Ecological dynamics

The information in this Ecological Site Description, including the state-and-transition model (STM), was developed based on historical data, current field data, professional experience, and a review of the scientific literature. As a result, all possible scenarios or plant species may not be included. Key indicator plant species, disturbances, and ecological processes are described to inform land management decisions.

The MLRA lies within the transition zone between the eastern deciduous forests and the tallgrass prairies. The heterogeneous topography of the area results in variable microclimates and fuel matrices that in turn are able to support prairies, savannas, woodlands, and forests. Sandy Floodplain Forests form an aspect of this vegetative continuum. This ecological site occurs on floodplains on moderately well to excessively-drained soils. Species characteristic of this ecological site consist of hydrophytic woody and herbaceous vegetation.

Flooding is the dominant disturbance factor in Sandy Floodplain Forests. Seasonal flooding occurs every one to two years, and flooding can persist up to 30 days. Floodwaters are fast, and the receding water deposits sediments and debris along the forest floor. Less frequent major and extreme floods result in shifts in the plant community, from early-successional communities with small trees and saplings forming open canopies to late-successional communities with large trees and closed canopies.

Today, many Sandy Floodplain Forests have been reduced as a result of conversion to pasture. A few sites have been cleared and drained for agricultural production. Remnant sites have been degraded due to significant changes to the natural hydrologic regime and water quality in the watershed. The state-and-transition model that follows provides a detailed description of each state, community phase, pathway, and transition. This model is based on available experimental research, field observations, literature reviews, professional consensus, and interpretations.

STATE 1 – REFERENCE STATE

The reference plant community is categorized as a floodplain forest community, dominated by hydrophytic woody and herbaceous vegetation. The three community phases within the reference state are dependent on a regular flood regime. The amount and duration of flooding alters species composition, cover, and extent.

Community Phase 1.1 Silver Maple – American Elm/Riverbank Grape/Whitegrass – Virginia Wildrye – Sites in this reference community phase are a closed canopy forest (80 to 100 percent cover) dominated by silver maple and American elm, with sub-dominants including eastern cottonwood, green ash, slippery elm, boxelder, and common hackberry. Trees are large (21 to 33-inch DBH) and range in height from 30 to over 80 feet tall (LANDFIRE 2009). Climbing vines, especially riverbank grape and bristly greenbriar (Smilax tamnoides L.), can be common. Whitegrass and Virginia wildrye are the dominant herbaceous species, but other species that can be encountered include sweet woodreed (Cinna arundinacea L.), Canadian clearweed (Pilea pumila (L.) A. Gray), Canadian woodnettle (Laportea canadensis (L.) Weddell), and fowl mannagrass (Glyceria striata (Lam.) Hitchc.). Average flood events will likely maintain this phase, but a major or extreme scouring event that removes some to all of the overstory will shift the community to phase 1.3 or 1.2.

Pathway 1.1A – Extreme flood event that removes the overstory.

Pathway 1.1B – Major flood event that reduces the overstory.

Community Phase 1.2 Black Willow/Virginia Wildrye – Devil’s Beggartick – This reference community phase represents a plant community in recovery from an extreme flood event that reduces the overstory canopy. Black willow becomes an important, early-successional woody species to establish on the recently cleared sites (Tesky 1992). Silver maple and American elm saplings can be present. The ground layer is generally sparse with mostly disturbance-tolerant species present, including Virginia wildrye and devil’s beggartick (Bidens frondosa L.). This community phase occurs from the time of disturbance to approximately 20 years (LANDFIRE 2009). Average flood events will slowly shift this community to phase 1.3.

Pathway 1.2A – Natural succession as a result of sediment accumulation from regular flooding.

Community Phase 1.3 Silver Maple/Black Willow/Virginia Wildrye – This reference community phase represents a mid-successional plant community phase. The tree canopy matures out of the sapling phase, with tree size class increasing to medium (9 to 21-inch DBH), cover increasing up to 80 percent, and heights reaching up to 30 feet. Black willow can still be present in the shrub layer, and the herbaceous layer remains sparse. Average flood events will slowly shift this community to phase 1.1 after approximately 60 years (LANDFIRE 2009)

Pathway 1.3A – Natural succession as a result of sediment accumulation from continuous flooding.

Pathway 1.3B – Major flood event that reduces the overstory.

Transition 1A – Altered hydrology throughout the watershed transitions the site to the hydrologically-altered state (2).

Transition 1B – Woody species removal and cultural treatments to enhance forage quality and yield transition the site to the forage state (3).

Transition 1C – Woody species removal, tillage, seeding of agricultural crops, and non-selective herbicide transition the site to the cropland state (4).


STATE 2 – HYDROLOGICALLY-ALTERED STATE

Agricultural tile drainage, stream channelization, and levee construction in hydrologically-connected waters have drastically changed the natural hydrologic regime of Sandy Floodplain Forests. In addition, increased amounts of precipitation and intensity have amplified flooding events (Pryor et al. 2014). This has resulted in a type conversion from the species-rich forest to a ruderal floodplain forest state. In addition, exotic species have encroached and continuously spread, reducing native diversity and ecosystem stability (Eggers and Reed 2015).

Community Phase 2.1 Silver Maple – Boxelder/Common Hackberry – Black Walnut/Creeping Jenny – This community phase represents a shift in plant community composition as a result of an altered hydrologic regime. Silver maple is still dominant, but the ruderal boxelder can begin to co-dominate. A reduced flooding frequency from stream channelization and water control structures allows other species to become prominent in the canopy composition including common hackberry, black walnut (Juglans nigra L.), honeylocust (Gleditsia triacanthos L.) and bitternut hickory (Carya cordiformis (Wangenh.) K. Koch). The bare soil conditions that result from flooding allow non-native species – such as Creeping jenny (Lysimachia nummularia L.) – to rapidly colonize and expand in the understory.

Pathway 2.1A – Continuing hydrologic alterations within the watershed.

Community Phase 2.2 Common Hackberry – Black Walnut/Multiflora Rose – Roughleaf Dogwood/Creeping Jenny – This community phase represents persisting changes to the natural hydrology of the watershed. The overstory canopy continues to shift, oftentimes becoming dominated by common hackberry and black walnut. Multiflora rose (Rosa multiflora L.) and roughleaf dogwood (Cornus drummondii C.A. Mey) are common in the shrub layer.

Transition 2A – Woody species removal and cultural treatments to enhance forage quality and yield transition the site to the forage state (3).

Transition 2B – Woody species removal, tillage, seeding of agricultural crops, and non-selective herbicide transition the site to the cropland state (4).

Restoration 2A – Site preparation, tree planting, timber stand improvement, non-native species control, and water control structures installed to improve and regulate hydrology transition this site to the reconstructed forest state (5).


STATE 3 – FORAGE STATE

The forage state arises when the site is converted to a farming system that emphasizes domestic livestock production, known as grassland agriculture. Fire suppression, periodic cultural treatments (e.g., clipping, drainage, soil amendment applications, planting new species and/or cultivars, mechanical harvesting) and grazing by domesticated livestock transition and maintain this state (USDA-NRCS 2003). Early settlers seeded non-native species, as smooth brome (Bromus inermis Leyss.) and Kentucky bluegrass (Poa pratensis L.), to help extend the grazing season (Smith 1998). Over time, as lands were continuously harvested or grazed by herds of cattle, these species were able to spread and expand across the landscape, reducing the native species diversity and ecological function.

Community Phase 3.1 Hayfield – Sites in this community phase consist of forage plants that are planted and mechanically harvested. Mechanical harvesting removes a significant portion of the aboveground biomass and nutrients that feed the soil microorganisms (Franzluebbers et al. 2000; USDA-NRCS 2003). As a result, soil biology is reduced leading to decreases in nutrient uptake by plants, soil organic matter, and soil aggregation. Frequent biomass removal can also reduce the site’s carbon sequestration capacity (Skinner 2008).

Pathway 3.1A – Mechanical harvesting is replaced with domestic livestock utilizing continuous grazing.

Pathway 3.1B – Mechanical harvesting is replaced with domestic livestock utilizing rotational grazing.

Community Phase 3.2 Continuous Pastured Grazing System – This community phase is characterized by continuous grazing where domestic livestock graze a pasture for the entire season. Depending on stocking density, this can result in lower forage quality and productivity, weed invasions, and uneven pasture use. Continuous grazing can also increase the amount of bare ground and erosion and reduce soil organic matter, cation exchange capacity, water-holding capacity, and nutrient availability and retention (Bharati et al. 2002; Leake et al. 2004; Teague et al. 2011). Smooth brome, Kentucky bluegrass, and white clover (Trifolium repens L.) are common pasture species used in this phase. Their tolerance to continuous grazing has allowed these species to dominate, sometimes completely excluding the native vegetation.

Pathway 3.2A – Domestic livestock are removed and mechanical harvesting is implemented.

Pathway 3.2B – Rotational grazing replaces continuous grazing.

Community Phase 3.3 Rest-Rotation Pastured Grazing System – This community phase is characterized by rotational grazing where the pasture has been subdivided into several smaller paddocks. Through the development of a grazing plan, livestock utilize one or a few paddocks, while the remaining area is rested allowing plants to restore vigor and energy reserves, deepen root systems, develop seeds, as well as allow seedling establishment (Undersander et al. 2002; USDA-NRCS 2003). Rest-rotation pastured grazing systems include deferred rotation, rest rotation, high intensity – low frequency, and short duration methods. Vegetation is generally more diverse and can include orchardgrass (Dactylis glomerata L.), timothy (Phleum pretense L.), red clover (Trifolium pratense L.), and alfalfa (Medicago sativa L.). The addition of native prairie species can further bolster plant diversity and, in turn, soil function. This community phase promotes numerous ecosystem benefits including increasing biodiversity, preventing soil erosion, maintaining and enhancing soil quality, sequestering atmospheric carbon, and improving water yield and quality (USDA-NRCS 2003).

Pathway 3.3A – Continuous grazing replaces rotational grazing.

Pathway 3.3B – Domestic livestock are removed and mechanical harvesting is implemented.

Transition 3A – Land is abandoned and left fallow; natural succession by opportunistic species transition this site the hydrologically-altered state (2).

Transition 3B – Tillage, seeding of agricultural crops, and non-selective herbicide transition the site to the cropland state (4).

Restoration 3A – Site preparation, tree planting, timber stand improvement, non-native species control, and water control structures installed to improve and regulate hydrology transition this site to the reconstructed forest state (5).


STATE 4 – CROPLAND STATE

The Midwest is well-known for its highly-productive agricultural soils, and as a result, much of the MLRA has been converted to cropland, including portions of this ecological site. The continuous use of tillage, row-crop planting, and chemicals (i.e., herbicides, fertilizers, etc.) has effectively eliminated the reference community and many of its natural ecological functions in favor of crop production. Corn (Zea mays L.) and soybeans (Glycine max (L.) Merr.) are the dominant crops for the site. These areas are likely to remain in crop production for the foreseeable future.

Community Phase 4.1 Conventional Tillage Field – Sites in this community phase typically consist of monoculture row-cropping maintained by conventional tillage practices. They are cropped in either continuous corn or corn-soybean rotations. The frequent use of deep tillage, low crop diversity, and bare soil conditions during the non-growing season negatively impacts soil health. Under these practices, soil aggregation is reduced or destroyed, soil organic matter is reduced, erosion and runoff are increased, and infiltration is decreased, which can ultimately lead to undesirable changes in the hydrology of the watershed (Tomer et al. 2005).

Pathway 4.1A – Tillage operations are greatly reduced, crop rotation occurs on a regular schedule, and crop residue is allowed to remain on the soil surface.

Pathway 4.1B – Tillage operations are greatly reduced or eliminated, crop rotation is either reduced or eliminated, and crop residue is allowed to remain on the soil surface, and cover crops are implemented to prevent soil erosion.

Community Phase 4.2 Conservation Tillage Field – This community phase is characterized by rotational crop production that utilizes various conservation tillage methods to promote soil health and reduce erosion. Conservation tillage methods include strip-till, ridge-till, vertical-till, or no-till planting systems. Strip-till keeps seedbed preparation to narrow bands less than one-third the width of the row where crop residue and soil consolidation are left undisturbed in-between seedbed areas. Strip-till planting may be completed in the fall and nutrient application either occurs simultaneously or at the time of planting. Ridge-till uses specialized equipment to create ridges in the seedbed and vegetative residue is left on the surface in between the ridges. Weeds are controlled with herbicides and/or cultivation, seedbed ridges are rebuilt during cultivation, and soils are left undisturbed from harvest to planting. Vertical-till systems employ machinery that lightly tills the soil and cuts up crop residue, mixing some of the residue into the top few inches of the soil while leaving a large portion on the surface. No-till management is the most conservative, disturbing soils only at the time of planting and fertilizer application. Compared to conventional tillage systems, conservation tillage methods can reduce soil erosion, increase organic matter and water availability, improve water quality, and reduce soil compaction.

Pathway 4.2A – Intensive tillage is utilized and monoculture row-cropping is established.

Pathway 4.2B – Cover crops are implemented to prevent soil erosion.

Community Phase 4.3 Conservation Tillage with Cover Crop Field – This condition applies conservation tillage methods as described above as well as adds cover crop practices. Cover crops typically include nitrogen-fixing species (e.g., legumes), small grains (e.g., rye, wheat, oats), or forage covers (e.g., turnips, radishes, rapeseed). The addition of cover crops not only adds plant diversity but also promotes soil health by reducing soil erosion, limiting nitrogen leaching, suppressing weeds, increasing soil organic matter, and improving the overall soil. In the case of small grain cover crops, surface cover and water infiltration are increased, while forage covers can be used to graze livestock or support local wildlife. Of the three community phases for this state, this phase promotes the greatest soil sustainability and improves ecological functioning within a cropland system.

Pathway 4.3A – Cover crop practices are abandoned.

Pathway 4.3B – Intensive tillage is utilized, cover crops practices are abandoned, monoculture row-cropping is established, and crop rotation is reduced or eliminated.

Transition 4A – Land abandonment transitions the site to the hydrologically-altered state (2).

Transition 4B – Cultural treatments to enhance forage quality and yield transition the site to the forage state (3).

Restoration 4A – Site preparation, tree planting, timber stand improvement, non-native species control, and water control structures installed to improve and regulate hydrology transition this site to the reconstructed forest state (5).


STATE 5 – RECONSTRUCTED FLOODPLAIN FOREST STATE

The combination of natural and anthropogenic disturbances occurring today has resulted in numerous ecosystem health issues, and restoration back to the historic reference state may not be possible. Many natural forest communities are being stressed by non-native diseases and pests, habitat fragmentation, permanent changes in hydrologic regimes, and overabundant deer populations on top of naturally-occurring disturbances (severe weather and native pests) (Flickinger 2010). However, these habitats provide multiple ecosystem services including carbon sequestration; clean air and water; soil conservation; biodiversity support; wildlife habitat; as well as a variety of cultural activities (e.g., hiking, hunting) (Millennium Ecosystem Assessment 2005; Flickinger 2010). Therefore, conservation of floodplain forests should still be pursued. Habitat reconstructions are an important tool for repairing natural ecological functioning and providing habitat protection for numerous species of Sandy Floodplain Forests. Therefore, ecological restoration should aim to aid the recovery of degraded, damaged, or destroyed ecosystems. A successful restoration will have the ability to structurally and functionally sustain itself, demonstrate resilience to the ranges of stress and disturbance, and create and maintain positive biotic and abiotic interactions (SER 2002). The reconstructed forest state is the result of a long-term commitment involving a multi-step, adaptive management process.

Community Phase 5.1 Early Successional Reconstructed Forest – This community phase represents the early community assembly from forest reconstruction. It is highly dependent on the current condition of the site based on past and current land management actions, invasive species, and proximity to land populated with non-native pests and diseases. Therefore, no two sites will have the same early successional composition. Technical forestry assistance should be sought to develop suitable conservation management plans.

Pathway 5.1A – Application of stand improvement practices in line with a developed management plan.

Community Phase 5.2 Late Successional Reconstructed Forest – Appropriately timed management practices (e.g. forest stand improvement, continuing integrated pest management) applied to the early successional community phase can help increase the stand maturity, pushing the site into a late successional community phase over time. A late successional reconstructed forest will have an uneven-aged, closed canopy and a well-developed understory.

Pathway 5.2A – Reconstruction experiences a setback from extreme weather event or improper timing of management actions.

Transition 5A – Removal of water control structures and unmanaged invasive species populations transition this site to the hydrologically-altered state (2).

Transition 5B – Tree removal and cultural treatments to enhance forage quality and yield transition the site to the forage state (3).

Transition 5C – Tree removal, tillage, seeding of agricultural crops, and non-selective herbicide transition this site to the cropland state (4).