HomeMy WebLinkAboutTR_Arborist Report_180807_v1Arborist Report
City of Renton
May Creek Trail Extension Arborist Report
August 7, 2018
Submitted to:
Vanessa Dolbee
Current Planning Manager
1055 South Grady Way
Renton, WA 98057
Prepared By:
Otak, Inc.
11241 Willows Road NE, Suite 200
Redmond, WA 98052
Project No. 32978
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TABLE OF CONTENTS
Page
Summary of Findings .................................................................................................... 1
Assignment .................................................................................................................... 5
Observations ................................................................................................................. 6
Recommendations ........................................................................................................ 6
Figures
Figure 1 – Tree Map .............................................................................................................................. 3
Figure 2 - Site Aerial with site outlined with white dashed line (King County Parcel Viewer) ............... 5
Images
Image 1 ................................................................................................................................................. 7
Image 2.................................................................................................................................................. 8
Image 3.................................................................................................................................................. 9
Image 4................................................................................................................................................ 10
Image 5................................................................................................................................................ 11
Image 6................................................................................................................................................ 12
Image 7................................................................................................................................................ 13
Image 8................................................................................................................................................ 14
Tables
Table 1—Tree Table ............................................................................................................................. 1
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Summary of Findings
The tree risk assessment for the site discovered no high risk or extreme risk trees, part of the reason for
this is lack of proximate targets. Tree #324 has a forked trunk at approximately 35 feet above grade and
one trunk extends northeast. The attachment appears strong, however there are branches which could
potentially fall onto the overhead power lines along the west side of Jones Avenue NE. Table 1, below,
lists the significant trees onsite.
Table 1—Tree Table
Tag # Species Name Common Name Size
(DBH)
Health Notes
301 Alnus rubra Red Alder 36” Good
302 Alnus rubra Red Alder 12” Fair 40% LCR
303 Alnus rubra Red Alder 24” Poor 10% LCR
304 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
18” Good
305 Acer
macrophyllum
Bigleaf Maple 48” Fair Basal cavity
306 Alnus rubra Red Alder 20” Poor 5% LCR
307 Alnus rubra Red Alder 32” Poor 8’ split at trunk with
cavity
308 Alnus rubra Red Alder 16.5”
(7+15)
Poor 30% LCR
309 Alnus rubra Red Alder 16” Poor 20% LCR
310 Alnus rubra Red Alder 11” Poor One of three stems
alive with 20% LCR
311 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
45” Good
312 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
20” Fair No buttress roots
extending to north
313 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
32” Good
314 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
36” Excellent
315 Alnus rubra Red Alder 15” Good
316 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
34” Good
317 Salix lucida ssp.
Lasiandra
Pacific Willow 12” Fair
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Tag # Species Name Common Name Size
(DBH)
Health Notes
318 Acer
macrophyllum
Bigleaf Maple 35” Good
319 Alnus rubra Red Alder 26” Poor 12’ co-dominant
split/peel to grade
with cavity
320 Alnus rubra Red Alder 13” Poor 30% LCR
321 Acer
macrophyllum
Bigleaf Maple 48” Good
322 Acer
macrophyllum
Bigleaf Maple 44” Excellent
323 Acer
macrophyllum
Bigleaf Maple 40” @
12”
above
grade
Good Four stems forking
at 24” above grade
324 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
54” Good
325 Robinia
pseudoacacia
Black Locust 18” Fair Fork at 8’ has
included bark with
stems touching for
6’
326 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
14” Good
327 Robinia
pseudoacacia
Black Locust 13.5”
(12+6)
Good
328 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
13” Good
329 Populus
trichocarpa ssp.
Balsamifera
Black
Cottonwood
9” Good
330 Alnus rubra Red Alder 10” Fair Overhead power
line clearance
pruned
331 Alnus rubra Red Alder 13” Fair Overhead power
line clearance
pruned
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Figure 1 – Tree Map
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Assignment
The assignment is to provide an arborist report for the project site, in conjunction with 30% design plans
for the trail engineering and stream buffer mitigation.
The arborist report inventories all significant trees on-site. Per RMC 4-11-200, a significant tree is a “tree
with a caliper of at least six inches (6"), or an alder or cottonwood tree with a caliper of at least eight
inches (8"). Trees qualified as dangerous shall not be considered significant. Trees planted within the
most recent ten (10) years shall qualify as significant trees, regardless of the actual caliper.”
Tree species were identified, along with the size and a general characterization of health. Tag numbers
correspond to the round aluminum, pre-numbered tags affixed between six and eight feet above grade.
Size was measured as diameter at breast height (DBH) at 54 inches above grade, with multiple stems
either using a lower height above grade or square rooting the sum of the squared stem diameters, as
appropriate. Health ranges include excellent, good, fair and poor, with notes typically qualifying the rating
with approximate live crown ratio (LCR). Dead trees on-site do not appear on the table. Notes were
added to provide some context for fair or poor health trees.
The site is indicated below using a dashed white line. The site is approximately 1.9 acres in size and is
located due west of 4024 Jones Ave NE, Renton, WA 98056. The site is undeveloped. A six to eight-foot
wide trail is proposed for the site.
Figure 2 - Site Aerial with site outlined with white dashed line (King County Parcel
Viewer)
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Observations
On September 10, 2018, Tom Early conducted the site visit. Native red alder and black cottonwood trees
are the predominant tree on-site with black locust being the only non-native found. There are no conifers
on-site. Most of the alders are in decline, while the black cottonwoods are strongly growing.
Himalayan blackberry covers approximately 85% of the site, with the remainder occupied by reed
canarygrass and Japanese knotweed. Native understory shrubs, or groundcover, were not on-site but
were observed to the north and on the opposite bank of May Creek.
The site is currently traversed via a desire path through the blackberry which allows visitors to travel
underneath I-405 and continue westward toward Lake Washington. There is a newly developed trail with
benches and restoration planting in the parcel to the west of I-405. The use of the subject site is rare.
There were no high or imminent risk trees on-site. This is because there are no targets near the poor
health trees. The only tree which is entering the realm of tree risk is tree #324. It has a forked trunk at
approximately 35 feet above grade. While the attachment looks strong now, it may have some decay at
this union. One of the stems would likely fail to the northwest, into the overhead power lines which run
north and south along the west side of Jones Ave NE. There are some large limbs which might fail due to
sudden limb drop, but they are more likely to fail away from the overhead power lines than into them.
Recommendations
Removal
Two trees are recommended for removal, the two black locust trees, trees #325 and 327. These two trees
are recommended for removal to reduce the potential for a grove of black locust establishing on-site. The
black locust is characterized for its quick growth, ability to emerge in poor soils, and a large quantity of
viable seed. It is listed as a “weed of concern” in King County.
The other trees on-site are recommended for retention, even the dead and declining trees. They are all
native to the Pacific Northwest, consisting of red alder, black cottonwood and bigleaf maple. Many of the
declining trees may be considered unsightly, but they are performing habitat enrichment as standing
wildlife snags.
Protection
A five-times multiplier of the tree DBH as the radius dimension is suggested for placing the tree protection
fencing on this project. For example, an 18-inch DBH red alder would have tree protection fencing placed
7.5 feet away from its trunk. This is less than typical. Tree protection fencing will be located within the
dripline of most significant trees. Some compaction and disturbance of the root zone will occur outside of
the designated tree protection fencing due to trail grading and noxious weed removal. The amount of
compaction is unlikely to become detrimental to the healthy trees. Within the tree protection fencing area
removal of noxious weeds and grading shall be by hand. Clearing and grubbing along with grading for the
trail is minimal and unlikely to detrimentally harm the nearby trees.
The project components include constructing a six-foot wide trail, removing noxious weeds and planting
native trees and shrubs for stream buffer mitigation, placing a four-inch layer of arborist mulch throughout
the site, and installing a temporary automatic irrigation system. The mitigation planting is proposed to be
irrigated with a temporary automatic irrigation system. To balance reducing vandalism of the irrigation
system and tree impacts caused by the irrigation installation, it is suggested that the main and lateral
irrigation lines are above grade but descend below grade at valve boxes and at sleeves beneath Jones
Ave NE and the new trail. Tree protection fencing should remain in place through noxious weed removal,
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trail grading and trail construction. Tree protection fencing may be removed prior to temporary irrigation
installation, arborist mulch installation, and planting. This will ease the construction effort while still
minimizing the detrimental impacts on the root zone of the trees.
Tom Early, PLA #1199 Washington State, PN-5622A with tree risk assessment qualification.
Images
Image 1: arrows indicate trees #301, 302 and 303 from right to left, image is looking west
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Image 2: arrows indicating trees #304 and 305 on left and right, image is looking east
along desire path
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Image 3: tree #307 showing tree tag and split trunk
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Image 4: arrows indicating dead alder not included in inventory and trees #308, 309
and 310 from left to right, image is looking west along desire path
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Image 5: arrows indicating trees #314, 313, 312 and 311 from left to right, image is
looking northwest near tree #320
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Image 6: tree #321, image is looking southwest near tree #327
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Image 7: tree #322, image is looking west near tree #324
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Image 8: trees #331, 330, 329, 328, 325 and 326 from left to right, panoramic image is
looking west from Jones Ave NE