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HomeMy WebLinkAboutTR_Arborist Report_190908_v1.pdf13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 July 23, 2019 Project: Pre-construction assessment for property re-development at 1073 Harrington Ave NE, Renton, WA. Parcel numbers 7227801315, 1310, and 1290. Contact: Brent Chastain - Third Place Design 341 NE 91st Street Seattle, WA 98115 Phone – 206 920 9996 Email – Brent@thirdplacedesigncoop.com Objectives: Evaluate health of existing trees and establish criteria for the preservation of those to be retained. Description: The proposed development is formed from a modified combination of six previous lots which the Renton Housing Authority purchased between 2011 and 2014 (Figures 1 and 2). Until 2015 five properties had numerous trees present, mainly along the lot lines (see Figure 2). The same canopy configuration goes back at least twenty years as shown in Figure 3. The City of Renton had the existing houses demolished in 2016. Post demolition the tree cover was reduced by roughly sixty percent and the area bulldozed where the houses had been (Figure 4). The RHA is now ready to proceed with developing the site and contracted with Third Place Design. Their proposed site plan is shown in Figure 5. They in turn contacted Superior NW and asked that a formal assessment of the remaining tree be made. The provided plan shows a large evergreen in the center of the development and four others on the west side that currently exist. There are a number of trees shown which will be installed post construction. The following itemized list begins in the northwest corner of the property. It includes the trees currently on the property and those within 10’ of the borders. The numeric designations are reflected in the tree plot shown in Figure 6. The diameters measured were taken at the standard height of 54” above grade (DSH) and the trees were tagged with 1” green circular markers. 1) Douglas Fir (Pseudotsuga menziesii) 26.5” DSH, 25’ tall standing 10’ E of the rough curb line/parking area along Glenwood Avenue and 16’ S of the NW corner marker. The tree has been topped multiple times for power line clearance (Figure 7). It has a full canopy which descends to near the 10’ level. The branches are somewhat overextended and are encroaching on a utility pole in its NW quadrant as shown in Figure 8. It has good new growth and color. Enterprises 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 2) Douglas Fir 29” DSH, 70’ tall standing 65’ S of the #1 tree and 8’ E of the rough curb line. It is in fair condition with average new growth and color. There is some deadwood present and it has been pruned multiple times for power line clearance on its west face. Its canopy extends down to the 12’ level. The SW corner of the previous house was less than 15’ away from the base of the tree and the driveway ran fully beneath its canopy as shown in Figure 9. 3) Douglas Fir 24” DSH, 65’ tall standing 36’ S of #2, 8’ E of the rough curb line, and at the north end of a small stand. It is in fair condition and its canopy extends down to the 12’ level although it mainly extends to north and is slightly over extended. There is ivy present in the tree. It has been pruned for wire clearance multiple times. The NW corner of the previous house was around 15’ back from the tree and its driveway ran beneath the tree. 4) Douglas Fir 17.5” DSH, 65’ tall standing 4’ SW of the #3 tree. All its canopy extends to the west except for at the very top. It has somewhat limited new growth and decent color. It has been pruned multiple times for wire clearance. There is ivy present in the tree. 5) Douglas Fir 18” DSH, 60’ tall standing 7’ S of the #4 tree. There is not much canopy on this tree. Most of it is on the east side in a narrow column and then there is a little foliage on the west side starting at the half way point and running nearly in a single branch width. It has noticeably limited new growth and poor color. It has been pruned multiple times for wire clearance. There is ivy present in the tree. A crow’s or hawk’s nest is visible at the very top. 6) Douglas Fir 25” DSH, 65’ tall standing 5’ S of #5, 8’ E of the existing edge of the asphalt for Glenwood Avenue, 24’ N of a set of new water meters, and at the south end of the stand. It has fair color but below average new growth. Its canopy extends down to the 12’ level, almost entirely extends to the south, and is slightly over extended. There is ivy present in the tree. It has been pruned for wire clearance multiple times. The west side of the previous house was close to 20’ back from the tree. 7) Silver Maple (Acer saccharinum) 40” DSH, 55’ tall, 28’ radial spread standing 65’ nearly due east of the #2 fir. The tree is in decline with poor color, stunted new growth, deadwood and die back throughout the canopy, and it is already showing color changes at the extremities. It has a cavity low on the west side with a 7” diameter opening. The previous house was 25’ west of the maple’s base. There had been several smaller trees or quite large shrubs standing between this tree and the #8 fir to its east prior to the demolition event as shown in Figure 2. 8) Douglas Fir 28” DSH, 70’ tall standing 55’ ESE of the #7 maple. The top of the tree was damaged near the 55’mark and it now exhibits multiple stems above that level (see Figure 10). It has average new growth and color. There have been recent breakouts along the SE quadrant probably due to snow loading. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 9) Pacific Dogwood (Cornus nuttalli) 13” DSH, 35’ tall, 9’ spread standing near the center line on the south side of the parcel. The tree is in weak condition with little to no new growth and poor color. An 8” caliper branch cracked out low on the stem and tore into the quick of the tree. Another 6” caliper branch broke out about 18” higher on the stem. The tree is nearly engulfed in English Laurel and holly. 10) Red Alder (Alnus rubra) 36” DSH, 45’ tall, 25’ spread standing 45’ W of the #9 tree at the south end of the parcel. It has advanced decay present along the column and the main scaffolds. The upper half of the canopy is dead. Before the demolition event this tree was surrounded by a dense thicket of other shrubs/small trees. Currently there is nothing around the tree but grass and weeds. Methods: Tree assessment is both an art and a science. To properly perform, an arborist must have an extensive background in biology, tree mechanics, and tree structure that is equal parts academic and field knowledge. It takes years of study to recognize and correctly diagnose the subtle signs trees exhibit before their failure, whether it be partial or total. The process begins with a visual inspection (visual tree assessment, VTA) which is followed up as necessary with soundings, core testing, and/or other detection means. Each tree is examined and evaluated according to several factors including species type, size, vigor, injuries present, root and grade disturbance, deadwood, location and extent of decay, stem taper, exposure, and targets that are at risk. Discussion: Of the ten trees listed only the #3-6 and #8 firs are noted for retention. The other trees currently present are located in areas which will be occupied by structures. The #8 Douglas Fir is shown in Figure 5 with a 20’ radial space (a little more in the NE and SW quadrants) left within which it is to live. Trees can accept some loss of rooting space and still survive but the arboricultural industry accepted threshold is thirty percent. In the given scenario the tree will lose over 50% of its Critical Rooting Area. If the tree is meant to be a long term asset for the campus then this area has to be increased to at least a 23.5’ radial circle. This could be accomplished by making the pathways around the tree fully permeable. Pre-grading and excavation a hard fence will have to be set up around this tree at a distance of 25’ radial feet. The area within the fence should be covered with 6-8” of arbormulch. When it is time to do the improvement work within the fencing (the paths, the parking, the corner of Building B East’s foundation forms) it will have to be overseen by an arborist to document the degree and nature of the impact. The path should be cut and set by hand if in any way possible. All the mulch would be left around the tree once construction is finished. No grass should be planted. The only plants which should be installed would be those commonly found around firs naturally. Salal, evergreen or deciduous huckleberries, rhododendron species, vine maples (native or Japanese varietals), and the like would be acceptable choices. The top of the tree will have to be pruned to create a stronger long term structure. Depending on what the climbing arborist finds it could be that the tree will need ongoing care on a five to seven year basis. The tree would definitely benefit from a deep root feed at the end of the construction process to help it cope with impact stress. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Based on the historical imagery shown in Figure 2 it is clear that the #3-6 firs incurred root disturbance well within their Critical Root Zones (CRZ). This is the area defined as one radial foot per inch of tree diameter. Trenching type incursion, that is excavation that occurs along only one sector of a tree’s CRZ, can reach significantly into the root growth area without having a detrimental long term effect. What does have to be absolutely protected is a tree’s Structural Root Plate (SRP). This radial area is related to the diameter inches of the tree in question but not quite in such a direct proportion. Figure 11 below illustrates the relationship. Figure 11. Size of the Structural Root Plate in relation to tree stem diameter. Note that the SRP levels off at 10’ for any tree over 24” in diameter (Coder, 1996). In the case of the four firs mentioned above, the excavation of the existing house’s foundation on their east side occurred between 12’ and 17’ from their bases. This would have been well outside any of the fours’ SRP. The proposed walkway to their north is 20’ away; again well outside the SRP for the #3 tree. The new foundation work for Building B West could come as near as 18’ to the base of the trees. This will still not affect the Structural Root Plates of any of the four trees. However, if the City of Renton is going to ask that a sidewalk is installed on the west side of the trees or that any other hardscaping improvement be made which requires a change in grade, these trees will be severely impacted. Installing sidewalk will necessitate the removal of all four due to compromising their structural stability. Any other improvements on the west side will have to be evaluated on a case by case basis. Protection fencing for the stand should be set at the full CRZ distance for the larger two, namely twenty-five radial feet on three sides. On the west it will have to be limited to being at the curb line or just slightly beyond as traffic safety dictates. The area within the protection fencing should be filled with 6-8” of arbormulch and arborist oversite is dictated when work has to occur within the protection zone. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Waiver of Liability Because the science of tree risk assessment is constantly broadening its understanding, it cannot be said to be an exact science. Every tree is different and performing tree risk assessment is a continual learning process. Many variables beyond the control, or immediate knowledge, of the arborist involved may adversely affect a tree and cause its premature failure. Internal cracks and faults, undetectable root rot, unexposed construction damage, interior decay, and even nutrient deficiencies can be debilitating factors. Changes in circumstance and condition can also lead to a tree’s rapid deterioration and resulting instability. All trees have a risk of failure. As they increase in stature and mass their risk of breakdown also increases, eventual failure is inevitable. While every effort has been taken to provide the most thorough and accurate snapshot of the trees’ health, it is just that, a snapshot, a frozen moment in time. These findings do not guarantee future safety nor are they predictions of imminent events. It is the responsibility of the property owner to adequately care for the tree(s) in question by utilizing the proper professionals and to schedule future assessments in a timely fashion. This report and all attachments, enclosures, and references, are confidential and are for the use of Brent Chastain, Third Place Design, the Renton Housing Authority, and their representatives only. They may not be reproduced, used in any way, or disseminated in any form without the prior consent of the client concerned. Anthony Moran, BS Certified Arborist Qualified Tree Risk Assessor ISA #PN-5847A 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 1. New parcel configuration. Figure 2. Aerial view of the six lots circa 2015 showing prevoius configuration. Note the concentration of trees along the perimeter of the properties. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 3. Aerial view from 2000 showing nearly the same canopy coverage. Figure 4. Aerial view circa 2017 showing the new parcel post demolition. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 5. Concept of site redevelopment. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 6. Current aerial view of subject property. The white numerals correspond to the nomenclature in the description section and show rough placement of the indicated trees. Please refer to the most recent survey for exact locations. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 7. Photo of the #1 Douglas Fir taken during the July 2019 site visit. Figure 8. Photo of the #1 fir showing encroachment on the utility pole at the NW corner of the parcel. 13110 NE 177th Place #304 * Woodinville, WA 98072 * Anthony@SuperiorNW.com 206-930-5724 Figure 9. Enlargement of the 2015 aerial photo showing driveways running under the #2 and #3 firs. Figure 10. Photo of the top of the #8 fir showing the weak structural formation.