Ecological dynamics
This ecological site occurs on moderately steep to steep backslopes throughout portions of the northern section of Crowley’s Ridge. Landscape position coupled with well drained, droughty soils directly influence the plant types and productivity of the area. Unlike the prevailing soils to the south, which are mainly deep loess, a significant portion of the area consists of a complex distribution of thick loess (> 4 feet), thin loess (< 4 feet), and loamy-skeletal material that is mainly comprised of surface sand and gravel. This complexity of the physical environment is clearly expressed in plant community differences.
Reconnaissance of this site suggests that areas where a loess cap is thickest, a mixed oak – hickory association is often supported. Canopy components may vary by stand but in general, species include southern red oak, black oak, post oak, with white oak and northern red oak occurring on moist sites, especially protected aspects (i.e., northwest- to east-facing slopes). Hickories typically consist of shagbark, mockernut, pignut, and black, the latter occurring on drier sites. Where loess deposits are thin, the community shifts to a drier association with a greater concentration of post oak, black hickory, and an entrance or increased presence of shortleaf pine and blackjack oak. This association is most pronounced and developed on exposed aspects (i.e., southeast- to west-facing slopes). The relative abundance or dominance of community components may vary by stand with some sites dominated by oaks and yet others by shortleaf pine. Land use history of local sites likely have an important influence on composition of many stands. Within this complex mosaic of soils, the lower slopes (e.g., footslopes) consist of deep colluvium – the results of past erosion. The protected, moist conditions of the footslopes often support a higher concentration of beech, maple, tuliptree, basswood, and walnut.
The pre-settlement vegetation of Crowley’s Ridge was projected by Clark et al. (1974), which was drawn from the journals of early naturalists and published state geologic reports (e.g., Call, 1891). For the portion of the Ridge associated with this site, much of the area was classed as an Oak – Hickory – Pine forest with potential overlap with a predominantly Mixed Oak – Hickory type. Today, vestiges of these vegetation types occur in scattered locations. One likely difference between the pre-settlement communities and current conditions is reflected in structural characteristics. The pre-settlement plant communities on the drier slopes were very likely open woodlands where fire was a critical and recurring disturbance factor. Many fires likely extended onto the upper portions of the moist, protected slopes. However, those areas likely remained somewhat protected given their occurrence in “fire shadows” (Nelson, 2005) and may have functioned as natural fire breaks. The moist lower slopes likely persisted under forest conditions (i.e., canopy closure greater than 75 percent), artifacts of a fire-sheltered environment.
Once settlement commenced, land uses and habitat alteration were extensive. Any location that could grow crops was farmed. Much of the area was either converted to pasture or remained in timber and repeatedly logged. With the advent of fire suppression, regrowth of formerly cutover land was often overcrowded and productivity suppressed. Today, the major land uses continue to be pastureland and forestry.
Following this narrative, a “provisional” state and transition model is provided that includes the “perceived” reference state and several alternative (or altered) vegetation states that have been observed and/or projected for this ecological site. This model is based on limited inventories, literature, expert knowledge, and interpretations. Plant communities will differ across MLRA 134 due to natural variability in climate, soils, and physiography. Depending on objectives, the reference plant community may not necessarily be the management goal.
The environmental and biological characteristics of this site are complex and dynamic. As such, the following diagram suggests pathways that the vegetation on this site might take, given that the modal concepts of climate and soils are met within an area of interest. Specific locations with unique soils and disturbance histories may have alternate pathways that are not represented in the model. This information is intended to show the possibilities within a given set of circumstances and represents the initial steps toward developing a defensible description and model. The model and associated information are subject to change as knowledge increases and new information is garnered. This is an iterative process. Most importantly, local and/or state professional guidance should always be sought before pursuing a treatment scenario.
State 1
Old Growth Woodland and Forest
The pre-settlement plant community of this ecological site was largely removed more than 150 years ago, and there are no extant examples remaining. However, inferences over the structure and dynamics of that system are drawn based on landscape position, soils, and existing community components.
This site is distributed across a highly dissected terrain and accordingly, encompasses many complexities including the presence/absence of loess; varying loess depths, where present; exposed vs. protected aspects; and a pronounced moisture gradient from upper slopes to footslope positions. Reference conditions for this site vary naturally with respect to those physical differences and includes several distinct natural communities or associations.
Two community phases are recognized for the reference state and they are distinguished from one another mainly by succession and disturbance type, size, and frequency.
Community 1.1
Dry-Mesic Mixed Oak – Hickory – Shortleaf Pine Woodland and Forest
The dominant species that occur over the distribution of this site are highly varied and directly influenced by soil type, aspect, and landscape position. A large proportion of the site was likely influenced by periodic fire. As a whole, the system may be classed as fire-adapted (NatureServe, 2011). However, certain positions and locations such as moist footslopes and north-facing slopes may have developed full, overlapping canopies and functioned as natural fire breaks. This community phase is so named to include the broad compositional and structural variation over the distribution of this site.
Mid- to upper slope positions on exposed aspects likely supported woodland characteristics. Periodic fires helped to maintain an open to moderately open canopy and understory. On the driest sites, shortleaf pine was very likely the dominant species with associates consisting of post oak, southern red oak, blackjack oak, black oak, black hickory and an understory of lowbush blueberry, farkleberry, and aromatic sumac. Mid- to upper slopes on protected aspects likely supported an oak – hickory association that consisted of white oak, southern red oak, northern red oak, black oak, various hickories, black gum, and hophornbeam and dogwood as mid-story components. The lower slopes supported the largest trees and highest canopy coverage. This protected environment supported greater diversity of canopy components including American beech, tuliptree, sweetgum, basswood, maple, walnut, white oak, northern red oak, cherrybark oak, hickory, and a fairly dense understory that consisted of American hornbeam, pawpaw, spicebush, and red buckeye.
Community 1.2
Dry-Mesic Mixed Oak – Hickory – Pine Dense Woodland/Forest
Many of the same canopy components of Phase 1 occurs in this phase with the possible exception of an increased presence of shade tolerant species entering the community. A major distinction is the crowding and encroachment of an expanding understory into higher strata of the woodland profile. Overall, this community phase supports a greater density or cover of woody vegetation at most all height strata or classes. The herbaceous ground cover is generally the most affected level of the community due to higher shade and loss of growing space.
Pathway 1.1A
Community 1.1 to 1.2
This pathway represents a decrease in disturbance frequency leading to a more closed, late development system. Overall, disturbance is light, infrequent, and localized – the result of single tree senescence or small group windthrow and a suppressed fire return interval.
Pathway 1.2A
Community 1.2 to 1.1
This pathway involves an increase in disturbance. Mixed severity fire is anticipated to thin this community back to Phase 1.1. Additional disturbances include larger gap- to incomplete stand-scale openings due to wind, ice, and forest management (e.g., group selection, basal area reductions).
State 2
Post Large-scale Disturbance Forest State
This state is characterized by the regeneration or regrowth of a pre-existing forest stand following a major, stand-replacing disturbance. Scale of the disturbance is at the stand level and is greater than one acre (Johnson et al., 2009). Potential disturbances include catastrophic windstorms, severe fire, insect outbreaks, silvicultural clearcuts, and particularly destructive ice storms. The resulting, even-aged stand (or single-cohort) is set on a new course of development, which is highly dependent upon several critical factors including: the composition and structure of the stand prior to the disturbance; the degree or intensity of the disturbance; size and configuration of the disturbed area; and distance to seed sources.
Composition and condition of the stand prior to a major disturbance may dictate, in large part, future composition of the regenerating stand. Although colonization by new species is expected soon after the disturbance, many of the pre-existing overstory components are anticipated to occupy position in the new, developing stand – their presence arising mainly from stump or root sprouts, advance regeneration, and germination from the seed bank (Oliver and Larson, 1990).
If the intensity of the disturbance only removed the overstory and damage to the understory strata was light, then understory components of advance regeneration may proliferate in the new opening. This may be a desired condition if managing for an oak shelterwood harvest and subsequent oak recruitment. However, this scenario is particularly problematic in high-graded stands.
Community 2.1
Woodland/Forest Regrowth
Soon after overstory removal, numerous species may colonize large openings and influence the dynamics of the site. Initial colonizers are often forbs, graminoids, and vines that may have existed in the seed bank, were forest floor components prior to disturbance, or transported into the site via wind and/or animals. Early successional or pioneer species may include winged elm, sumac, greenbrier, grapevine, blackberry, and various graminoids. Overstory species anticipated to occur during the stand-initiation stage include post oak, southern red oak, black oak, shortleaf pine, and various hickories on the driest sites and white oak, northern red oak, hickory, beech, maple on moist, protected sites. Composition of the young stand will vary dramatically if the disturbance is a well-designed and implemented shelterwood harvest that favors the advancement of an established oak understory.
For stands that were highly altered prior to the disturbance (e.g., high-graded), intensive management may be necessary in order to establish a desired composition. Management actions may include controlling undesirable species mechanically and chemically and planting the desired components.
State 3
High-graded/Grazed Forest
Forests in this state have undergone repeated select harvests over time. Actions leading to this condition consist of removing the biggest and best trees of the most desirable species and leaving low-quality trees (damaged and deformed) and undesirable species. This action, conducted repeatedly, can cause tremendous shifts in species composition and can decrease the vigor and health of the residual stand. Without implementing carefully prescribed management actions, species composition of extreme high-graded stands may remain in a highly altered condition for many decades, even after large, stand-replacing disturbances resets “successional opportunity.”
Today, this vegetation state probably represents the conditions of many forest stands throughout the distribution of this site. Local stands in which desirable species such as oaks and shortleaf pine were repeatedly targeted often results in sites with proportionally more hickory.
Because “overgrazed woods” often consists of components very similar to high-graded stands, uncontrolled livestock access to forests is also included in this state. This does not take into account carefully prescribed and/or managed forms of forest grazing (e.g., agroforestry or silvopasture), which generally has a mutual goal of providing quality forage and productive forest management. The conditions considered and represented here are the extreme cases of long-term forest grazing; this form of uncontrolled access has been referred to as “turning livestock into the woods” (Brantly, 2014).
A single community phase is selected to represent the breadth of conditions that may be anticipated in stands having been high-graded and uncontrolled access by livestock.
Community 3.1
Hickory-Oak/Hophornbeam
High-graded stands generally consist of a paucity of oaks. Species typically left or avoided during harvests often include hickory and practically the entire understory. This has resulted in canopies largely comprised of the preceding species along with a dense understory of hophornbeam and “scrub oak” or undesirable species such as post oak and blackjack oak. Noticeable characteristics of this condition are a conspicuous reduction of more merchantable oaks and other valuable hardwoods.
The most palatable forage of a forest stand is typically the herbaceous understory, which is targeted first. The combined effects of trampling, browsing woody plants, and foraging on the herbaceous layer often results in a high percentage of bare soil, exposed roots, and an open understory. Furthermore, overstory trees occurring in stands with high livestock traffic grow more slowly over time (Johnson, 1952).
State 4
Timber Management
This state represents the breadth of forest management activities on this site. Various management or silvicultural methods can lead to very different structural and compositional results within a managed stand. The range of methods are diverse and include even-aged (e.g., clearcut and shelterwood) and uneven-aged (single tree, diameter-limit, basal area, group selection, etc.) approaches. Included within these approaches is an option to use disturbance mechanisms (e.g., fire, TSI, etc.) to reduce competition and achieve maximum growth potential of the desired species. Inherently, these various approaches result in different community or “management phases” and possibly alternate states. The decision to represent these varying approaches and management results into a single state and phase at this time hinges on the need for additional information in order to formulate definitive pathways, management actions, and community responses. Forthcoming inventories and description iterations of this site will provide more detail on this state and associated management phases.
Community 4.1
Mixed Oak – Pine (Various)
Some of the most desirable timber consists of oak and tall mixed hardwoods on protected sites and shortleaf pine on the drier sites. Depending on the desired end product, management activities will differ. Management for oak dominant stands may be achieved by shelterwood and/or seed tree approaches. Managing for shortleaf pine may only require timber stand improvement methods where pine is currently dominant, or artificial regeneration may be called for where other hardwoods predominate. The droughty portions of this site respond well to fire, and low intensity ground fires on a frequent return interval can be an effective tool for reducing competition and potentially enhancing production of individual trees. Conversely, competition intensifies from various hardwoods on more moist sites and managing for oak can be problematic (see Johnson et al., 2009).
The complex distribution of soils on this site may affect the response of a given stand. For this very reason, consideration of site factors and conditions should be applied into the decision-making process well before management begins. Finding the appropriate approach for a given stand and environment necessitates close consultation with trained, experienced, and knowledgeable forestry professionals. It is strongly urged and advised that professional guidance be secured and a well-designed silvicultural plan developed in advance of any work conducted.
State 5
Grassland/Pastureland
This state is representative of sites that have been converted to and maintained in pasture and forage cropland, typically a grass – legume mixture. For pastureland, planning or prescribing the intensity, frequency, timing, and duration of grazing can help maintain desirable forage mixtures at sufficient density and vigor (USDA-NRCS, 2010; Green et al., 2006). Overgrazed pastures can lead to soil compaction and numerous bare spots, which may then become focal points of accelerated erosion and colonization sites of undesirable plants or weeds.
Establishing an effective pasture management program can help minimize the rate of weed establishment and assist in maintaining vigorous growth of desired forage. An effective pasture management program includes: selecting well-adapted grass and/or legume species that will grow and establish rapidly; maintaining proper soil pH and fertility levels; using controlled grazing practices; mowing at proper timing and stage of maturity; allowing new seedings to become well established before use; and renovating pastures when needed (Rhodes et al., 2005; Green et al., 2006). It is strongly advised that consultation with State Grazing Land Specialists and District Conservationists at local NRCS Service Centers be sought when assistance is needed in developing management recommendations or prescribed grazing practices.
Community 5.1
Select Forage/Species Mixture
This community phase represents commonly planted forage species on pasturelands, haylands, and open grasslands. The suite of plants established on any given site may vary considerably depending upon purpose, management goals, usage, and soils. Most systems include a mixture of grasses and legumes that provide forage throughout the growing season. Cool season forage may include tall fescue (Schedonorus arundinaceus), orchardgrass (Dactylis glomerata), white clover (Trifolium repens), and red clover (T. pratense), and warm season forage often consists of bermudagrass (Cynodon dactylon), bahiagrass (Paspalum notatum), and annual lespedeza (Kummerowia spp.). Several additional plants and/or species combinations may be desired depending on the objectives and management approaches and especially, local soils.
Should active management (and grazing) of the pastureland be halted, this phase will transition to “old field” conditions, which is the transitional period between a predominantly open, herbaceous field and the brushy stage of a newly initiated stand of trees.
Transition T1A
State 1 to 2
This pathway represents a large-scale, stand replacing disturbance, which may be caused by a catastrophic windstorm (e.g., straight-line winds, tornado), ice storm, severe fire, or a silvicultural clearcut. For this stressor to occur, most or all of the overstory must be removed or destroyed. A few residual trees may persist, but overall, the disturbance must be intensive enough, at least one acre and larger (Johnson et al., 2009), that a new, even-aged stand is created.
Transition T1B
State 1 to 3
Repeated selective harvesting or high-grading over time can cause shifts in species composition, structure, and overall health of affected stands. High-grading occurs when the most desirable trees of select species are repeatedly removed leaving behind inferior, low quality stems and undesirable species. This transition also includes uncontrolled access by livestock and impacts from sustained, selective grazing and browsing.
Transition T1C
State 1 to 4
This pathway consists of prescribed silvicultural activities specifically designed to meet stand compositional and production objectives.
Transition T1D
State 1 to 5
Actions required to convert forests to pasture or forage production include forest clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants.
Restoration pathway R2A
State 2 to 1
This pathway represents a return to reference conditions through natural succession, if the disturbance occurred within a reference community.
Transition T2A
State 2 to 4
This pathway represents the development of an even-aged stand that is prescribed to meet compositional and production objectives.
Transition T2B
State 2 to 5
Pathway represents a conversion of the emerging stand to pastureland or hayland. Actions required include forest clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants.
Restoration pathway R3A
State 3 to 2
This pathway represents a large-scale, stand replacing disturbance, which may be caused by a catastrophic windstorm (e.g., straight-line winds, tornado), ice storm, severe fire, landslide, or a silvicultural clearcut.
Transition T3A
State 3 to 5
Actions include forest clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants.
Restoration pathway R4A
State 4 to 1
Natural succession over a period of time coupled with disturbance such as low intensity (and possibly mixed severity fire) may transition a former timber-managed stand to one supporting reference conditions. Some question remains whether a return to reference conditions will occur in every situation, especially since some components may have been selectively culled from the stand. Management activities to aide recovery may include exotic species control and silvicultural treatment.
Restoration pathway R4B
State 4 to 2
This pathway represents a large-scale, stand-initiating disturbance, which effectively removes most or all of the pre-existing overstory. Disturbances may include a catastrophic windstorm, severe wildfire, and silvicultural management (even-aged).
Transition T4A
State 4 to 3
Repeated selective harvesting or high-grading of stands over time can cause shifts in species composition, structure, and overall health of affected stands. This transition also includes uncontrolled access by livestock and impacts from sustained, selective grazing and browsing. Impacts from continual grazing and uncontrolled access can result in the removal of palatable understory components, alteration of species composition in current and future stands, conditions for exotic plant invasions, and soil compaction and erosion.
Transition T4B
State 4 to 5
Actions include forest clearing, stump removal, herbicide application, seedbed preparation, and the establishment of desired plants.
Restoration pathway R5A
State 5 to 1
This pathway represents natural succession back to perceived reference conditions. The period required for this transition to take place likely varies by location and is dependent upon local site conditions. LANDFIRE models (2008) suggest that over 60 years is required for a return to a late development community and this pathway is highly dependent upon species present in the developing stand in addition to the appropriate level and type of disturbance (e.g., fire return interval). Significant efforts may be required before a return to reference conditions is achieved (e.g., exotic species control, appropriate intensity and return interval of fire, potential artificial regeneration of community components, etc.).
Restoration pathway R5B
State 5 to 4
This pathway represents prescribed management strategies for transitioning abandoned pastureland to managed woodland. Activities may include artificial regeneration of desired species; exotic species control; appropriate intensity and return interval of fire.
