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ARBORIST
REPORT
Date:
May 21, 2021
Prepared for:
Navdeep Gill
Site Address:
1825 NE 38th St
Renton, WA
Prepared by:
Tom Quigley
ISA Certified Arborist, PN-655A
Tree Risk Assessment Qualified (TRAQ)
Olympic Nursery, Inc.
P.O. Box 2013
Woodinville, WA 98072
tom@olympicnursery.com
www.olympicnursery.com
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NARRATIVE
Scope of Work
You have asked me to assess the current condition of four (4) trees located immediately north
of the excavation for the underground storm water vault. Specifically, you wanted an
assessment of the roots of said tree, as they may have been impacted as a result of the nearby
excavation.
Methodology
The methods and techniques used for this assessment are as outlined in Tree Risk Assessment
by Julian Dunster and as adopted by the International Society of Arboriculture (ISA). Additional
standards, practices and specifications are as detailed in ANSI Standard A300 (Part 9)-2017 Tree
Risk Assessment a. Tree Failure. The end goal of most assessments is to provide the owner or
manager of the tree(s) with factual information, enabling them to make decisions about the
management of the tree(s). For this particular assessment, I used a Level II Assessment that
includes inspection of the root collar, lower trunk, and canopy of the tree as can be seen from
the ground. Basic assessment does not include climbing the tree or excavation of soils to
inspect root structure or condition. However, in this case, excavated slopes were exposed and
were available for limited visual observation.
I measured each tree for its Diameter at Breast Height (DBH), an industry standard of
measuring trees at 4.5’ above grade. I estimated the dripline radius of each of the four trees
and made notes as to any specific conditions that were deemed noteworthy. Each tree was
assigned a ‘Condition’ rating on a scale of Poor, Fair, Good, Excellent. Condition ratings are
derived by considering the overall structure and vigor, as well as the growing conditions.
Findings and Observations
I visited this site in March of 2021 and again May 22, 2021. In March, the excavation near the
subject trees had not begun. The information in this report reflects the conditions assessed at
this most recent site visit.
There are four trees included in this assessment. They are numbered one to four (1-4)
numbered east to west or as a person would encounter the trees as they walk along the tree
protection fencing.
Tree #1 – This 18.2” DBH Douglas fir appears to be in Good condition. The root collar was not
visible though it appears this condition has been long-standing. The tree leans thirty-degrees
east but then is self-righted. The Tree Protection Fencing (TPF) is located just 4’ south of the
tree. There is an additional 4’ of undisturbed ground outside the TPF. There is a survey stake
marked “Clear Limits” that is located 6’ east of this tree but in-line with the tree. If the TPF had
been placed at the “Clear Limits”, the TPF would be against the tree trunk. The dripline extends
just beyond the excavation edge and is estimated at 14’.
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Tree #2 – This 18.3” DBH Western Red Cedar is located 6’ inside the TPF with an additional 6’ of
undisturbed ground outside the TPF. The tree is in Excellent condition. The dripline radius of
the tree in the south direction is approximately 18’.
Tree #3 – This 25.0” DBH Western Red Cedar is the dominant tree in this stand of four (4) trees.
It appears to be in Excellent condition with a 20’ radius dripline to the south. The TPF is located
9’ from the tree with an additional 8’ of undisturbed ground outside the TPF. The foliage of this
tree has dominated Tree #4. The dripline extends an estimated 20’ south.
Tree #4 – This 16.1” DBH Douglas fir is in Fair condition; its canopy has been dominated by the
Western Red Cedar, Tree #3. The TPF is located 10’ from Tree #4 with additional undisturbed
ground outside the TPF. This tree has a dripline of 24’ west but only 10’ south, again due to the
dominance of Tree #3.
Considerations
I’ve included two photos below that were taken May 22, 2021; taken from a forty-five-degree
angle to the north edge of the excavation pit and from the west end of the excavation pit.
These photos seek to document the soil conditions present at the time of this assessment.
Access to a closer advantage point was not possible due to site safety protocols for the steep
slopes of the excavation pit.
The photos document the lack of significant roots; roots that are larger than 2” in diameter or
large clumps of torn root ends. This is consistent with what would be expected from the size of
the trees and the distance from the tree trunk to the excavation cut. It is common to consider a
trees’ dripline as the optimal root protection zone. It is also common to provide adequate root
zone protection by allowing some intrusion inside the dripline, provide that the intrusion is
limited to a manageable amount of the entire root zone. When the intrusion is planned for one
side of the tree only, as is the case here, the accepted intrusion is usually capped at 50% of the
dripline radius.
The existing TPF is located closer to the Tree #1 and Tree #2 than the commonly prescribed 50%
of dripline radius. There is an additional area of between 4’ and 8’ outside of the TPF that has
not been disturbed, which is providing additional root zone protection, despite being outside of
the tree protection fenced area.
Conclusions
I do not see evidence of significant root system impacts in the excavation slope soils. Certainly,
there have been small feeder roots displaced and removed, for which the tree should be able to
compensate. It is likely that the trees will shed needles two to three years from now, a
response to the loss of feeder root mass. I believe the loss of structural roots has not been
significant and that the stability of the four trees has not been substantially altered. The four
individual trees enjoy the wind protection of growing in a ‘stand’ of trees. Their roots systems
are intermingled for additional support.
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All four trees would benefit from additional mitigation that should be adopted and planned for.
These mitigation measures include the following.
• The existing tree protection fencing is closer to Tree #1 and #2 than what is considered
optimal. As the vault is completed and the excavation pit is back-filled, care should be
given to protecting the now current edge of the excavation, in order to not disturb any
additional soils.
• If additional asphalt paving needs to be removed from inside the dripline radius of the
trees in order to complete the regrading around the vault, this work should be
monitored by a tree professional.
• As the work around the vault is completed, the TPF should be moved to reflect the drip-
line radius of each tree.
• Any exposed bare soil within the drip-line radius of each tree should be covered with 3”
of arborist wood chips or another commercial mulch product.
• If additional asphalt is removed and roots are exposed, further assessment should be
undertaken to asses any change in associated risk factors.
• These trees would benefit from additional summer-time hydration, as may be possible
for such large trees.
Two photos below.
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Taken May 22, 2021 from west end of excavation pit looking back at the
north edge and slope of the pit.
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North slope of excavation pit. Appears to be free of any torn roots or roots
larger than 1” – 2” in diameter.
This report was prepared by Thomas Quigley, ISA certified arborist PN0655A. Tree Risk
Assessment Qualified (TRAQ) by the International Society of Arboriculture (ISA).
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