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Chapter 4
Construction Practices for Environmental Stewardship
4.10. Vegetation Management in Construction

Construction practices have a potentially greater influence on a DOT's ongoing maintenance situation regarding vegetation management, than any other part of the organization.

 

4.10.1 General Weed Prevention Practices for Site-Disturbing Projects in Construction

In general

  • A noxious weed abatement program should be implemented:
    • Construction equipment should be steam-cleaned and inspected to ensure that it arrives on site free of mud and seed-bearing material.
    • Seeds and straw material should be certified as weed-free.
    • Areas of noxious weeds should be identified and treated prior to construction.
  • In situations where mechanical controls are not enough, the application of fertilizers and the use of herbicides to suppress undesirable competing species may be necessary. Herbicides can eliminate undesirable species more reliably, but they may eliminate desirable species. Their use near watercourses may also be severely curtailed by local, state, and federal permit requirements. Several herbicides are approved for near-stream use and degrade quickly, but their use should be considered a last resort and the effects of excessive spray or overspray carefully controlled. If herbicide use is both advisable and permitted, the specific choice should be based first on whether the herbicide is absorbed by the leaves or by the roots (e.g., Jacoby 1987). [N] The most common foliar-absorbed herbicide is 2,4-D, manufactured by numerous companies and particularly effective on broadleaf weeds and some shrubs. Other foliar herbicides have become available more recently and are commonly mixed with 2,4-D for broad-spectrum control. Root-absorbed herbicides are either sprayed (commonly mixed with dye to show the area of application) or spread in granular form. They persist longer than most foliar herbicides, and some are formulated to kill newly sprouted weeds for some time after application.
  • Areas treated to remove noxious weeds should be revegetated with appropriate native species.

The following weed prevention practices for construction projects and maintenance programs are synthesized from practices recommended by NYSDOT [N] and the U.S. Forest Service [N], two of the more complete sets of practices offered by managers of linear corridors in the U.S.

  1. Provide tools for inspection/enforcement/results by incorporating, as appropriate, standard specifications, special specifications, notes and special notes as described in the previous section.
  2. Identification, awareness, and education - Once you know which invasive species are a priority in your area, learn to identify these plants. Improve effectiveness of prevention practices through weed awareness and education.
    • Provide information, training and appropriate weed identification materials to people potentially involved in weed introduction, establishment, and spread on agency lands, including agency managers, employees, contract workers, permit holders, and recreational visitors. Educate them to an appropriate level in weed identification, biology, impacts, and effective prevention measures.
    • Provide proficient weed management expertise at each administrative unit. Expertise means that necessary skills are available and corporate knowledge is maintained.
    • Develop incentive programs encouraging weed awareness detection, reporting, and for locating new invaders.
    • During Project Construction Phase, ensure that provisions for location, prevention and control of invasive species are understood by Department Construction staff and Contractor staff prior to construction and implemented throughout the project. Invasive species considerations should be routinely addressed by Department staff to Contractor staff during pre-bid, pre-construction, get-start and weekly safety meetings, as appropriate.
  1. Inventory - Developing an inventory of the priority invasive plants on your site or in your management area is important for several reasons. First and foremost, knowing where the invasive plants live is essential to control efforts; by definition, the species will continue to exist and spread until they are controlled. Finally, since new invaders can show-up at any time and are easiest to control when they first arise in an area, regular checking of the site(s) and updating of the inventory is important.
    • Before ground-disturbing activities begin, inventory and prioritize weed infestations for treatment in project operating areas and along access routes.
    • Identify what weeds are on site, or within reasonably expected potential invasion vicinity, and do a risk assessment accordingly.
    • Any additional priority invasive species populations encountered within the project area during construction should be noted and if invasive species within the project limits are not adequately controlled, the Regional Maintenance Engineer should be notified immediately so that controls can be addressed post construction.
    • To assist with future control efforts, during the Operation and Maintenance of all elements of the state transportation system, the agency shall initiate a system and Regions are encouraged to formally identify and inventory priority invasive species known to exist along the roadside within and immediately adjacent to the ROW. Due to their heightened role in the introduction and spread of invasive species, priority areas to initiate invasive species inventory efforts shall be the interstate, expressway and parkway systems, as practical. Additional priority species and inventory locations may develop as the result of Region-wide planning efforts and should also be considered. This inventory should also provide information regarding the extent of invasive species populations adjacent to and outside the ROW. Identified priority invasive species will be considered and managed as appropriate to: (1) limit additional introduction of invasive species; (2) limit the further spread of invasive species; and (3) eradicate or control existing invasive species populations.
  1. Incorporate weed prevention and control into project layout, design, alternative evaluation, and project decisions.
    • For the site or maintenance program in question, assess weed risks, analyze potential treatment of high-risk sites for weed establishment and spread, and identify prevention practices.
    • Determine prevention and maintenance needs, to include the use of herbicides, if needed, at the onset of project planning.
  1. Control weeds as necessary.
    • Begin project operations in uninfested areas before operating in weed-infested areas.
    • Locate and use weed-free project staging areas.
    • Avoid or minimize all types of travel through weed- infested areas, or restrict to those periods when spread of seed or propagules are least likely.
    • Coordinate project activities with any nearby herbicide application to maximize cost effectiveness of weed treatments.
    • Evaluate options, including closure, to regulate the flow of traffic on sites where desired vegetation needs to be established. Sites could include road and trail rights-of-way, and other areas of disturbed soils.
  1. Minimize Soil Disturbance - Due to the nature of invasive plants to rapidly colonize areas of disturbed soil, out-compete native species and become firmly established very quickly, it is essential to minimize areas of soil disturbance.
    • In those vegetation types with relatively closed canopies, retain shade to the extent possible to suppress weeds and prevent their establishment and growth.
    • Avoid creating soil conditions that promote weed germination and establishment.
    • Minimize soil disturbance to the extent practical, consistent with project objectives.
  1. Materials Sources - Prevent the introduction and spread of weeds caused by moving infested sand, gravel, borrow, and fill material by inspect material sources on site, and ensure that they are weed- free before use and transport. Treat weed-infested sources for eradication, and strip and stockpile contaminated material before any use of pit material.
    • Inspect and document the area where material from treated weed- infested sources is used, annually for at least three years after project completion, to ensure that any weeds transported to the site are promptly detected and controlled.
    • Maintain stockpiled, uninfested material in a weed-free condition.
    • Avoid or remove sources of weed seed and propagules to prevent new weed infestations and the spread of existing weeds.
  1. Temporary Erosion and Sediment Control - DOT policy requires sound temporary erosion and sediment control practices on all projects that disturb soil. This practice is particularly important in preventing the introduction and continued spread of invasive plant species. Where invasive species are known to exist, rapid and diligent erosion and sediment control, is particularly important.
  2. Mulch - Due to the nature of invasive plants to rapidly colonize any area of disturbed soil, it is essential that all disturbed areas be mulched and seeded as soon as possible. If outside the growing season for seed germination, disturbed sites should still be mulched. Sources of mulch should be free of invasive plant parts or seeds. Use of straw or wood fiber mulch is preferred. If hay mulch is used, it should be verified as originating from an invasive free source.
  3. Early Detection and Rapid Response - Invasive species, by their nature, spread very rapidly once introduced to a new area. Therefore it is essential that new infestations be identified and controlled as quickly as possible. Control practices for small populations are far more likely to succeed, are significantly less expensive, and provide more options for control methodology.
  4. Rapid Revegetation - Although not a specific condition, replanting or reseeding with native species is highly desired. All of the control methods below are aimed at reducing or eliminating invasive species so that natives are encouraged to grow and re-establish stable conditions that are not conducive to invasive colonization. In most cases removal or reduction of invasive populations will be enough to release native species and re-establish their dominance on a site. Replanting may be desirable on private lands where it can be used as a quid pro quo with the landowner for permission to remove invasive plants. Where project disturbance creates bare ground, consistent with project objectives, reestablish vegetation to prevent conditions to establish weeds.
    • Revegetate disturbed soil (except travelways on surfaced projects) in a manner that optimizes plant establishment for that specific site. Define for each project what constitutes disturbed soil and objectives for plant cover revegetation.
    • Revegetation may include topsoil replacement, planting, seeding, fertilization, liming, and weed-free mulching as necessary. Use native material where appropriate and feasible. Use certified weed-free or weed-seed-free hay or straw where certified materials are required and/or are reasonably available. Always use certified materials in areas closed by administrative order. Where practical, stockpile weed-seed-free topsoil and replace it on disturbed areas (e.g. road embankments or landings).
    • Use local seeding guidelines to determine detailed procedures and appropriate mixes. To avoid weed-contamination, a certified seed laboratory needs to test each lot against the all-State noxious weed list to Association of Seed Technologists and Analysts (AOSTA) standards, and provide documentation of the seed inspection test. There are plant species not on State and Federal noxious weed lists that the Forest Service would consider non-native invasive weeds. Check State and Federal lists to see if any local weeds need to be added prior to testing. Seed lots labeled as certified weed free at time of sale may still contain some weed seed contamination. Non-certified seed should first be tested before use.
    • Inspect and document all limited term ground-disturbing operations in noxious weed infested areas for at least three (3) growing seasons following completion of the project. For on-going projects, continue to monitor until reasonable certainty is obtained that no weeds have occurred. Provide for follow-up treatments based on inspection results.
  1. Ditching - Many priority invasive plants prefer moist soil conditions and are tolerant of saline environments; therefore they grow very well in highway drainage ditches and other components of the drainage system. As the dense root systems of invasive plants such as purple loosestrife, phragmites and Japanese knotweed proliferate, they rapidly clog drainage ditches and reduce sight distances, especially where water velocities slow, e.g. up gradient of culvert inverts, above check dams, etc. Due to the rapid growth of invasive plants, maintenance cycles are far more frequent where they exist. Prior to excavating the plants from drainage ditches, the entire invasive plant infestation should be treated with the appropriate herbicide, e.g. Rodeo or other aquatic-use registered herbicide. This will ensure that the plants, seeds and root parts will not spread and re-establish. Failure to treat the invasive plants prior to physical removal will most likely result in immediate re-growth of the plants in the ditch and the spread of the plant to adjacent and downstream areas. In addition, if the invasive plants are not killed prior to ditch cleaning, the spoil produced can further spread the plants upon disposal;
  2. Shoulder Scraping - Removing the build-up of organic material along highway shoulders is essential to maintaining pavement quality, providing adequate sheet flow drainage and providing safe driving conditions. Due to their disturbed nature and harsh growing conditions, highway shoulders provide a prime area for invasive plants to establish and spread. Therefore shoulder scraping activities address invasive plant control, though scraping is not a desirable control method in and of itself. Prior to scraping highway shoulders, all existing priority invasive plants should be treated with appropriate herbicide or other control measure to kill seeds and plant parts, including the root stock. This will prevent the plant from reseeding, re-sprouting in-situ or spreading to adjacent areas via, water, wind, or hitching a ride on equipment or through spoil disposal.
  3. Vine, Brush and Tree Removal - Several common species of vines, brush and trees that grow profusely along highway roadsides are considered invasive species. These species frequently cause a nuisance to maintenance workers, block traffic signs or limit sight distances and therefore are removed in routine maintenance operations. In the evaluation of these removal priorities, invasive species should be given preference and controlled by accepted practices that will ensure no re-sprouting and prevent additional spread through seed dispersal. Since these species do not reproduce vegetatively, plant parts do not need to be buried or land-filled, and equipment does not require cleaning. Accepted methods of control include foliar herbicide treatment or cutting followed by stump treatment with herbicide. Mowing alone frequently results in re-sprouting and cloning and is not an effective control methodology;
  4. Poisonous Plant Removal - A few invasive species pose serious a threat to worker safety and public health. Giant Hogweed, Heraculeum mantegazzianum, is such a plant. Upon dermal contact this plant causes severe skin burns which are exacerbated through exposure to sunlight. Where this plant is encountered, the location should be located using GPS coordinates and reference markers identification, the size of the population should be noted and maintained in a regional database.
  5. Disposal - Proper disposal of harvested invasive plant parts and soil containing invasive plant seeds or root stock (rhizomes) is essential to controlling the spread of invasive plants. Full consideration should be given, as appropriate, as follows:
    • Transportation - While on the treatment site, bag all cut living plant material in heavy duty, 3 mil or thicker, black contractor quality plastic clean-up bags. Securely tie the bags and transport from the site in a truck with a topper or cap to securely fasten the load, in order to prevent spread of the plant material from the project work site. Transport the material to an appropriate disposal location.
    • Compost - Because of the extremely robust nature of invasive species, composting in a typical backyard compost pile or composting bin is not appropriate. However, methods can be used whereby sun-generated heat can be used to destroy the harvested plant materials. For instance, storage in a sealed 3 mil thickness (minimum) black plastic garbage bags on blacktop in the sun until the plant materials liquefy is effective. If a larger section of blacktop is available, make a black plastic (4 mil thickness minimum) envelope sealed on the edges with sand bags. The plant material left exposed to the sun will liquefy in the sealed envelope without danger of dispersal by wind. The bags or envelopes must be monitored to make sure the plants do not escape through rips, tears or seams in the plastic.
    • Bury - Due to the incredible capacity of many invasive species to reproduce by seed, clone and vegetative propagation, it is absolutely imperative that spoil material contaminated with invasive plant material NOT be disposed-of in an indiscriminant manner. It is recognized that the Contractor owns spoil material and therefore, contract documents should identify locations of contaminated soil and address disposal options. Spoil material that contains invasive plant material should be buried in an excavated pit, covered with woven geotextile and covered with at least three feet of uncontaminated fill material.
    • Landfill - If harvested invasive plant parts or spoil material containing invasive plant material is not composted or buried, it should be transported directly to a sanitary landfill for proper disposal.
  1. Bridge Washing - All bridge washing activities, whether for biannual maintenance or in preparation for re-painting, require the use of water. Several invasive plant and animal species are aquatic or are dispersed through water, therefore, DOT activities that require the transport and use of water need to consider invasive species control. Control considerations include use of municipal water sources, filters on water intakes, decontamination/sanitation of equipment and use of in-situ water sources. In addition, the equipment used in transporting and spraying water should be cleaned prior to use or between use at sites in different watersheds.
  2. Construction Equipment in Water Bodies - Several invasive species are aquatic and many additional non-aquatic species are readily spread by the movement of flowing water. Many aquatic invasive species are capable of survival out of water for extended periods. To prevent the accidental introduction of invasive species that are "hitching a ride" on construction equipment, all equipment that is to be placed in a water body should be cleaned, as appropriate, e.g. tracks, buckets, to remove invasive species and their seeds and propagules. This requirement applies to equipment arriving on the project and equipment that is being relocated within the project;
  3. Restricted Construction Equipment Access - To prevent the accidental introduction of invasive plants during construction or maintenance activities, all tracked equipment involved in earthwork should be cleaned to remove plants, seeds and propagules that may be hitchhiking, prior to arrival on-site. If tracked equipment is used in earth work on a portion of a project where invasive species are known to exist, this portion of the earthwork should be conducted last, or the equipment shall be cleaned prior to use on any portion of the site that is known to be free of invasive plants; and
  4. Cleaning of Construction Equipment - Cleaning should occur prior to equipment arriving on-site. Once on-site, if equipment involved in earthwork is contaminated with invasive species, the equipment should be cleaned prior to moving into uncontaminated areas. Cleaning shall consist of using physical means and hand tools, such as brushes, brooms, rakes or shovels, on all track and bucket/blade components to adequately remove all visible dirt and plant debris. If water is used, the water/slurry shall be contained so as to restrict introduction of invasive plants, seeds and propagules into the project or off-site through future surplus material disposal.
    • Treat weeds at administrative sites and use weed prevention practices to maintain sites in a weed-free condition.
    • Determine the need for, and when appropriate, identify sites where equipment can be cleaned. Clean equipment before entering area targeted for prevention of invasive, including federal forest and park lands. When practical, collect and incinerate plant parts. Remove mud, dirt, and plant parts from project equipment before moving it into a project area.
    • Clean all equipment, before leaving the project site, if operating in areas infested with weeds. Determine the need for, and when appropriate, identify sites where equipment can be cleaned. Seeds and plant parts need to be collected when practical and incinerated.
    • Workers need to inspect, remove, and properly dispose of weed seed and plant parts found on their clothing and equipment. Proper disposal means bagging the seeds and plant parts and incinerating them.
  1. Set the example; maintain weed- free administrative sites.

 

4.10.2 Potential Construction Contract Wording and Measures for Invasive Species Control
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The Center for Invasive Plants Management recommends the following contract language for weed prevention: [N]

  • Prior to any construction disturbance you will:
    • Identify and map all noxious and invasive weed populations present in the project area.
    • Treat or contain any weed populations that may be impacted or disturbed by construction activity.
    • Flag all weed populations to be avoided.
    • Provide training to construction workers and equipment operators on the identification of weeds to be avoided.
    • Certify that all construction material sources used for supplies of sand, gravel, rock and mulch are weed-free prior to obtaining or transporting any material from them.Obtain and use only certified weed-free straw or use fiber roll logs for sediment containment.
    • Wash and inspect all vehicles for weed seeds and plant parts prior to bringing them onto the job site.
    • Install stormwater Best Management Practices to prevent erosion of the job site and the potential transport of weedy material onto or off of the job site.
  • During construction you will:
    • Minimize ground disturbance and vegetation removal as much as possible and practical.
    • Wash, or using an air compressor, blow clean all vehicles (including tires and undercarriage) that may have entered weed-infested areas prior to entering uninfested areas of the job site.
    • Restrict vehicles or other traffic that may transport weed seeds or plant material from entering the job site unless they are first washed and inspected.
  • After construction is complete you will:
    • Revegetate or otherwise prevent the establishment of weeds in all areas of the job site through a program of monitoring and post-construction weed treatment for the life of the project.
    • Revegetate using soil components and mulches obtained from non-weed infested sources.
    • Utilize seed and other plant material that has been checked and certified as noxious weed-free and that has a weed content of 0.05 percent or less.
    • Revegetate using plant materials that have a high likelihood of survival.
    • Maintain all planted material and native vegetation located on the project site for the life of the project.
    • Monitor all seeded sites for weed infestation. Treat all weeds adjacent to newly seeded areas prior to planting and treat planted areas for weeds in the first growing season.
  • NYSDOT utilizes the following contract item methods of measurement:
    • Controlling invasive plants will be measured as the number of square meters of surface area that have been satisfactorily controlled. The unit price bid per square meter shall include the cost of all labor, materials and equipment, including disposal, and incidentals necessary to complete the work.

      Item Pay Unit
      Controlling Invasive Plants with Plastic Square Meter
      Controlling Invasive Plants with Herbicides Square Meter
      Controlling Invasive Plants by Pulling Square Meter
      Controlling Invasive Plants by Digging Square Meter

 

4.10.3 Review and Pretreatment of Construction and Materials Sites
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Pre-construction planning and treatment to reduce infestations of invasives is on the upswing. [N] Nine DOTs (23% of respondents) said that all construction sites are reviewed for invasive species before opening. [N] Wyoming DOT is among five that are working at pretreating construction zones prior to soil disturbance.

WYDOT is trying to develop a more aggressive pit assessment and treatment program with local Weed & Pest districts. These sources have been identified as having the greatest potential for spreading invasives. At Nevada DOT a staff biologist surveys material source sites for invasives. When invasives are found, a management plan is developed in cooperation with the local BLM weed coordinator or botanist. Environmental Services is developing standard noxious weed control BMP specifications for weed management on material sites and project sites. Eight other DOTs (23% of respondents) also ensure dirt and gravel sources are evaluated.

In addition:

  • Over a third of DOTs (17 total) specify weed-free mulches on all projects. Inert mulch products such as straw or wood fiber are used in sensitive areas by 11 DOTs (28% of respondents).
  • Twenty-one state DOTs (53% of respondents) specify on project plans and bid contracts that seed and sod sources must be free of invasive species and/or weeds.

Possible solutions to the problem of weeds that are introduced by animal feed or mulches contaminated with weed seed are discussed in Certified Weed Free Forage: An Emerging Program for Western States, by UC-Davis.

 

4.10.4 Protection of Native Populations
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Intact communities of native species both suppress invasives and shelter rare species. Thirty-eight percent (38%) of responding DOTs (15 states) are now screening for the presence of rare plant communities in the work zone or ROW. [N] In 13 states, areas in need of special management are identified by resource agencies or state Natural Heritage Program. [N] North Carolina DOT, like many others, works cooperatively with their state Department of Environment and Natural Resources, in-house Botanists, and others to identify and protect state and federally endangered plant and animal species found on our rights-of-way. Oregon DOT has special management areas marked with signs that indicated the types and timing of maintenance techniques that are to be performed. Since Wisconsin DOT (WisDOT) hires County Highway Departments to perform highway maintenance, WisDOT has let several contracts to manage/restore high quality remnant plant communities discovered on the rights-of-way. Management plans are often developed to inventory and ensure appropriate management of special areas. Ten DOTs (25% of respondents) have taken it upon themselves to map and track protected communities on the DOT ROW, statewide.

Staff at 14 DOTs (35% of respondents) identify special management areas, which are managed accordingly by maintenance forces. [N] As Illinois DOT described, commitments are added to plans and DOT staff are trained on how to maintain these areas through mowing, herbicide applications and burning. Protected species are identified and restricted maintenance practices are incorporated to protect the endangered species; construction practices are also altered to minimize disturbances of native plant communities whenever possible (NV). In several states, from Wisconsin to New York, special vegetation management programs have been developed to protect Karner Blue Butterfly habitat, including mowing date restrictions and native blue lupine and butterfly weed restoration planting and seeding. The Louisiana Department of Transportation Development (LADOTD) has taken high value remnant strips in several districts and moved them just beyond the ROW, with the consent of the owners of that property and discussions regarding proper management. If moving them is not deemed an option, LADOTD marks the site to prevent herbicide applications or mowing at the wrong time of year.

In most cases, DOTs are taking these conservation measures without knowing the total acreage of high quality forest, wetland, or native grassland remnants they have or are protecting in the ROW. Just 15 percent of those responding (6 states) could provide such an estimate, if asked. More than a third of DOTs (43% of respondents - 17 states) identify native/rare plant communities in EAs and EISs. [N] In fact, Hawaii DOT indicated that most of their protected areas have been identified as a result of EAs, EISs, and Special Management Areas.

 

4.10.5 Vehicle Cleaning Practices
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Vehicle and equipment cleaning procedures and practices are typically used to minimize or eliminate the discharge of pollutants from vehicle and equipment cleaning operations to storm drain systems or watercourses, and to minimize transport of invasive species. Twenty-three percent of responding DOTs (9 DOTs) say they ensure vehicles are washed before and after use, to control the spread of invasive species. Caltrans is among the DOTs that have developed an extensive set of construction vehicle cleaning environmental stewardship practices. [N]

 

4.10.6 Revegetation
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Some DOTs are undertaking research to identify what vegetation establishment methods work best in their states and ecoregions. Studies on compost usage are occurring in the west and mid-west, from Texas in the south to Idaho in the north. The Nebraska Department of Roads has research results due soon, which will be used to develop technical guidelines for vegetation establishment on roadway shoulders. The project is examining the interaction effects of seed priming, type of mulch, and level of irrigation on soil movement and establishment of the short grass mixture on the foreslope of roadway shoulders; and the interaction effects of composted manure applications and a six to twelve inch compacted buffer strip between the paved shoulder and the seedbed on soil movement and establishment of the short grass mixture on the foreslope of the roadway. Delaware DOT is also publishing a vegetation management manual, in conjunction with the agency's tree preservation policy for a Livable Delaware. [N]

 

4.10.7 Shoulder Grading
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DOTs are teaching maintenance staff that shoulder grading is not acceptable as a method of vegetation or invasive species control. Shoulder grading is only promoted as a means of refining lateral support for the road.

 

4.10.8 Revegetation and Vegetation Salvage Plan
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A number of states have developed revegetation and vegetation salvage plans.Arizona DOT has a policy for salvage and replanting native trees and shrubs and plants, with up to $200,000 per mile for major species. [N] Revegetation and salvage may occur more easily in more humid environments with faster re-growth. Recommended practices for revegetation and vegetation salvage include the following.

  • A revegetation plan should be developed to ensure that salvage vegetation is used where possible and that native species are used. Monitoring will occur during the revegetation period to ensure the success of the revegetation plan.
  • Include at least a one-year plant establishment guarantee period from the contractor.
  • Follow guidelines or specifications for protection/restoration of existing vegetation. To protect existing desirable vegetation from construction impacts: [N]
  • Identify and delineate in contract documents all vegetation to be retained and mark in the field prior to the start of adjacent soil-disturbing activities. Mark areas to be preserved with orange polypropylene temporary fencing.
  • Minimize disturbed areas by locating temporary roadways to avoid stands of trees and shrubs and to follow existing contours to reduce cutting and filling.
  • When removing vegetation, consider impacts (increased exposure or wind damage) to the adjacent vegetation that will be preserved.
  • Protect the root zone of vegetation out to 1.5 times the diameter of the drip line, which is the outermost reach of its branches (the drip line).
  • If cuts or fills are required in the vicinity of trees to be saved, consider retaining walls, tree wells, gravel, or drainage systems to protect the root systems.
  • Avoid storing, parking or driving heavy equipment around the base of a tree, which can compact the soil and deprive the tree's roots of the water and air they need to survive. Stockpiling building materials or fill can have a similar effect. Refer to the Soils and Soil Amendments section for more information on soil compaction and its minimization.
  • Avoid scraping soil from roots or cutting them too deeply or too close to the tree can cause the tree to die or have a weakened hold and blow down. This damage may not be visible for years .

Mn/DOT has developed a Specification for Protection and Restoration of Vegetation. This specification promotes the protection and preservation of vegetation from damage and the use of corrective action when damage does occur. [N]

Example 11 : Mn/DOT Specification for Protection and Restoration of Vegetation Construction Elements

A. Protecting and Preserving

The Contractor shall protect and preserve:

Specimen trees.

  1. Threatened and endangered plants, as listed on the federal and state threatened and endangered species list.
  2. Vegetation designated in the Contract to be preserved.
  3. Trees, brush, and natural scenic elements within the right-of-way and outside the actual limits of clearing and grubbing.
  4. Other vegetation the Engineer identifies for protection and preservation.

The Contractor shall not place temporary structures, store material, or conduct unnecessary construction activities within a distance of 25 feet outside of the dripline of trees designated to be preserved without approval from the Engineer. The Contractor shall not place temporary structures or store material (including common borrow and topsoil ) outside of the construction limits in areas designated in the Contract to be preserved.

A1 Temporary Fence

The Contractor shall place temporary fences to protect vegetation before starting construction.

The Contractor shall place temporary fence at the construction limits and at other locations adjacent to vegetation designated to be preserved when specified in the Contract, directed by the Engineer, or allowed by the Engineer. The Contractor shall not remove the fence until all work is completed or until removal is allowed by the Engineer. The fence shall prevent traffic movement and the placement of temporary facilities, equipment, stockpiles, and supplies from harming the vegetation.

A2 Clean Root Cutting

The Contractor shall cleanly cut all tree roots at the construction limits when specified in the Contract or directed by the Engineer.

The Contractor shall immediately and cleanly cut damaged and exposed roots of trees designated for protection back to sound healthy tissue and shall immediately place topsoil over the exposed roots. The Contractor shall limit cutting to a minimum depth necessary for construction and shall use a vibratory plow or other approved root cutter prior to excavation. The Contractor shall immediately cover root ends that are exposed by excavation activities to within 6 inches of topsoil as measured outward from root ends.

A8 Destroyed or Disfigured Vegetation

If the Contractor destroys or disfigures vegetation designated to be preserved, the Contractor shall, at no expense to the Department, restore the damaged vegetation to a condition equal to what existed before the damage was done. The Engineer may assess damages against the Contractor on vegetation where an equal level of restoration is not accomplished. The Engineer will assess damages to trees and landscaping at not less than the appraisal damages as determined by the International Society of Arboriculture appraisal guide. The Engineer will determine and assess damages to other vegetation.

A10 Other Vegetation Protection Measures

The Contractor shall provide other vegetation protection measures, including root system bridging, compaction reduction, aeration, and retaining walls, as specified in the Contract or as directed by the Engineer.

Table 7.1

4.10.9 Site Preparation
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An adequately prepared site will have these characteristics: [N]

  • Free of construction debris.
  • Relatively few large rocks or other natural objects.
  • Free of ruts or gullies.
  • Top two inches should be in a friable condition (non-compacted), ideally allowing a heel to make a ¼-inch impression.
  • Heavily compacted sites should be scarified to a depth of 6 to 8 inches.

Availability of soil preparation equipment is often limited, but the Contractor can often use standard construction machinery. For example, ripper teeth on a grader tool bar will adequately prepare a site. Ideally, scarification will be done in two passes perpendicular to each other. However, on sloping land and in areas of high wind, use mono-directional scarification perpendicular to the direction of slope or prevailing wind. If traditional surface preparation equipment such as disks and/or chisel plows are available, the conditions required for adequate surface preparation are the same as previously noted.

 

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Table of Contents
 
Chapter 4
Construction Practices for Environmental Stewardship
4.1 General Construction Site Stewardship Practices
4.2 Work Area
4.3 Construction Involving Historic Properties and/or Other Cultural Resources
4.4 Construction in and around Drainage Areas and Streams, Wetlands, and Other Environmentally Sensitive Areas
4.5 Erosion and Sedimentation Control
4.6 Vehicle Fluid, Fuel, and Washwater Control
4.7 Air Quality Control Practices
4.8 Noise Minimization
4.9 Materials Storage, Collection and Spill Prevention on Construction Sites
4.10 Vegetation Management in Construction
4.11 Soil Management in Construction
4.12 Establishing Vegetation at Construction Sites
   
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