Ecological dynamics
The Novaculite Upland reference state consists of a pine forest, characterized by a shortleaf pine overstory with a herbaceous forest floor. Loblolly pine and hardwood tree species can also be found on upland sites (Edlredge, 1937). Native grass species such as big bluestem, switchgrass, little bluestem, and Indiangrass are found in the herbaceous layer. (Arkansas Geological Survey, 2005).
Fire has a significant influence on this ecological site. The historical average fire-return interval was likely between 3 and 25 years (Guyette and Spetich, 2003; Hallgren, DeSantic, and Burton, 2012). These wildfires would occur naturally through lightning strikes, but the majority were probably ignited by anthropogenic sources (DeSantis, Hallgren, and Stahle, 2010). Native species evolved with and responded well to fires (Spetich and Hong He, 2008; Engle and Bidwell, 2001). Fires on upland ecological sites are likely moderate to low severity, due to forested conditions and lower amounts of ground vegetation (Carey, 1992).
Climate related events, such as hail-storms, tornados, thunderstorms, and extreme precipitation, occur on these sites. Hail-storms can reduce canopy size, increase litter deposition, and increase tree bark removal. When paired with other disturbances, such as fire, the effects on tree species were much greater than in areas not affected by the hail-storm (Gower et al., 2015). Tornados have been shown to change plant community compositions in savanna ecosystems, favoring hardwoods and eliminating softwoods (Liu et al., 1997). Thunderstorms greatly effect ecosystem dynamics. Thunderstorms generally occur during summer months but can occur during every season. If a fire is started by a lightning strike, there will be different effects in the ecosystem depending on the season (Hiers, Wyatt, and Mitchell, 2000).
Grazing and farming can occur on this ecological site. Changes to the ecological dynamics are proportional to the intensity of livestock grazing and can be accelerated by overgrazing (Angerer, Fox, and Wolfe, 2013; Kohl, 2016). For example, desirable grasses and forbs are repeatedly grazed by livestock, weakening, and potentially killing or replacing these species with less desirable species (Smith, 1940).
A state and transition model has been created to explain this ecological site. However, sparse data availability only allowed basic principles to be explored and a small number of species to be recorded. More data will be collected to provide a greater understanding of the ecological dynamics, as well as the resources consumption and distribution.
State 1
Reference
The Reference State is representative of the natural range of variability without major anthropogenic influences.
Drivers: Fire frequency between 3 and 25 years, climate (decadal scale), insect and disease presence or establishment, and wildlife grazing or browsing.
Feedbacks: Fire-tolerant species dominate the ecological site. Wildlife grazing or browsing decreases the amount of grass available, decreasing fire intensity and causing wildlife migration to a new grazing location.
Characteristics and indicators. The reference state consists of a hardwood forest, characterized by mixed hardwood species. Gaps in the canopy allow sunlight to reach the herbaceous layer, allowing grass and forb species to grow. Softwood species such as loblolly pine and shortleaf pine are also present.
Community 1.1
Post Oak/Little Bluestem
This community phase is dominated by oak trees and warm-season, perennial tallgrasses. Dominant grasses are little bluestem, big bluestem, Indiangrass, and switchgrass. Common trees species include post oak, blackjack oak, white oak, and red oak.
Community 1.2
Post Oak-Eastern Redcedar (at-risk community)
This community phase has a moderately closed canopy with an understory of tallgrasses and midgrasses. The absence of fire has allowed post oak, blackjack oak, and eastern redcedar densities to increase. The competition from the increased canopy has led to a decrease in herbaceous plants.
Pathway 1.1A
Community 1.1 to 1.2
This pathway consists of an absence of fire and the natural regeneration of woody species. It may also be coupled with excessive grazing pressure.
Pathway 1.2A
Community 1.2 to 1.1
This pathway consists of periodic fire that reduces the amount of woody vegetation. Drought and insect or disease outbreaks may also result in a reduced woody canopy.
| Prescribed Burning |
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| Prescribed Grazing |
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State 2
Encroached
The encroached state is dominated by woody species.
Driver: Absence of wildfire, seed dispersal by wildlife, climate (decadal scale), and canopy density.
Feedbacks: Woody species dominate the ecological site, shading herbaceous species. As herbaceous species are outcompeted for resources, fire frequency decreases. Nutrient and water cycles are controlled by woody species.
Characteristics and indicators. The Encroached State consists of many woody species, especially eastern redcedar, where there is significant canopy closure. Time and fire frequency determine the community phases, species abundance, and species variation. As the woody canopy increases the hydrology of the site is altered. The increased canopy intercepts most of the precipitation. Understory species have less available water for growth and must compete with an extensive overstory root system.
Community 2.1
Post Oak- Eastern Redcedar
This community phase consists of oak, hickory, beech, and eastern redcedar. The canopy increases, causing a decrease in the herbaceous ground cover species. Eastern redcedar increases in size and quantity.
Community 2.2
Eastern Redcedar- Post Oak
This community phase is dominated by eastern redcedar. Oak, hickory, and beech species may be present. Oak, hickory, and beech species experience reduced vigor and reproductive capacity due to shading and competition from eastern redcedar.
Pathway 2.1A
Community 2.1 to 2.2
This pathway consists of an absence of fire. The absence of fire and natural regeneration allows woody vegetation cover to increase.
Pathway 2.2A
Community 2.2 to 2.1
This pathway experiences a decrease in canopy cover, increasing the amount of sunlight that reaches the herbaceous vegetation on the ground. An increase in the herbaceous vegetation can lead to fires that reduce woody vegetation. Possible causes of decreased canopy cover are fire and mechanical tree removal.
State 3
Pasture
The Pasture State is characterized by the dominance of improved forage species. The quality and quantity of forb, grass, and legume species within this state will depend on the level of management inputs including seeding, weed management, and land uses. Species of both warm-season and cool-season grasses are feasible for these sites.
Drivers: Mechanical soil disturbance and seed planting, climate (decadal scale), seed dispersal, and wildlife or livestock grazing or browsing.
Feedbacks: Land managers use mechanical and chemical equipment to increase forage. Inputs of fertilizer and brush management are required to maintain high productivity. Wildlife and livestock grazing and browsing decrease the amount of available forage.
Characteristics and indicators. The Pasture State consists of species that are grown for specific management goals, mainly livestock grazing. Common pasture species include buffalograss, western wheatgrass, little bluestem, sideoats grama, Bermudagrass, and bahiagrass. Quality and quantity of forb, grass, and legume species within this state depend on the level of management inputs (seeding, weed management, and land uses). Species of both warm-season and cool-season grasses are feasible for these sites.
Community 3.1
Bermudagrass
Herbaceous species have been planted to maximize forage production for grazing livestock.
Community 3.2
Bermudagrass/ Post Oak- Eastern Redcedar
Herbaceous species have been planted to maximize forage production for grazing livestock. Management decisions allow the growth of woody species, such as eastern redcedar and oaks.
Community 3.3
Eastern Redcedar- American Elm- Post Oak/ Bermudagrass
Herbaceous species have been planted to maximize forage production for grazing livestock. Improper pasture management and time have allowed for the growth of woody species such as eastern redcedar, oaks, and American elm. Woody species encroach on the pasture and dominate resources that were previously utilized by forage species.
Pathway 3.1A
Community 3.1 to 3.2
This pathway consists of an absence of fire, improper management, and natural regeneration.
Pathway 3.2A
Community 3.2 to 3.1
This pathway consists of the removal or reduction of woody species.
Pathway 3.2B
Community 3.2 to 3.3
This pathway consists of an absence of fire, improper management, and natural regeneration.
Pathway 3.3A
Community 3.3 to 3.1
This pathway consists of the removal or reduction of woody species.
Pathway 3.3B
Community 3.3 to 3.2
This pathway consists of the removal or reduction of woody species.
State 4
Plantation
The plantation state is characterized by the planting of merchantable trees species. The most common species for a plantation is loblolly pine. Community phases differ by tree type (softwood or hardwood) and the harvesting process.
Drivers: Prescribed fires, pest management, vegetation management, canopy density.
Feedbacks: Timber harvesting. Planted tree species dominate this ecological site, shading out other vegetation. Anthropogenic management decreases competition with other species and assists in growth.
Characteristics and indicators. A plantation state consists of tree species that are planted and managed to maximize the production of merchantable timber. The most common plantation species is loblolly pine, followed by hardwood trees. Community phases differ by tree type (softwood or hardwood), timber harvest method, management, and reforesting practices.
Community 4.1
Loblolly Pine
Loblolly pine is planted to maximize timber production.
Dominant plant species
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loblolly pine (Pinus taeda), tree
Transition T1A
State 1 to 2
Trigger: The absence of fire allows woody species to increase and outcompete herbaceous species for nutrients, water, and sunlight.
Slow variables: Increased competition for sunlight, nutrients, and moisture resources. Increased overstory competition results in decreased vigor and reproductive capacity of herbaceous understory species.
Thresholds: Nutrient cycles shift from grass-and-leaf dominance to leaf-and-needle dominance. Increased woody canopy cover alters hydrologic cycles, potentially increasing runoff, decreasing infiltration, and increasing precipitation interception to woody species.
Transition T1B
State 1 to 3
Trigger: Mechanical and chemical woody vegetation suppression, tillage, and annual forage species introduction.
Slow Variables: Increase production and management of forage species.
Thresholds: Changes in soil properties, such as structure, organic matter, and nutrient cycling, as well as changes in type and frequency of disturbance.
| Brush Management |
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| Prescribed Burning |
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| Land Clearing |
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| Prescribed Grazing |
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Transition T1C
State 1 to 4
Trigger: Native tree removal, mechanical and chemical woody vegetation suppression, introduce plantation tree species.
Slow Variables: Increased production and management of plantation species.
Thresholds: Changes in soil properties such as structure, organic matter, and nutrient cycling as well as changes in type and frequency of disturbance.
Restoration pathway R2A
State 2 to 1
Restoration efforts should begin through the mechanical and chemical treatment of undesirable woody vegetation and by seeding native species. Following the initial treatment of the ecological site, restoration must be accompanied by grazing management and the reintroduction of historic disturbance regimes. Returning to a historic fire interval through prescribed burning assists in woody vegetation suppression and invasive species management.
| Brush Management |
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| Prescribed Burning |
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Transition T2A
State 2 to 3
Trigger: Mechanical and chemical woody vegetation treatment, tillage, and forage species introduction.
Slow Variables: Increase production and management of forage species.
Thresholds: Changes in soil properties, such as structure, organic matter, and nutrient cycling, as well as changes in type and frequency of disturbance.
| Brush Management |
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| Prescribed Burning |
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| Land Clearing |
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| Prescribed Grazing |
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Transition T2B
State 2 to 4
Trigger: Native tree removal, mechanical and chemical woody vegetation suppression, introduce plantation tree species.
Slow Variables: Increased production and management of plantation species.
Thresholds: Changes in soil properties such as structure, organic matter, and nutrient cycling as well as changes in type and frequency of disturbance.
Transition T3B
State 3 to 2
Triggers: Lack of management or abandonment.
Slow Variables: Increase in the establishment and size of woody species.
Thresholds: Woody species dominate ecological processes. This reduces vigor and reproduction of understory species due to shading and increased competition for soil moisture, nutrients, and sunlight.
Transition T3A
State 3 to 4
Trigger: Forage species removal and suppression, mechanical and chemical woody vegetation suppression, introduce and manage plantation tree species.
Slow Variables: Increased production and management of plantation species.
Thresholds: Changes in soil properties such as structure, organic matter, and nutrient cycling as well as changes in kind and frequency of disturbance.
Transition T4A
State 4 to 2
Triggers: Lack of management or abandonment.
Slow Variables: Increase in the establishment and size of woody species.
Thresholds: Woody species dominant ecological processes resulting in reduced vigor and reproduction of herbaceous species in the understory due to shading and increased competition for soil moisture, nutrients, and sunlight.
Transition T4B
State 4 to 3
Trigger: Tree removal, mechanical and chemical woody vegetation suppression, tillage, introduce annual or perennial forage species.
Slow Variables: Increase production and management of forage species.
Thresholds: Changes in soil properties such as structure, organic matter, and nutrient cycling as well as changes in type and frequency of disturbance.
