14546 Tree Protection Plan.pdf

Tree Protection & Preservation During Construction:

OPRD Standards and Specifications

Trees on Oregon Parks and Recreation Department (OPRD) property are a valuable asset to our visitors and the Department as a long-term natural resource value providing wildlife habitat, outstanding aesthetics, water retention and many other quality environmental factors. It is possible to preserve the longevity of trees on building sites if the right measures are taken. The most important step is to utilize a professional arborist during the planning stage. An arborist can help you decide which trees can be saved, and can work with the builder to protect trees throughout each construction phase.

SECTION 1.0. TREE REPORTS.

An arborist report is needed for development projects where trees may be impacted by construction activity. The report must be prepared by a certified arborist for the purpose of providing accurate information and opinion regarding the condition, welfare, maintenance, preservation or value of a protected or designated leave tree.

A. All Tree Survey Report - All Tree Survey Report shall contain the following information: A tree inventory which includes species, size (greater than 4 inches in diameter), condition of tree health and structural integrity, decay, soil limitations, imminent danger of falling, recommendations and rated for suitability for preservation with the designated project area.

B. Protected Trees Report - Trees rated for preservation shall be included in a “Protected Tree

Report” and shall contain diagram of tree(s) location; perimeter of leaf canopy; proximity to roads, developed paths, structures, etc. and tree protection instructions (if needed).

SECTION 2.0. TREE PROTECTION AND PRESERVATION PLAN.

All protected or designated retention trees on the development site shall be shown on approved sets of civil, building and landscape plans and shall be protected during the construction process. A Tree

Protection and Preservation Plan is required when retention trees may be injured by disturbance. The

Tree Protection and Preservation Plan shall assume compliance with the following standards in Section

3.0, Tree Damage Occurrence and Mitigation:

A. Scope & Construction Phasing - The Tree Protection and Preservation Plan shall at minimum contain written recommendations for the health and long-term welfare of retention tree(s) during any of the following stages of construction; pre-construction, demolition, construction, site plan changes, post-construction. Recommendations shall include but may not be limited to the following; tree injury avoidances practices, allowed and prohibited practices around retention trees, and damage treatment practices, if and when they occur.

B. Tree Protection Zone (TPZ) - The Tree Protection and Preservation Plan shall establish a TPZ, (a fenced off area) around each tree marked for preservation. The TPZ shall clearly outline site-specific measures for protection of tree(s) during construction as well as guidance for continued tree maintenance, post-construction. Additionally, once the project has received final approval, any changes to the Tree Protection and Preservation Plan, shall be approved by OPRD

Forester/Arborist. See Sections E-G for TPZ standards.

C. Site Plan Must Show Tree Protection - Site plans submitted for demolition, grading, construction, and other operations relevant to the project, shall provide illustrated diagrams of protective tree fencing areas. Additionally, the diagrams shall identify the areas of protective tree fencing as a bold dashed line.

D. Pruning - In order to avoid damage during construction, the lower limbs of retention trees shall be inspected for clearance, prior to beginning construction activities. Trees which require pruning prior to construction shall be done so follow the (ANSI A300 (Part 1)-2001 Pruning Standards.

Pruning of green limbs shall be minimized to the extent possible.

SECTION 3.0. TREE DAMAGE OCCURRENCES AND MITIGATION.

A. Physical Injury - Construction equipment can injure the above ground portion of a tree by breaking branches, tearing bark, and wounding the trunk. These injuries are permanent, and if extensive, can be fatal. Damage which occurs to retention tree(s) may be subject to fines as outlined in Section 5.0, Infraction of the Specifications, if damage exceeds the following specifications;

1. For Broken Branches – When the number of branches broken by Contractor exceeds 20 percent of the total live crown.

2. For Trunk Damage – When damage exposes the cambium layer of tree in an area greater than thirty-six square inch.

3. For Root Damage – When more than one anchor root is severely damaged or severed.

B. Root Protection – The tearing and ripping of roots by digging and trenching, necessary for a construction project, will likely occur at some point. The amount of damage a tree suffers from root loss depends, in part, on proximity to the tree trunk.

Subsurface Construction – Generally two types of subsurface construction may be utilized when placing underground infrastructures such as water and electrical pipes. These types of construction are 1) Directional Drilling, also known as Horizontal Directional Drilling and 2) Open-cut Trenching. Although Directional Drilling is always the preferred method for optimal tree root protection during operations, below is an outline of protection measures that should be utilized in either situation.

DIRECTIONAL DRILLING

1. Entry and Exit Pit Specifications - The most invasive part of directional drilling is the excavation of the launch and reception pits.

a. Location: All entry and exit pits must be located outside the TPZ/RPA of the protected trees.

https://files.oprd.oregon.gov/index.php/s/M2CckAAgRmxoTzP

b. Vacuum Excavation: If a pit must be located near the edge of a TPZ, use "soft dig" methods like Air Spade or vacuum excavation to expose roots without severing them.

c. Root Management: Any roots over 2 inches encountered in the pits should be preserved. If cutting is necessary, use sharp, sterilized hand tools to make a clean 90° cut. Never tear roots with backhoe buckets.

2. Drilling Depth and Path Requirements - The goal is to bore deep enough to stay below the

"active rooting zone," where the majority of water-absorbing roots reside.

a. Minimum Depth: The drill path must maintain a minimum depth of 24 to 36 inches when passing under the canopy of a protected tree.

3. Ground and Trunk Protection - If equipment (the drill rig or support trucks) must drive over the TPZ to reach the entry point:

b. Ground Matting: Lay down 6 inches of woodchip mulch covered by heavy-duty plastic

"swamp mats" or 3/4-inch plywood to distribute the weight and prevent soil compaction.

c. Trunk Wrapping: If equipment must operate within 5 feet of a trunk, wrap the trunk in

2x4 timber planks cushioned by foam or burlap, or similar materials to prevent mechanical "skinning" of the bark.

OPEN-CUT TRENCHING

1. Trenching Proximity to Tree Trunk - Use the following table as a guideline for subsurface construction activities in proximity to retention trees, when possible.

Table 1. Minimum Distance to Trench Trees.

TREE DBH MINIMUM DISTANCE FOR TUNNELING/TRENCHING

Less than 6 inches Drip-line of tree

6 to 9 inches 5 feet

10 to 14 inches 10 feet

15 to 19 inches 12 feet

More than 19 inches 15 feet

2. Root Pruning - Severing a single major anchor root can cause the loss of 5-20 percent of the root system. If needed to facilitate construction around a retention tree, no more than one anchor root shall be cut. When roots greater than 2-inches in diameter are encountered during digging or trenching activities, prune root with a clean pruning saw.

The cut shall be smooth and even, free of jagged edges or tears along the residual root.

C. Soil Compaction - Soil compaction can significantly reduce soil pore space, which is essential for adequate root growth and development. To prevent soil compaction in these areas, the use of equipment within the TPZ of protected trees shall be strictly limited or prohibited. Furthermore, equipment and materials shall not be stored in these areas, as this can also contribute to soil compaction.

D. Grade Changes –

1. Increasing the Grade – - 90% of water and mineral absorbing roots reside in the upper 6-

12 inches of soil. Avoid piling soil over root systems or near the dripline of retention tree(s).

2. Decreasing the Grade - Cutting away soil from a tree removes a portion of the root system and changes the soil moisture level. For reasonable survival, reduce or eliminate cuts within tree(s) drip-line. To preserve tree(s) roots, construct a retaining wall at the drip line or farther out (Figures 1 and 2).

3. Preventing Smothering Roots - Build a retaining wall at the drip-line to keep soil from burying tree roots. It is possible to completely cover the roots by using expensive drainage and venting techniques that require professional design and installation. Although it is easier, cheaper, and more practical to alter grading plans than it is to protect a tree from fill over the entire root-zone.

Figure 1.

In Figure 1, the change in grade has eliminated half of the tree's roots. Most trees will die from the extent of this injury.

Figure 2.

The tree on this cut-bank has been protected by a constructed wall at the drip-line. This tree should recover nicely.

E. Tree Protection Barriers - As the ability to repair construction damage to trees is limited, protection is vital to prevent injury to retention trees. When feasible, fencing or a physical barrier shall be placed around entire retention tree. The fence or barrier shall be placed as far from the tree trunk(s)as possible. use the following table as a guideline for erecting barriers around retention trees.

Table 2. Minimum Distance Erect Barriers from tree trunk.

TREE DBH MINIMUM DISTANCE FROM TREE

Less than 6 inches Drip-line of tree

6 to 9 inches 6-9 feet

10 to 14 inches 10-14 feet

15 to 19 inches 15-19 feet

20 inches or greater The greater of 20 feet or 10 feet beyond drip-line of tree

If the area cannot be fenced off, it shall be covered with 8-inches of wood chips which shall be remove at the completion of construction efforts.

F. Fenced Area(s) - The fenced area must remain clear of building materials, waste, and excess soil.

No digging, trenching or other soil disturbance shall be allowed within the fenced area.

G. Limiting Access – When feasible, allow only one access route onto and off-of project site. Access and contractor vehicle parking area instructions shall be provided. Specific storage areas, away from protected trees, shall be designated for; equipment, soil, and construction materials. Each sub-contractor must be made aware of; barriers, limitations, and specific work zones. Posting signs is recommended.

SECTION 4.0. INSPECTION AND ASSESSMENT.

OPRD Forester/Arborist or contracted arborist shall conduct site visits to accomplish simple visual inspections, insuring specifications and tree preservation measures are followed. Clear and concise objectives with the arborist and builder shall be communicated and passed onto all sub-contractors.

Construction damage to trees is often irreversible however, any retention tree(s) sustaining injury from the construction process may require remedial treatments that the arborist may suggest.

SECTION 5.0. INFRACTION OF THE SPECIFICATIONS.

A. The severity of an infraction will be proportional to potential damage to the retention tree(s), as stipulated in Section 3A. If an infraction is determined to have occurred, then Contractor may be liable to a fine proportional to the damage that has occurred and as stipulated below;

1. For Broken Branches – A fine of $500 may be solicited to Contractor when broken branches exceeds 20 percent of the total live crown of tree(s).

2. For Trunk Damage - A fine of $100 multiplied by each thirty-six square inch area damaged may be solicited to the contractor.

3. For Root Damage – A fine of $500 may be solicited to Contractor when more than one anchor root is severely damaged or severed.

B. If a protected retention tree is damaged to the point of imminent decline the basic tree value will be determine using the trunk formula method from the Guide for Plant Appraisal,10th Edition.

C. If more than 10 percent of the TPZ is covered in an added soil layer, removal (by hand shovel) will be required.

D. Drainage issues determined to be detrimental to protected tree(s) shall require correction.

E. If more than 10 percent of the TPZ is compacted, radial aeration with an air spade shall be required.

F. Photos and records may be taken at each stage of construction to help determine liability.

SECTION 6.0. POST-CONSTRUCTION.

Construction impacts to trees are often not immediately visible and can manifest over time. It may be months or even several years before a tree shows symptoms of decline from construction impacts.

Additionally, trees stressed from construction impacts are more prone to health problems such as disease, insect infestation, sun scald, and other site disturbance impacts. Retention trees should be evaluated periodically by a certified arborist to measure potential decline, and monitor hazardous conditions.

Additionally, site conditions should be assessed for proper drainage in case of changes from the construction project. Drainage problems may cause trees to decline rapidly. Ensure surface water drains away from trees and correct if needed.

Mulching can be one of the most effective enhancements after disturbance around tree(s). A three to four-inch layer of mulch should be placed around tree(s) as far from trunk(s) as is practical. This enhancement will be required if OPRD Forester/Arborist determines it necessary.

https://www.isa-arbor.com/Newsroom/determine-the-value-of-trees-with-the-guide-for-plant-appraisal