Protecting trees on sites under development or redevelopment is a complex process and requires skills, knowledge, and enforceable standards to be successful. Here are some important items to consider.

A sound jurisdictional foundation for tree protection is comprised of:

  • Local ordinances that specify the circumstances under which tree protection will be required, what constitutes an appropriate tree protection plan, how the tree protection plan will be evaluated for approval, how it will be enforced, and enforcement measures for violations.
  • Qualified staff to assess the viability of tree protection plans based on tree- and site-specific factors.
  • Established tree protection plan criteria, such as standard notes and details, and other specifications for tree protection that are written or otherwise endorsed by the jurisdiction.
  • Field staff trained to inspect and enforce the use, installation, and maintenance of approved tree protection measures.
  • Political, administrative, and community support for tree protection requirements.
Kirkland TP detail
City of Kirkland standard notes and tree protection fencing detail for inclusion in tree protection plans. Image provided by Deb Powers, City Forester, Planning Department, City of Kirkland

Tree protection for a development site is, ideally, based on an analysis of intersecting factors such as:

  • The jurisdiction’s over-arching environmental and community goals as laid out in their Comprehensive Plan, small area plans, development guidelines, or other planning documents.
  • State, county, or local regulations, such as minimum tree density or canopy cover requirements, that apply to the parcel.
  • Size, shape, and dimensions of the land parcel slated for development.
  • Species, size, age, health, arrangement, and value of trees on the parcel; “value” may be monetary, ecological, or cultural.
  • Viability of the forest stand in the context of the development.
  • Existing conditions of the parcel such as presence or absence of site improvements, natural drainage patterns, soil types, topography, etc.
  • Proposed construction activities and the greater area of land disturbance needed to accomplish those activities.
  • Anticipated impact(s) to trees and hydrology as a result of development actions.
  • Effectiveness of proposed tree protection measures.

Types of construction-related damages that adversely affect trees are:

  • Mechanical injury. Trees may be physically damaged by vehicles, heavy equipment or hand tools. Bark, trunks, branches or roots may be scraped, fractured, crushed or broken.
  • Soil compaction. Vehicles, heavy equipment, dumpsters and stockpiled materials can crush or suffocate roots, reduce water infiltration into the soil, and kill beneficial soil microbes. The result is an overall decline in soil structure and function, unfavorable to tree root health and structural integrity.
  • Grade changes. Skinning topsoil from a construction site may tear off or damage the roots of nearby trees.  Raising the grade onsite may bury trees’ root flares and suffocate roots. Just a few inches of grade change may have significant impacts to the health and structural stability of trees.
  • Chemical exposure. Exhaust fumes, paint, gasoline, grease, oils and other chemical compounds are common on construction sites. Trees absorb these toxins, and may be adversely impacted if such chemicals are not contained, mitigated, or disposed of properly.
  • Improper pruning. Branches that may interfere with construction activities should be properly pruned by an ISA Certified Arborist prior to commencement of work, rather than being “truck-pruned” or hacked off by impatient construction workers.

    Vancouver Tree Protection fail
    These trees have been irreparably damaged due to one developer’s failure to comply with tree protection requirements. Soil compaction, grade change, and mechanical injury is evident. Photo provided by Charles Ray, Urban Forester, City of Vancouver, WA

Strategies to influence the success of tree protection plans may include:

  • Creating local ordinances governing tree protection and the development process that are explicit, flexible, and compliment other code requirements (rather than conflict with them).
  • Requiring that a tree protection plan be drafted and submitted in advance of, or at least in conjunction with all other development plan documents required of the applicant by the jurisdiction
  • Communicating elements and standards of approved tree protection plans to everyone involved in the project–property owner(s), general contractor, subcontractors, utility companies, city staff, neighbors, etc.
  • Installing and inspecting tree protection measures in the field prior to commencement of any other permitted development or construction activities.
  • Conducting regular follow-up inspections to ensure compliance with the approved plan and enforcing violations in a timely fashion as they arise.
  • Requiring that a copy of the tree protection plan to remain onsite at all times.
  • Rewarding developers and contractors that do a great job with tree protection through publicity or recognition.

The above recommendations are of course, easier said than done, however staff at DNR are available to assist city staff with implementation of tree protection policies in step-wise manner, appropriate to the needs of your community. Please feel free to contact us if you have questions, or consult the following resources for more information on the protection of tree during development:

Tree Protection on Construction and Development Sites, A Best Management Practices Guidebook for the Pacific Northwest, 2009

Trees and Development: A Technical Guide to Preservation of Trees During Land Development, 1998

Tree Preservation and Protection Ordinances in Washington State