Tree Protection Policies

We’ve been receiving a lot of inquiries about tree protection policies. Here are two helpful resources to help guide you through the process:

1. Tree Protection Policy and Specifications for Construction Near Trees

2. Tree Preservation Guidelines (download or read below)

Establishment of Tree Protection Zone (TPZ)

• Tree preservation measures, including the establishment of Tree Protection Zone (TPZ) shall apply to the vegetation identified to be retained and protected. The Tree Protection Zone shall consist of tree protection fencing as per city of Markham standard t-1 and Region of York standard nhfs-04 and nhfs-04, placed at the dripline of vegetation to be preserved.
• No grade changes shall occur within Tree Protection Zone. In the advent that grade changes occur either as a cut or fill situation, the contract administrator must be notified so that precautions to preserve the tree can be determined prior to the placement of fill or excavation activities.
• Every precaution must be taken to prevent damage to trees and root systems from damage, compaction and contamination resulting from the construction to the satisfaction of the contract administrator.
• Trees that require pruning to permit construction activities will be done so in accordance with good arboricultural practices. In the event that it is necessary to remove additional limbs or portions of trees,after construction has commenced, to accommodate construction, the contract administrator is to be informed and under their direction the removal is to be executed carefully and in full accordance with arboricultural techniques by a certified arborist.
• Any damage to trees such as broken limbs, damage to roots, or wounds to the main trunk or stem systems are to be reported to the consulting arborist so that the damage can be assessed immediately and mitigation can be promptly implemented.

Root pruning practices

• During excavation operations in which the root area is affected, the contractor is to prune all exposed roots cleanly. Pruned root ends are to be neatly and squarely trimmed and the area is to be backfilled with clean native fill as soon as possible to prevent desiccation and promote root growth. The exposed roots should not be allowed to dry out, and the contractor shall discuss watering of the roots with the consulting arborist so that the roots shall maintain optimum soil moisture during construction and backfilling operations, yet so not to interfere with construction operations. Backfilling must be with clean uncontaminated topsoil from an approved source. Texture must be coarser than existing soils, and to come into clean contact with existing soils (remove air pockets, sod, etc.)
• Tree roots should not be excavated within the critical structural rooting area. This is the minimum area of the root system necessary to maintain vitality or stability of the tree. Typically this area extends to the dripline of the tree. The severing of one root can cause approximately 5-20% loss of the root system. A reduction of this area by greater than 30% can pose stability concerns for the tree.
• A slow release fertilizer eg: bone meal or approved equal to be applied to trees where root pruning or root damage has occurred. Apply per manufacturer’s recommendations.
• Roots over 2.5cm diameter that are to be cut should be pruned rather than left torn or crushed.
• At the commencement of construction prune roots cleanly using acceptable arboricultural practices and immediately backfill with appropriate material. The following are general methods of root pruning to be utilized when grading/construction will occur within the dripline of trees:
  1. Soil excavation using supersonic air tools, pressurized water or hand tools, followed by selective root cutting.
  2. Cutting through the soil along a predetermined line on the surface using a tool specifically designed to cut roots.
  3. Mechanically excavating (eg. backhoe) the soil and pruning what is left of the exposed roots.
  4. Cuts to be made with hand pruning shears, by-pass blade or pruning saw. Do not use anvil-type pruners.

Branch pruning practices

• All limbs damaged or broken during the course of construction should be pruned cleanly, utilizing by-pass secateurs in accordance with approved horticultural practices. Should there be a potential risk of transfer of disease from infected to non-infected trees; tools must be disinfected after pruning each tree by dipping in methyl hydrate. This practice is particularly important during periods of tree stress and when pruning many members of the same genera, within which a disease could be spread quickly (i.e., verticillium wilt on maples or fire blight on genera of the rosacea family).
• All pruning cuts should be made to a growing point such as a bud, twig or branch, cut just outside the branch collar (the swollen area at the base of the branch that sometimes has a bark ridge), and perpendicular to the branch being pruned rather than as close to the trunk as possible. This minimizes the site of the wound. No stubs should be left. Poor cut location, poor cut angle and torn cuts are not acceptable.
• Extensive pruning is best completed before plants break dormancy. Pruning should be limited to the removal of no more than one-third (1/3) of the total bud and leaf-bearing branches. Pruning should include the careful removal of deadwood, branches that are weak, damaged, diseased and those which will interfere with construction activity, secondary leaders of conifers, trunk and root suckers, trunk waterspouts, and tight v-shaped or weak crotches (included unions).
• The contractor must immediately report any damage to trees such as broken limbs, damage to roots, or wounds to the main trunk or stem systems so that the damage can be assessed immediately.
• The tree protection fencing will be maintained until all construction is completed, soils are stabilized and all of the equipment has been removed from the site.
• Any branches that overhang the work area and require pruning are to be pruned using good arboricultural practices utilizing by-pass secateurs in accordance with approved horticultural practices and/or American National Standard (ANSI) a300 (Part 1) – 2008 pruning

Tree Injury

• Typically tree roots extend 1.5 to 3 times beyond the dripline of the tree and are within the top 150mm of the soil. Types of damage from construction include:
  1. Physical injury
  2. Soil compaction
  3. Severing of roots
  4. Smothering of roots
  5. Split or broken branches
  6. Excessive pruning
• Soil compaction reduces pore space, oxygen available to roots increases carbon dioxide accumulation, restricts root growth and the ability to absorb water and nutrients, as well as impairs drainage.
• Smothering of roots: 90% of fine absorbing roots are within the upper 150-300mm of the soil. Smothering with the addition of soil can kill the roots and stress the tree. Physical injury, split or broken branches hinder the trees ability to compartmentalize (close) wounds properly.

Tree protection/mitigation notes

• The contractor must take the following steps when construction activity occurs within the tree dripline:
  1. Apply 150-300mm mulch or 150mm mulch and road masts on all areas of potential compaction (foot/vehicle traffic). See notes for ‘Work within a tree protection zone’ below for additional guidelines for working within the dripline.
  2. Prune damaged limbs with sharp disinfected blades. See ‘Branch pruning practices’ on this sheet.
  3. Water affected trees to field capacity within the entire dripline bi-weekly from June 1st to September 15th.
  4. Never store equipment/materials within a Tree Protection Zone. See ‘Tree Protection Zone’ section on this sheet.
  5. Contractor to adhere to the guidelines on this sheet.

Work within a tree protection zone

• If work must be conducted within a Tree Protection Zone the contractor should minimize soil compaction and mechanical root damage by utilizing one of the following four methods:
  1. Applying 150-300mm of mulch to area. Upon completion remove excess mulch leaving a 100mm depth layer of mulch.
  2. Laying 20mm thick plywood or 100x100mm wood beams over a 100mm thick layer of wood chip mulch. Upon completion remove plywood and leave mulch layer in place.
  3. Applying 100-150mm depth of gravel over a taut, staked geotextile fabric. Upon completion remove gravel and geotextile.
  4. Placing commercial logging or road mats on top of a mulch layer. Upon completion remove mats. Stone, geotextile and mulch exceeding 100mm thick will be removed from the Tree Protection Area once the threat of soil or root damage has passed.

Tree Protection Zone

• Applies to trees located within the limit of grading or noted otherwise. These trees are to be preserved and will have silt/tree protection fencing installed at along the limit of grading/limit of work to establish the Tree Protection Zone. Any damage to trees such as broken limbs, damage to roots, or wounds to the main trunk or stem systems are to be reported to the consulting arborist so that the damage can be assessed immediately and mitigation can be promptly implemented. Within a Tree Protection Zone there is to be:
  1. No construction
  2. No altering of grade by adding fill, excavating, trenching, scraping, dumping, or disturbance of any kind.
  3. No storage of construction vehicles, equiptment, soil, construction waste or debris within dripline
  4. No movement of vehicles/equiptment
  5. No parking of vehicles or machinery
  6. No digging or boring
  7. No rigging cables should be wrapped around or installed in tree
  8. No contaminants will be placed over root system
  9. No contaminants will be dumped or flushed where feeder roots of trees exist