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Department of Public Works

  • Tree Protection Guidelines

    Purpose

    Tree protection guidelines are established for projects subject to Chapter 8.52 ‘City Trees and Tree Protection’ and for projects for which compliance with the Tree Protection Guidelines is a condition of approval. Specifically, the guidelines seek to avoid negative impacts that may occur during construction such as:

    • Mechanical injury to roots, trunks or branches
    • Compaction of soil
    • Changes to existing grade which may expose or suffocate roots

    Definitions for standardized terms and diagrams are included in the guidelines.

    A. General Requirements

    1. Applicants may be asked to place a construction bond in the amount of the assessed value of the tree as determined using the most recent version of the International Society of Arboriculture guide to plant appraisal. In addition, fees for three years of maintenance may be required. The bond will be returned to the applicant upon successful completion of the project and upon verification that the trees have not sustained damage during construction. If damage has been sustained during construction, the City Manager or designee may hold the bond for an additional period of time.
    2. Violations to the Tree Protection Plan may result in fines assessed per day and imposed per violation, and the potential generation of a stop work order on the construction project.
    3. The tree protection plan may include written recommendations for the health and long-term welfare of the trees during the pre-construction, demolition, construction, and post-construction development phases. Notes on the plans would include specifics on avoiding injury, damage treatment and inspections of protected trees.

    B. Root Protection Zone

    1. Tree roots are generally located in the top 12–24 inches of soil and can extend to a distance exceeding the trees height and/or width. The roots located 3-5 feet from the trunk are often relatively inactive, and if cut, will cause a column of decay that can reach the top of the tree with time. The feeder roots of the tree can sustain damage during construction from lack of water, soil compaction or physical damage resulting from cutting. The following guidelines are designed to minimize damage to the root system of protected trees. These guidelines establish a “Root Protection Zone” to safeguard the health of protected trees.
    2. Protective chain-link fencing with an access gate of minimal width should be installed at the Root Protection Zone of protected trees and approved in place by staff prior to the commencement of any construction, or demolition.
    3. The protection zone should be irrigated sufficiently with clean potable water to keep the tree in good health and vigor before, during, and after construction. This may mean deeply soaking the ground periodically.
    4. No construction staging or disposal of construction materials or byproducts including but not limited to paint, plaster, or chemical solutions is allowed in the Root Protection Zone.
    5. The Root Protection Zone should not be subjected to flooding incidental to the construction work.
    6. All work conducted in the ground within the Root Protection Zone of any protected tree should be accomplished with hand tools, unless an air spade is utilized. Trenches in the Root Protection Zone should be tunneled, or completed with an air spade to avoid damage to small feeder roots within the root protection zone. Information regarding air spades is available from staff.
    7. Where structural footings are required and major roots (over 3” in diameter) will be impacted, the engineer of record should submit acceptable footing design alternatives and or location alternatives to staff before proceeding with further plan review.
    8. Where more than 50% of the root zone is impacted or roots greater than 3 inches in diameter are to be removed within four feet of the trunk, the engineer of record should submit acceptable design alternatives to staff for review.
    9. Any required trenching should be routed in such a manner as to minimize root damage. Radial trenching (radial to the tree trunk) is preferred as it is less harmful than tangential trenching. Construction activity should be diverted from the Root Protection Zone. Cutting of roots should be avoided (i.e. place pipes and cables below uncut roots). Wherever possible and in accordance with applicable code requirements, the same trench should be used for multiple utilities.
    10. “Natural” or pre-construction grade should be maintained in the Root Protection Zone. At no time during or after construction should soil be in contact with the trunk of the tree above the basal flair.
    11. In areas where the grade around the protected tree will be lowered, some root cutting may be unavoidable. Cuts should be clean and made at right angles to the roots. When practical, cut roots back to a branching lateral root.
    12. When removing existing pavement in the Root Protection Zone, avoid the use of heavy equipment, which will compact and damage the root system.
    13. If staff requires mulch in the Root Protection Zone the mulch materials and location should be shown on the plan. Larger projects will require construction staging plans to indicate where materials will be stored and how the equipment will move in and around the property to minimize damage to the Root Protection Zone and tree canopies. Root damage and soil compaction may be mitigated in some cases by using plywood or mulch in the Root Protection Zone.

    C. Pruning

    1. Pruning of all trees should be in accordance with industry standards ( International Society of Arboriculture or ANZI 133.1).
    2. Pruning of oaks should be limited to the removal of dead wood and the correction of potentially hazardous conditions, as evaluated by a qualified arborist. Excessive pruning is harmful to oaks. Removal or reduction of major structural limbs should be done only as required for actual building clearance or safety. If limbs must be removed, cuts should be made perpendicular to the branch, to limit the size of the cut face. The branch bark collar should be preserved (i. e. no “flush cuts”), and cuts should be made in such a way as to prevent the tearing of bark from the tree.
    3. Pruning of trees other than oaks should be limited to the removal or reduction of major structural limbs and should be done only as required for actual building clearance or safety. If limbs must be removed, cuts should be made perpendicular to the branch, to limit the size of the cut face. The branch bark collar should be preserved (i. e. no “flush cuts”), and cuts should be made in such a way as to prevent the tearing of bark from the tree.
    4. Landmark Trees must be pruned by or under the direction of a qualified arborist.

    D. Inspections

    1. Inspection of Protective Fencing: City staff may require inspection of fencing to verify placement and approval of materials prior to the commencement of construction.
    2. Pre-construction meeting. City staff may require an on-site pre-construction meeting with the contractor and or applicant to discuss tree protection with the site supervisor, grading equipment contractors, and demolition crew.
    3. Inspection of rough grading. City staff my require inspection to ensure protected trees will not be injured by compaction, cut or fill, drainage and trenching activities.
    4. Special Activity in the Tree Protection Zone: City staff may require the direct on-site supervision of work in the tree protection zone.
    5. Periodic Inspections: City staff may require inspections verifying adherence to tree protection measures during the on-going construction process. Allow a minimum of 48 hours for scheduling inspections.

    E. Definitions

    1. Basal flair or root crown means the tree trunk where it emerges from the root system and flairs out to create the base of the tree.
    2. Canopy means the area of a tree that consists primarily of branches and leaves.
    3. Dripline means the outermost area of the tree canopy (leafy area of tree).
    4. Certified Arborist means an individual who has demonstrated knowledge and competency through obtainment of the current International Society of Arboriculture arborist certification, or who is a member of the American Society of Consulting Arborists.
    5. Root Protection Zone means the area within a circle with a radius equal to the greatest distance from the trunk to any overhanging foliage in the tree canopy.