Ecological dynamics
The Sandy Upland Savannas ecological site is primarily located in areas adjacent to the Big Woods region of Minnesota and along the central and southern rivers in MLRA 103. Natural fire disturbance was suppressed but not eliminated in these areas resulting in a savanna landscape. This site differs from the other upland savanna concepts in that it is typically a drier, less productive site. It is also confines to a more southerly extent, so therefore lacks aspen that is more dominant in the northern reaches of the savanna in MRLA 103.
The state and transition model (STM) consists of three states: Reference State, Tillage State, and the Degraded Oak Woodland State. The Reference State describes a dry to dry-mesic savanna with native grasses and scattered oaks. State 2 is the Tillage State which describes land transitioned to agricultural production. This is the most common state in MLRA 103 for this site. A few areas within this State have been reseeded to native warm season or cool-season grasses. State 3 is a Degraded Oak Woodland State in which disturbances have modified the plant community composition and structure. Lack of natural fire, unmanaged grazing, and invasive species are common triggers transitioning a site to State 3.
State 1
Reference State
The Sandy Upland Savannas ecological site reference state is a dry to dry-mesic savanna that exhibits a diversity of native grasses and forbs along with scattered oaks. Plant community structure and composition within the Reference State are variable and dependent upon the impacts of drought, grazing, and fire events. Depending upon disturbance regimes, woody species will vary in density and structure. Areas with frequent fire will trend toward a shrubby prairie. Longer fire return intervals will result in a mixed oak savanna. A long-term absence of fire will transition the site toward a dry woodland. Characteristic vegetation in the reference savanna state includes bur oak, northern pin oak, American hazelnut, leadplant, little bluestem, and porcupinegrass. High-quality, untilled areas of the Sandy Upland Savannas ecological site are uncommon in MLRA 103 as most sites have been transitioned to agricultural production.
Community 1.1
Reference Community
The Sandy Upland Savannas ecological site is characterized by a diversity of native grasses, forbs, and scattered oak trees. Common reference species include bur oak, northern red oak, American hazelnut, leadplant, little bluestem, porcupinegrass, and an array of forbs. The vegetative composition is influenced primarily by drought, grazing and fire.
State 2
Tillage State
Soil tillage is the primary mechanism to transition a site to the Tillage State. In this state, dynamic soil properties such as bulk density, structure, organic carbon content, and saturated hydraulic conductivity are altered by agricultural practices. Certain practices can mitigate the impacts of traditional agricultural practices on soil health. Conservation tillage minimizes soil disturbance and can improve soil structure and overall soil health. Corn or soybean plantings and a cover crop rotation can build soil structure, improve infiltration rates, reduce runoff and erosion, and protect water quality.
Some areas in this ecological site are not appropriate for intensive crop production due to slope. Where the gradient exceeds 20 percent row crop production is not feasible due to limitations on farm machinery.
A few areas within this ecological site have been tilled but seeded back to grass. Under conservation programs such as the NRCS Conservation Reserve Program (CRP), previously tilled areas have been converted to warm-season grasslands. Native forbs are commonly included in seed mixes to benefit wildlife and pollinators.
Cool-season grasses are also feasible. Species selection will depend on the landowner’s objectives and site specifics. Although these areas are not as diverse as the reference state, they still provide soil health and wildlife benefits.
Community 2.1
Tillage Community
The Tillage Community typically consists of intensively produced, traditional row crops on lower slope sites. Tillage and intentional plant establishment (crop seeding) are the primary triggers for this community. The most common crops are corn and soybeans on an annual rotation. Agriculture practices will be limited by slope. Many areas within this ecological site are not feasible for machinery as slopes range from 0% to over 40%. Dryness may also be a limiting factor.
Community 2.2
Seeded Grassland Community
The primary mechanism of change to this community is the seeding of desired grass species. Commercial vegetative seed mixes commonly include a variety of native grasses plus forbs to enhance wildlife habitat and to benefit native pollinators. This pathway is commonly triggered in conjunction with a conservation program such as the NRCS Conservation Reserve Program (CRP). The site is taken out of crop production and seeded with warm-season grasses to benefit wildlife, soil health, and water quality.
A few areas within this ecological site may be seeded to cool-season grasses. Numerous species may be planted depending on the landowner's objectives. Legumes, such as white clover and red clover, are commonly incorporated to improve forage nutrition.
Resilience management. Multiple resilience management practices may be needed after establishment of warm-season grasses. Examples include prescribed fire, brush management, and herbaceous weed treatment. Prescribed burning is utilized to reduce the extent of woody vegetation, reduce the buildup of dead plant material, and promote the regeneration of native grasses and forbs. Resilience management practices for cool-season grass sites include planned grazing, invasive plant management, and appropriate disturbance/harvest management. Managed grazing is also a practice on some sites that promotes plant community resilience.
Pathway 2.1A
Community 2.1 to 2.2
The mechanism of change is the seeding of grass species. Warm season or cool season grasses may be planted depending on the landowner's objectives. Warm season grasses may be established as part of a NRCS conservation program.
Forage and Biomass Planting |
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Pathway 2.2A
Community 2.2 to 2.1
The site is transitioned back to cropland through tillage..
State 3
Degraded Oak Woodland
This State is characterized by a disturbed and degraded woodland condition. Characteristics include the dominance of trees (no longer a true savanna community), the presence of invasive plant species, and a reduction in the diversity of native understory and shrub species. Oaks still generally dominant but are joined by a mix of hardwood species. Non-native plants, such as Kentucky bluegrass and common buckthorn, are often dominant the understory. As the tree and shrub density increases, the ground layer plant diversity decreases and transitions to more shade-tolerant species.
Community 3.1
Degraded Oak Woodland Community
This plant community exhibits and increase in woody species and invasive plants. Native plant diversity is decreasing. Tree species include oaks and mixed hardwoods. Due to the increasing shade levels, ground flora are transitioning to more shade-tolerant species. The community is no longer a savanna but transitioning to a woodland.
Transition T1A
State 1 to 2
The site is transitioned to agricultural production through tillage and seeding of desired crops.
Transition T1B
State 1 to 3
Transition mechanisms include absence of a natural fire regime, invasion of non-native plant species, and a continual increase in woody species. Native grassland plant diversity will decrease as the community transitions from a open savanna to a closed, shaded woodland.
Restoration pathway R3A
State 3 to 1
Restoration of the site to include non-native vegetation control, introduction of prescribed fire, establishment of desired native species.
Transition T3A
State 3 to 2
Site is transitioned to agricultural production via tillage and seeding of desired crops.