited to a few species. When seeded pasture and native rangelands or seeded pasture and seeded rangeland are in the same grazing unit, uneven forage utilization will occur. Improve forage utilization and stand longevity by managing this community separately from native rangelands or land seeded to native grass species.
Total annual production during an average year varies significantly depending on the level of management and species seeded. Improved varieties of warm-season or cool-season grasses are recommended for optimum forage production.
Community 3.3
Natural Reclamation Community
The Natural Reclamation Community (3.3) consists of annual and perennial weeds and less desirable grasses. These sites have been farmed and abandoned without being reseeded. Soil organic matter and carbon reserves are reduced, soil structure is changed, and a plowpan or compacted layer can form, which decreases water infiltration. Residual synthetic chemicals may remain from farming operations. In early successional stages, this community is not stable. The hazard of erosion is a concern.
Total annual production during an average year varies significantly depending on the succession stage of the plant community and any management applied to the system.
State 4
Invaded Woody State
The Invaded Woody State (4) is the result of woody encroachment. Once the tree canopy cover reaches 15 percent with an average tree height exceeding five feet, the threshold is crossed. Woody species are encroaching due to lack of prescribed fire and other brush management practices. Typical ecological impacts are a loss of native grasses, degraded forage productivity, and reduced soil quality.
Prescribed burning, wildfire, timber harvest, and brush management will move this state toward a grass dominated state. If the Invaded Woody State (4) transitioned from the Native/Invaded Grass State (2) or the Sod-busted State (3), the land cannot be restored to the Reference State (1) as the native plant community, soils, and hydrologic function have been too severely impacted prior to the woody encroachment to allow restoration to the Reference State (1). The Invaded Woody State (4) includes the Deciduous Woody Community (4.1) and the Eastern Red Cedar Community (4.2).
Community 4.1
Deciduous Woody Community
Figure 15. Sandy Lowland ecological site, Deciduous Woody Community (4.1), MLRA 106, eastern Kansas. Photo courtesy of Dave Kohake.
The Deciduous Woody Community (4.1) has at least a 15 percent woody canopy cover. Willow, elm, and cottonwood are the primary species in this community but invasive deciduous trees including Siberian elm, honeylocust, and roughleaf dogwood may be present.
Re-sprouting brush must be chemically treated immediately after mechanical removal to achieve effective treatment. The forb component will initially increase following tree removal. To prevent return to a woody dominated community, ongoing brush management such as hand cutting, chemical spot treatments, or periodic prescribed burning is required. In higher canopy cover situations, the soil erosion will increase in relation to most of the plant communities from which this plant community originated. The water cycle is also significantly altered under higher canopy cover. Infiltration is reduced and runoff is typically increased because of a lack of herbaceous cover and the rooting structure provided by the herbaceous species. Total annual production during an average year varies significantly, depending on the production level prior to encroachment and the percentage of canopy cover.
In the absence of fire and brush management, this site is very conducive to eastern red cedar seedling invasion, especially when adjacent to a seed source. Eastern red cedar can eventually dominate the site, resulting the Eastern Red Cedar Community (4.2), which drastically reduces forage production and has limited value for either livestock grazing or wildlife habitat.
Community 4.2
Eastern Red Cedar Community
Willow, elm, and cottonwood may be present, but have generally been replaced by eastern red cedars. Eastern red cedar will eventually dominate the entire site, resulting in a closed canopy monoculture which drastically reduces forage production and has limited value for either livestock grazing or wildlife habitat. Due to fire suppression over many years, this plant community will develop extensive ladder fuels which can lead to a removal of most tree species with a wildfire. With properly managed intensive grazing, encroachment of deciduous trees will be minimal; however, this will not impact encroachment of conifer species. The herbaceous component decreases proportionately in relation to the percent canopy cover, with the reduction being greater under a conifer overstory. Eastern red cedar control can usually be accomplished with prescribed burning while the trees are six feet tall or less and fine fuel production is greater than 1,500 pounds per acres. Larger red cedars can also be controlled with prescribed burning, but successful application requires the use of specifically designed ignition and holding techniques (https://www.loesscanyonsburngroup.com).
Re-sprouting brush must be chemically treated immediately after mechanical removal to achieve effective treatment. The forb component will initially increase following tree removal. To prevent return to a woody dominated community, ongoing brush management such as hand cutting, chemical spot treatments, or periodic prescribed burning is required. This plant community is resistant to change and resilient given normal disturbances. In higher canopy cover situations, the soil erosion will increase in relation to most of the plant communities from which this plant community originated. The water cycle is also significantly altered under higher canopy cover. Infiltration is reduced and runoff is typically increased because of a lack of herbaceous cover and the rooting structure provided by the herbaceous species. Total annual production during an average year varies significantly depending on the production level prior to encroachment and the percentage of canopy cover.
Pathway 4.1A
Community 4.1 to 4.2
Continued absence of fire and brush management will allow eastern red cedar to increase in abundance and become dominant in the understory. The eastern red cedar will out compete the deciduous seedlings and eastern red cedar will eventually become a near monoculture, moving the Deciduous Woody Community (4.1) to the Eastern Red Cedar Community (4.2).
Pathway 4.2A
Community 4.2 to 4.1
Brush management or prescribed fire designed to control the eastern red cedar while leaving the deciduous trees intact will move the Eastern Red Cedar Community (4.2) to the Deciduous Woody Community (4.1).
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Transition T1A
State 1 to 2
Heavy, continuous grazing or haying without adequate recovery periods will cause the Reference State (1) to lose a significant proportion of warm-season, tall and mid grass species and cross a threshold to the Native/Invaded State (2). Water infiltration and other hydrologic functions will be reduced due to the root matting presence of sod-forming grasses. With the decline and loss of deeper penetrating root systems, soil structure and biological integrity are degraded to the point that recovery is unlikely. Once this occurs, it is highly unlikely that grazing management alone will return the community to the Reference State (1).
Transition T1B
State 1 to 3
The Reference State (1) is significantly altered by mechanical tillage converting site to the Sod-busted State (3) to facilitate production agriculture. The disruption to the plant community, the soil, and the hydrology of the system make restoration to a true reference state unlikely.
Transition T1C
State 1 to 4
Disruption of the natural fire regime and the encroachment of invasive exotic and native woody species can cause the Reference State (1) to shift to the Invaded Woody State (4).
Transition T2A
State 2 to 3
The Native/Invaded State (2) is significantly altered by mechanical tillage converting site to the Sod-busted State (3) to facilitate production agriculture. The disruption to the plant community, the soil, and the hydrology of the system make restoration to a true reference state unlikely.
Transition T2B
State 2 to 4
Disruption of the natural fire regime and the encroachment of invasive exotic and native woody species can cause the Native/Invaded State (2) to transition to the Invaded Woody State (4).
Transition T3A
State 3 to 4
Disruption of the natural fire regime and the encroachment of invasive exotic and native woody species can cause the Sodbusted State (3) to shift to the Invaded Woody State (4).
Restoration pathway R4A
State 4 to 1
Prescribed burning, wildfire, timber harvest and brush management will move the Invaded Woody State (4) toward the Reference State (1). Land that transitioned to the Invaded Woody State (4) from the Native/Invaded State (2) or the Sod-busted State (3) cannot be restored to the Reference State (1) as the native plant community, soils, and hydrologic function have been too severely impacted prior to the woody encroachment to allow restoration to the Reference State.
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Restoration pathway R4B
State 4 to 2
Prescribed burning, wildfire, timber harvest and brush management will move the Invaded Woody State (4) toward the Native/Invaded State (2). Land that transitioned to the Invaded Woody State (4) from the Native/Invaded State (2) or the Sod-busted State (3) cannot be restored to the Reference State (1) as the native plant community, soils, and hydrologic function have been too severely impacted prior to the woody encroachment to allow restoration to the Reference State.
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Restoration pathway R4C
State 4 to 3
Prescribed burning, wildfire, timber harvest and brush management will move the Invaded Woody State (4) toward the Sod-busted State (3). Land that transitioned to the Invaded Woody State (4) from the Native/Invaded State (2) or the Sod-busted State (3) cannot be restored to the Reference State (1) as the native plant community, soils, and hydrologic function have been too severely impacted prior to the woody encroachment to allow restoration to the Reference State.
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