Northern Deep Loess Summit

Description

The pre-settlement plant community of this ecological site was largely removed more than 150 years ago, and there are no extant examples of the former system. Based on projections from others, oaks were important components of that community (Hodges, 1995). Structural characteristics are open for debate but there are indications that the Loess Hills had an open physiognomy (see Heineke, 1987). It is possible that portions of this site supported open to moderately open woodland conditions with canopy coverage ranging from 30 to 75 percent. However, the natural fertility and high available water capacity of the deep loess soils of this site foster tremendous plant productivity. Without management actions (e.g., fire) to control vegetation growth, a closed-canopy forest develops rapidly on this site.

Following decades of land-use impacts and erosion, the plant community that returned in those areas initially set aside for protection 50 to 80 years ago (e.g., parks, natural areas, and refuges) are often comprised of a large oak component. Associates with oaks include a broad range of hardwoods that respond incredibly well on the fertile, moist soils of this site.

Two community phases are currently recognized within the reference state of this ecological site. They are distinguished from one another based on the degree of dominance by oak (Community Phase 1.1) and eventual replacement of oaks by shade tolerant species (Community Phase 1.2).

Submodel

Description

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 in size (Johnson et al., 2009). Potential types of disturbances include catastrophic windstorms, wildfire, landslides, 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 forest 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). This generality may fail depending upon the intensity of the disturbance and understory structure of the pre-existing stand. Of particular concern, oak regeneration, even in formerly oak-dominated stands, is particularly problematic on this site and may require additional measures before oak dominance is expressed in the new stand (see Beck and Hooper,
1985; Goelz and Meadows, 1995; Lockhart et al., 2010).

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 where repeated select cuttings ultimately favored dense concentrations and advancement of hophornbeam, American hornbeam, beech, and sugar maple throughout the understory. Overstory removal would ultimately favor proliferation of the preceding species, further complicating and impeding regeneration of a more diverse stand.

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Description

Forests in this state have undergone repeated select harvests over time. Actions leading to this condition consist of removing the largest 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, tuliptree, walnut, etc. were repeatedly targeted often results in sites with proportionally more hickory, maple, and beech. Stands where hickory was also targeted often support maple, hophornbeam, and disproportionate numbers of other components such as boxelder, hackberry, and sugarberry.

Because “overgrazed woods” often consists of components very similar to high-graded stands, uncontrolled livestock access to forests is also included in this state. It 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).

Forest stands that sustain heavy and frequent livestock traffic often have an open understory consisting of few herbaceous plants; low numbers of woody seedlings and shrubs; damaged tree roots; compacted soils; and varying levels of soil erosion. Composition of heavily grazed stands varies depending on the length of time grazing has occurred within the stand, the type(s) of livestock having access (hence, different grazing strategies), former forestry or logging practices, and conditions or composition of the forest prior to grazing.

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.

Submodel

Description

Three timber managed phases are included to represent the range of management options and associated outcomes, given their importance and interest by silviculturists, landowners, land managers, and industry. The level of management intensity, the density of oaks relative to other hardwoods, and the establishment of pine distinguish them. The first phase is an oak-centric management approach that promotes oak regeneration and production. Currently, the distribution of an oak-managed system is probably very rare and restricted due to the level of management commitment required for its development, maintenance, and perpetuation. The second phase represents a natural transition from an oak-managed system once specific management actions are relaxed. Incidentally, this phase also represents stands where even-aged methods (e.g., clearcut) and larger group selection harvests are conducted without oak-specific management actions (e.g., TSI, competitor control, oak shelterwood approach, etc.). The third and final phase represents the conversion to a pine monoculture (or plantation).

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Description

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.

Three community phases of this state are currently recognized. They differ in the level of grazing pressure and progression of natural succession should active management and/or grazing cease.

Submodel

Description

This state represents a return to forest conditions following the abandonment of pastureland/grassland and cropland management. The developmental stage of this state follows the “old field” condition and begins at canopy closure of the new forest stand. This initiates the stem exclusion period whereby establishment of additional canopy species becomes exceedingly difficult without active management (Oliver and Larson, 1990).

Composition of the resulting forest will vary considerably depending on the amount of time the site was previously managed; the intensity of former land use practices; the condition of the land prior to abandonment; and the source and distance of the nearest seed sources. Some pioneer species of the new stand may dominate early on but will be replaced by competitors within the community as the stand matures. Competitive interactions are intense at this stage.

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Description

Immediately upon settlement, the fertility of the soils led to rapid land clearing and crop production. Any ridgetop that was wide enough to pull a plow through was cultivated. Beyond subsistent crops, cotton became the cash crop of choice. After tremendous impacts were incurred upon the land, cotton was largely abandoned as a profitable commodity on this site. Today, crops that are often established include corn and soybean, mostly. Agriculture production is generally a minor state or land use on this site due to the narrowness of the ridgetops and the dissected landscape.

There are a few orchards that have been established on some of the ridges of the Loess Hills, but this too is relatively minor compared to other land use categories. Of the active orchards that have been observed, peach production may be among the most important.

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