Attachment 4. Arborists Report - Talbot Mackenzie & Associates
Arborist assessment detailing tree retention plans and mitigation of construction impacts for the development site.
Talbot Mackenzie & Associates Consulting Arborists
October 31, 2011
Seven Valleys Development LTD 725 Caleb Pike Road Victoria, BC V9B6G5
Attn: Tony Akhavan
Re: Lake View Village – Residential Development Proposal
Assignment: Prepare a tree retention plan to be used during the proposed construction of a mixed-use townhouse/condominium development on Lot C, Nursery Hill Drive.
Methodology: Each tree was identified onsite using its existing numeric tag number. Information such as tree species, size(dbh), critical root zone, health and structural condition, relative tolerance to construction impacts and general remarks and recommendations was recorded in the attached tree resource spreadsheet.
Potential impacts: We anticipate that the highest onsite impacts will occur during excavation, blasting and rock removal to create the footprint for the proposed townhouses, condos, parking areas and driveways.
Observations: At the time of our site visit all of the trees had been removed and a portion of the blasting work had been completed in the center of the property, leaving the trees along the back and sides of the property that have the best opportunity for retention given the proposed development plans. The ability to retain these perimeter trees will depend on their current health and structural condition and any impacts that are proposed for within their critical root zones. Douglas fir trees numbered 629 to 635 are located where they potentially could be retained given the proposed building and parking design. This group of trees is showing decline symptoms in the form of large deadwood, epicormic growth, limb failure and reduced annual shoot growth, likely due to impacts from the recent construction that has taken place on the neighboring lot and over all changes in hydrology and drainage patterns from the surrounding development. It is likely that these trees will continue to decline, regardless of the changes that are to occur on lot C and as they decline it will increase the risk of limb failure and eventually whole tree failure. In our opinion, given their existing health and structure, the impacts that are going to occur from the development on lot C and the introduction of new targets, it would be wise to remove these trees prior to construction and use this area to replant with healthy young native trees that can better adapt to these growing conditions.
Mitigation of impacts:
Barrier Fencing
Areas, surrounding the trees to be retained, should be isolated from the construction activity by erecting protective barrier fencing. Where possible, the fencing should be erected at the perimeter of the critical root zones. The barrier fencing to be erected must be a minimum of 4 feet in height and constructed of solid material or flexible safety fencing that is attached to wooden or metal posts. If a flexible fencing material is used, the top and bottom of the fencing must be secured to the posts by a wire or board that runs between these posts. The fencing must be erected prior to the start of any construction activity on site (i.e. demolition, excavation, construction), and remain in place through completion of the project. Signs should be posted around the protection zone to declare it off limits to all construction related activity. The project arborist must be consulted before this fencing is removed or moved for any purpose. Solid hording material may also be required to protect the trunks of trees from mechanical injury if vehicles or machinery are permitted close to tree trunks and where blasting is required.
Blasting and rock removal
We anticipate that further blasting will be required, in addition to blasting that has already taken place. Blasting to create the required grades for the condominium and townhouse units may necessitate the removal of bylaw-protected trees. Once the scope of the blast is defined, we can comment further on the potential impacts to the tree resource. If areas of bedrock are encountered, the blasting to level these rock areas should be sensitive to the root zones located at the edge of the rock. Care must be taken to assure that the area of blasting does not extend into the critical root zones beyond the building and road footprints. The use of small low-concussion charges, and multiple small charges will reduce fracturing, ground vibration, and reduce the impact on the surrounding environment. Only explosives of low phytotoxicity, and techniques that minimize tree damage, are to be used. Provisions must be made to store blast rock, and other construction materials and debris away from critical tree root zones. Should bedrock be encountered within service trenches that are located within the critical root zones of trees that are to be retained, alternate methods of removal that do not include explosive charges may be required.
Building footprint
Excavation for the proposed townhouse footprints will likely necessitate the removal of trees on the Southern side of the property. Trees that appear to be located within the building footprints according to the plans supplied include: 607, 609, 610, 611, 612, 613, 614, 615, 616, 622, 623, 625, 624, 626, 637, 638, 636, 640.
The following trees are located outside of the building footprints, but will be impacted; and in our opinion will be unsuitable to retain in a high target area: 634, 633, 632, 631, 635, 630, 629, 627, 619.
Trees that may be possible to retain providing that the critical root zones can be adequately protected: 646, 647, 628, 513, 606, 604, 608, 621, 620, 648, 605, 603, 602, 601, 617, 618.
Driveway/parking areas
The following trees will likely require removal for the proposed driveway/parking areas: 641, 642, 643, 644, 645.
Floating driveway specifications are recommended for any paved surfaces within the critical root zone of Garry oak #647. Approximately 90 percent of the critical root zone of this tree has been backfilled previously. If this backfill required removal for driveway construction, we recommend it be removed under the supervision of the project arborist. We recommend that if retained, this tree be examined more closely by an ISA certified arborist to determine if it a good specimen to retain in a high target area.
Servicing
From our discussions, it is our understanding that all servicing will come in off of Nursery Hill Drive, outside of the critical root zones of bylaw-protected trees. If proposed services encroach critical root zones of bylaw-protected trees, their locations must first be reviewed with the project arborist. Any excavation within the critical root zones of bylaw-protected trees must be performed under the supervision of the project arborist.
Stump removal
If stumps require removal within critical root zones of bylaw-protected trees, they must be removed under the supervision of the project arborist, or ground in place using a stump grinder.
Building/canopy conflicts
Once detailed building plans and elevations are made available, we can comment on pruning specifics. An ISA Certified arborist must complete the pruning of any bylaw-protected trees.
Lot D
During our site visit, it was noted that there have been tree failures throughout lot D. We recommend that trees within striking distance of the proposed development be examined for any evidence of wood decay pathogens. We also recommend that they be examined during high wind conditions for any evidence of root plate instability.
Work area and Material Storage
On restricted sites such as this, it may be difficult to find sufficient space for soil and material storage onsite without using portions of the defined critical root zone. If access within the critical root zone area is required for construction or material storage, the project arborist must be contacted to propose appropriate mitigation measures based on the degree of encroachment required.
Review and Site Meeting
Once the building permit is approved, it is important that the project arborist meet with the principals involved in the project to review the information contained herein. It is also important that the arborist meet with the site foreman or supervisor before any site clearing or other construction activity occurs.
Arborists Role
It is the responsibility of the client or his/her representative to contact the project arborist for the purpose of:
- Locating the barrier fencing or hording for tree protection
- Reviewing the report with the project foreman or site supervisor
- Locating work zones, where required
- Supervising excavation for the driveway and sidewalk footprints, and service corridor
Please do not hesitate to call us at 479-8733 should you have any further questions.
Thank You.
Yours truly, Talbot Mackenzie & Associates
Tom Talbot & Graham Mackenzie ISA Certified, & Consulting Arborists Encl. -- Tree Resource Spreadsheet, Barrier Fencing Specifications, Floating Driveway Specifications
Disclosure Statement
Arborists are professionals who examine trees and use their training, knowledge and experience to recommend techniques and procedures that will improve their health and structure or to mitigate associated risks.
Trees are living organisms, whose health and structure change, and are influenced by age, continued growth, climate, weather conditions, and insect and disease pathogens. Indicators of structural weakness and disease are often hidden within the tree structure or beneath the ground. It is not possible for an Arborist to identify every flaw or condition that could result in failure or can he/she guarantee that the tree will remain healthy and free of risk.
Remedial care and mitigation measures recommended are based on the visible and detectable indicators present at the time of the examination and cannot be guaranteed to alleviate all symptoms or to mitigate all risk posed.
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