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Guideline S.4 Vegetation

Intent

To optimize the ecological function of project sites by restoring Minnesota’s native vegetation, protecting natural areas, conserving existing site features, and selecting vibrant and appropriate vegetation to ensure the optimum functioning of ecosystems.

Required Performance Criteria

Guidelines apply to all projects designated New Buildings and Major Renovations with site work site scope that includes an area of site disturbance that is greater than 3,000 s.f. OR Area of imperviousness (footprint of building plus site impervious area) renovated that is greater than 2,000 s.f.

A. New construction projects shall not select sites which contain any of the following:

      1. Prime farmland (as defined by the NRCS WSS).
      2. Farmland of state significance (as defined by the NRCS WSS).
      3. Former municipal, township, or county parkland.
      4. Former federally protected lands.
      5. Areas covered by a conservation easement.

Note: On areas under a conservation easement, the only allowed activity is restoration to the original NPC, per the DNR’s County Biological Survey (CBS).

B. The following tree conditions shall be established:

    1. Minimum combined trunk areas of all trees (including deciduous and coniferous) as evaluated at 10-year estimated maturity post construction and measured by calculating the trunk area at 4.5 ft. above the ground (i.e., DBH) for the site’s tree plant community. Tree trunk area must be at least:
      1. Tallgrass aspen parkland and savanna: 2 sq. ft. of trunk area per acre.
      2. Southern and southeastern hardwood deciduous: 4 sq. ft. of trunk area per acre.
      3. Northern deciduous: 3 sq. ft of trunk area per acre.
      4. Boreal conifers: 4 sq. ft. of trunk area per acre.
    2. Required minimum of tree diameter per acre as evaluated in DBH to trunk area at ten years maturity, and number of large, medium, and small trees needed to achieve this requirement:
      Type of Tree Plant CommunitySq. Ft. (144 sq. in./1 sq. ft.) Trunk Area Per AcreNumber of Large Trees Only (0.66 sq. ft. ea/12-in. DBH)Number of Medium Trees Only (0.39 sq. ft. ea/7-in. DBH)Number of Small Trees Only (0.20 sq. ft. ea/3-in. DBH)
      Prairie0000
      Tallgrass Aspen Parkland and Prairie Savanna 2-43-65-1110-20
      South & Southeast Hardwood Deciduous4-76-1111-1820-35
      Northern Deciduous3-65-108-1615-30
      Boreal Coniferous4-76-1111-1820-35
        1. Sample Ratios of Trunk Areas at DBH
      DBH InchesArea Square InchesArea Square Feet
      10"78 sq. in.0.55 sq. ft.
      15"177 sq. in.1.23 sq. ft.
      20"314 sq. in. 2.19 sq. ft.
      25"491 sq. in.3.41 sq. ft.
        1. Annual Tree Growth Diameter Increase in Inches DBH with trees planted at ~1-in. DBH/2.5-in. Caliper:

      Tree Type SizeAnnual Rate Increase in Inches of DBHDBH in Inches at Ten YearsArea of Trunk at Listed DBH in Square Inches at Ten YearsArea of Trunk at DBH in Square Feet at Ten Years
      Large>1"~11"95 sq. in.0.66 sq. ft.
      Medium>3/4"~8 1/2"57 sq. in.0.39 sq. ft.
      Small>1/2"~6"28 sq. in. 0.20 sq. ft.
    3. Adequate tree soil volumes should be achieved. Where trees are surrounded by hard surfaces (e.g., sidewalks, patios, driveways, car parks, plazas, parking islands), suspended pavement techniques, structural soils, or other comparable methods such as larger tree openings to provide adequate rootable soil volumes should be used. Minimum volume of rootable soil volume per tree is:
      1. Small trees (e.g., Serviceberry – Amelanchier): 400 cu. ft.
      2. Medium trees (e.g., Ironwood – Ostyra): 800 cu. ft.
      3. Large trees (e.g., Hackberry – Celtis): 1,200 cu. ft.

      If using structural soils, multiply the total soil volumes above by five to obtain equivalent volume of soil useable by the tree. If above soil volumes cannot be met, trees species requiring smaller soil volumes should be selected. Where applicable, suspended pavement or comparable methods should be utilized to allow tree roots under hard surfaces to access adjacent open space.

    4. Adequate tree diversity should be achieved to limit susceptibility of site to disease and increase ecological resilience: Tree genera of like form should be planted in large single species tree plantings, such as allees or formal groupings. For example, Kentucky coffeetree (Gymnocladus), honey locust (Gleditsia), and black locust (Robinia) are similar in form, structure, and leaf texture but are three different genera not susceptible to the same pests and diseases. The following numbers of tree generas should be achieved:
      1. Three genera on sites of fewer than 2 acres.
      2. Five genera or more on sites of 2 to 5 acres.
      3. Seven genera or more on sites of 5 to 10 acres.
      4. Nine genera or more on sites of 10 to 15 acres.
      5. Twelve genera or more on sites of 15 to 20 acres.
      6. Fifteen genera or more on sites of 20 to 40 acres.
      7. Eighteen genera or more on sites of 40 to 100 acres.
      8. Twenty genera or more for sites of greater than 100 acres.
    5. Tree planting requirements: At time of tree planting, the following criteria should be met:
      1. All soil/mulch/media covering trunk flare removed.
      2. Point of stem/root union exposed at original ground surface elevation (see UMN Extension).
      3. Caliper size of all trees limited to 2.5 in. at planting.
      4. All stem girdling roots (SGR) on trees rejected or removed (see UMN Extension).
      5. Metal baskets and burlap removed from balled-and-burlapped (B&B) root balls to 12 in. below soil level.
      6. Trees should not be planted deep in the planting hole to stabilize them.
      7. Mulch should not be placed against tree trunk deeper than 1-in. deep; tree stem/root union should be planted 1 to 3 in. higher than surrounding ground plane elevation.
      8. Newly planted trees should be watered at a rate of 1.5 gal. per caliper in. per 3 calendar days from May through September, at the following intervals. Watering bags are recommended.
          1. Year 1: At least every three days
          2. Year 2: At least weekly
          3. Year 3: At least every two weeks

        See soil section for acceptable drainage and bulk density rates for soils in planting areas.

      9. Crowns should not be pruned at planting to balance root and crown volumes.
      10. Broken branches should be pruned and removed to develop a single central leader. Codominant branches that exceed half of tree trunk diameter at branch/trunk attachment point should be removed.
      11. Trees in containers that are rootbound should be box cut (see UMN Extension).

      The following should be evaluated and implemented if feasible:

      1. Contracting growing trees for orders exceeding 20 trees total.
      2. Growing bare root stock in Missouri gravel bed nursery for half the growing season prior to planting out to create a large vigorous tree root system (see UMN Extension).
      3. Using arborist’s wood chips, mulch to a depth of up to 6 in. deep, over tree root systems but not against trunks. If trees are unstable in their planting hole reject trees or require one year of tree staking.
      4. Grade all landscaped areas to slope towards tree plantings

C. The vegetation selected shall be subject to the following and selected in coordination with the animal and vegetation requirements listed under S.1 and animal habitat requirements listed under S.5:

    1. Existing, noninvasive, nonnative vegetation should not be removed solely in order to achieve the amount of native vegetation required under S.1A.
    2. The selection of herbaceous plantings for prairies, wetlands, savannas, parklands, and forests shall use the methodology (steps 1–5) found in MnDOT’s Native Seed Mix Design for Roadsides (2014): www.dot.state.mn.us/environment/erosion/pdf/native-seed-mix-dm.pdf.
    3. The required strata are a ground layer less than 48 in. tall and a tree canopy greater than 78 in. tall.
    4. Keystone species shall be selected according to the following restoration goals:
      1. Where savanna, south and southeastern hardwood deciduous, and northern deciduous are being restored, one of the selected trees in the cohort population shall be included: burr oak (Quercus macrocarpa)
      2. Where prairie and savanna are being restored, one of the selected trees in the cohort population should be included: American hazelnut (Corylus americana) or beaked hazelnut (Corylus cornuta).
      3. Where prairie, tallgrass aspen parkland, and savanna are being restored, two of the selected grasses in cohort population should be included: dry/xeric grasses: little bluestem (Schizachurium scoparium) and side oats gramma (Bouteloua curtipendula); medium/mesic grasses: big bluestem (Andropogon gerardii) and Indian grass (Sorgastrum nutans); wet/hydric grasses: switch grass (Panicum virgatum) and prairie cord grass (Spartina pectinata).
      4. Where south and southeastern deciduous hardwood and northern deciduous and boreal conifers are being restored, one of the selected trees in the cohort population should be included: serviceberry (Amelanchier canadensis).
      5. Where boreal conifers are being restored, one of the selected trees in the cohort population should be included: white pine (Pinus strobus).
    5. The coefficient of conservancy for all B3 sites with wetland hydrology at planting must be greater than four as calculated by the floristic quality assessment (FQA) method (per Wilhelm 1977). In areas adjacent to water bodies or wetlands or rivers or streams, a series of exploratory holes 12 in. deep should be dug between April and November. If water appears and persists in the hole for more than two hours after excavation, an FQA must be performed.
    6. Invasive species on site should be determined using the Invasive Species County Weed Guideline. If the site does contain invasive species, a mitigation and maintenance plan as defined by the Minnesota Department of Agriculture should be created or implemented.
    7. All vegetation must be selected in accordance with the correct local USDA hardiness zones.

D. Pollinator friendly vegetation:

  1. Neonicotinoid-free sites: All project plantings must use a written chain of custody method to verify neonicotinoid-free claims. Reject plants that have been neonicotinoid treated, or that do not have a clear, verifiable chain of custody of being neonicotinoid-free. This requirement also applies to trees, shrubs, and vines.
  2. Site plantings should be selected so that at least 50% by quantity of all trees, shrubs, groundcovers, vines, and herbaceous perennials are insect pollinated, and rich in pollen and/or nectar.
  3. Blooming pollinator plants should be provided for all three seasons of blooms (spring, summer, fall), with at least two different species blooming during each season.
  4. Coincidently blooming pollinator plants should be clustered in large groupings to reduce expended energy of insect pollinators.
  5. Abundant human and natural structural enhancements should be provided for insect pollinators (e.g., dead tree snags, downed tree logs, sand baths, bee skeps, solitary beehives, mason bee houses, green roofs, and green walls).
  6. Cultivars with double and triple petal flowers that do not produce pollen or nectar should be minimized.

Note: This guideline has been developed in response to Minnesota Executive Order 16-07, which also outlines requirements of specific state agencies, departments, boards, and committees not listed here.

E. Achieve biomass target according to major ecosystem of site, as measured in biomass per area of vegetated site area, estimated at ten years post-occupancy according to the major ecosystem characterization from DNR:

    1. Prairie: 1.1 kg per square meter or 2.03 pounds per square yard.
    2. Tallgrass aspen parkland and savanna: 0.9 kg per square meter or 1.66 pounds per square yard.
    3. South and southeastern hardwood deciduous forest: 0.7 kg per square meter or 1.29 pounds per square yard.
    4. Northern deciduous and boreal conifer: 0.6 kg/per square meter or 1.11 pounds per square yard.

These biomass targets do not apply to the restoration of specialized NPCs installed pursuant to S.3K: Atypical Soils.

F. Site should be designed so that the entire site albedo is at least 0.25 (25%) as evaluated using the B3 Albedo Calculator.

Recommended Performance Criteria

  1. Use a diversity of native plants to express multiple design styles (do not exceed 500 of any single herbaceous perennial species or cultivar; 50 of any single shrub species or cultivar; 10 of any single tree species or cultivar). DNR’s 49 designated terrestrial invasive plants should not planted.
  2. Subject sites with existing NPCs should be protected from development, and DNR Heritage Division staff consulted for restoration of existing native plant areas.
  3. Achieve an entire site albedo of at least 0.3 (30%) as evaluated using the B3 Albedo Calculator.

In the Predesign and early design of the project, determine ideal spatial needs for existing or new development. Critical sites for preservation or restoration on the project site as defined by the B3 Guidelines should be identified, and the type of buildings and related infrastructure that will be required for the developed areas and their spatial requirements should be determined. After a site has been selected, create potential spatial footprints that preserve any critical sites identified during the Predesign phase.

Select a site where the proposed building and infrastructure will have minimal disturbance on the existing vegetation and the supporting soil and hydrologic conditions. Areas of vegetation or high quality areas for restoration should be identified for protection or restoration during the design and construction process.

Through the design process, techniques should be used to minimize negative impacts on soil, water, and vegetation on the site and on adjacent sites that are to be preserved or restored. Develop details and specifications that support the use of native plantings, maintain existing biodiversity, and promote enhancement of site conditions per the B3 Guidelines.

A preconstruction meeting should be held to identify requirements for protection/preservation of vegetation during and after the construction process. Submittals should be monitored for compliance with plans and details. Bidders should be made aware of specific responsibilities for integrating the onsite vegetation management with connections to vegetation on adjacent sites. Existing plants and trees that will remain should be protected, and soil and water conditions maintained or improved to promote and improve vegetation growth.

An O&M manual should be created to protect and maintain onsite vegetation. The existing conditions of the vegetation should be documented, as should the reason the vegetation was preserved or enhanced, and its ability to function in its current capacity. The necessary enhancements needed to accommodate a different building type in the future should be noted, as well as what the enlargements or reductions in spatial area would be.

Pollinator friendly plantings should be selected from the lists below for compliance with S.4H:

To calculate the site albedo: On the project site plan, measure all areas in square footage that are exposed to sun during noon on June 22nd and determine the albedo value of the area according to its color. For living plants, use expected growth in ten years after the project is completed for square footage.

Calculate the total proposed site albedo using Appendix S-4: Site Albedo Calculator. The total site albedo as determined by this calculation must be at least 0.25 (25%) (or 0.30 (30%) if pursuing S.4I). Submit a site plan with each site material and albedo values identified and the completed Appendix S-4.

Using https://www.pca.state.mn.us/water/floristic-quality-assessment and the available FQA calculator and instructions, ensure that the site achieves at least a score of 4.0.

Predesign

  • 4A: Identification of any critical site conditions.
  • 4J: Plant design matrix for genera, species, and structural diversity of planting that meet S.4K (and other
  • relevant guidelines).

Design:

  • 4B: Verification of intended compliance and preliminary calculations of tree trunk areas, tree soil volumes, tree soil diversity and preliminary specifications outlining tree planting methods.
  • 4C: Verification of intended compliance and preliminary calculations for all required vegetation conditions, including planting plan for each plant category identified in the Predesign matrix for genera, species, and structural diversity of planting guidelines, updated as needed.
  • 4D: Verification of preliminary selection of pollinator friendly plantings.
  • 4E: Identification of major ecosystem and preliminary intended method of compliance of biomass target.
  • 4J: (and S.4N if pursuing): Completed preliminary Appendix S-4 Albedo Calculator demonstrating anticipated design compliance with albedo limits.

Final Design:

  • 4B: Verification of language mandating compliance in construction documents for tree trunk areas, tree soil volumes, tree soil diversity and specifications outlining tree planting methods.
  • 4C: Verification of compliance method in construction documents for all required vegetation conditions, including planting plan for each plant category identified in the Predesign matrix for genera, species, and structural diversity of planting guidelines, updated from prior iterations.
  • 4D: Verification of selection of pollinator friendly plantings and specifications prohibiting using neonicotinoid products during the establishment, maintenance, and operation of the site.
  • 4E Identification of major ecosystem and construction documents requiring compliance with biomass target.
  • 4F (and S.4I if pursuing): Completed Appendix S-4 Albedo Calculator demonstrating compliance with albedo limits. A site plan showing the location and size of areas with different reflective characteristics and their assigned albedo values should be included.
  • 4G: Planting plan demonstrating diversity of native plant species.
  • 4H: Documentation of NPCs, including site plan and documentation of correspondence and implementation of recommendations of DNR Heritage Division staff.

Closeout:

  • 4B: Verification of language mandating compliance in construction documents and guidelines requirement compliance if trees are surrounded by hard surfaces. Final planting plan for each plant category identified in the final design matrix for genera, species, and structural diversity of planting that meet required genera diversity, updated as needed and verifying that substitutes were not implemented for more than 5% of trees, shrubs, vines, or perennials.

‘Understanding Site and Water in B3 Version 3.1’ Training Session Video (YouTube)

‘Understanding Site and Water in B3 Version 3.1’ Training Session Slides (PDF)

Appendix S-4 Site Albedo Calculator

Coffin, Barbara and Pfannmuller, Lee. 1988. Minnesota’s Endangered Flora and Fauna. Minnesota: University of Minnesota Press.

Dirr, Michael. 1990. Manual of Woody Plants. Illinois: Stipes Pub.

Hightshoe, Gary. 1988. Native Trees, Shrubs, and Vines for Urban and Rural America: A Planting Design Manual for Environmental Designer. New York: Van Nostrand Reinhold.

International Society of Arboriculture: www.isa-arbor.com/publications/tree-ord/ordprt3d.aspx.

MacDonagh, L. Peter, 2005. Minnesota Soil Bioengineering Handbook. Minnesota: MnDOT.

Minnesota Board of Water and Soil Resources: https://bwsr.state.mn.us/.

Minnesota Department of Agriculture, Invasive Species: https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21429.

MN DNR, Invasive Species: http://dnr.state.mn.us/invasives/terrestrialplants/index.html.

MnDOT, Native Seed Mix Design for Roadsides, May 2010. www.dot.state.mn.us/environment/erosion/pdf/native-seed-mix-dm.pdf.

Smith, Welby. 2008. Trees and Shrubs of Minnesota: The Complete Guide to Species Identification. Minnesota: University of Minnesota Press.

Swink, Floyd and Wilhelm, Gerould. 1994. Plants of the Chicago Region. Indiana Academy of Science.

Sutton, Richard K., ed. 2015. Green Roof Ecosystem. Springer International Publishing. (See Chapter 11.)

Urban, James. Up By The Roots, International Society for Arboriculture 2008: http://www.jamesurban.net/up-by-roots/.

University of Florida Landscape Plants guidance by Ed Gillman http://hort.ifas.ufl.edu/woody/.

USDA Electronic Field Office Technical Guide (eFOTG): https://www.nrcs.usda.gov/resources/guides-and-instructions/field-office-technical-guides.

Wild Ones Pollinator Garden Campaign: www.wildones.org.

Seeding Manual – Latest Edition, Mn/DOT Office of Environmental Services, Turf Establishment & Erosion Control Unit https://www.dot.state.mn.us/environment/erosion/vegetation.html

The Minnesota County Biological Survey: https://www.dnr.state.mn.us/eco/mbs/index.html

United States Dept. of Agriculture, Natural Resources Conservation Service, Engineering Field Handbook: https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21429

Xerces Society Pollinator Conservation: http://xerces.org/pollinator-conservation/

DNR Pollinator Best Management Practices and Habitat Restoration Guidelines: http://files.dnr.state.mn.us/natural_resources/npc/2014_draft_pollinator_bmp_guidelines.pdf

University of Minnesota Bee Lab “Plants for Minnesota Bees”: https://beelab.umn.edu/help-bees/actions-help-bees/plant-bee-flowers

Minnesota Department of Agriculture, Noxious Weed List: https://www.mda.state.mn.us/plants-insects/minnesota-noxious-weed-list

Minnesota Department of Agriculture Conservation Funding Guide: http://www2.mda.state.mn.us/webapp/cpdt/queryBuilder_new.jsp

International Society of Arboriculture: www.isa-arbor.com/publications/tree-ord/ordprt3d.aspx

Board of Water and Soil Resources: https://bwsr.state.mn.us/

Albedo:

Exterior surface reflectivity index, or the capacity of a surface to reflect back light as evaluated across a specified range of frequencies.

Biomass:

The standing dry weight of all vegetation, typically measured in kilograms per square meter.

Coefficient of Conservancy/Floristic Quality Assessment (FQA):

An ecological integrity evaluation tool for NPCs, pioneered by Wilhelm (1977) and later refined by Swink and Wilhelm (1979, 1994). Currently, all 50 states use FQA systems. All plants within a subject community are scored from 0–10, from most to least invasive (e.g., in Minnesota: common buckthorn Rhamnus cathartica = 0; pink and white ladyslipper orchid Cypripedium reginae = 10).

Cultivar or CV:

Named variety of a hybrid plant species e.g., Iris “Caeser’s Brother” is an Iris siberica crossed Iris sanguinea hybrid. CVs are generally more vulnerable to pest infestations and usually lack pollen or nectar in their flowers.

Ecosystem Provinces:

Major ecosystem zones with distinctive physical structures and groupings of plants (trees, shrubs, vines, herbaceous) with unique soil orders, precipitation, climate, and specific stochastic disturbance regimes, such as winds, fire, or floods.

Historical Context or European Presettlement:

Refers to native landcovers in Minnesota prior to 1840.

Tree Sizes:

Large, medium, and small refer to the ultimate mature dimensions of that tree species, not tree size at time of planting. For example, hybrid elm, burr oak, hackberry, American linden, white pine, etc. would be considered large trees.

Tree Species:

Primary taxonomic classification, ranking below genus.

Tree Genera:

Second-level of scientific species classification, (e.g., maples: Acer, oak: Quercus, elms: Ulmus are all tree genera). Note that as multiple species (cultivars) may be of the same genera; if multiple species or cultivars are selected for a site which belong to a single genera, only a single genera is represented by those selections.

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