Loading...
HomeMy WebLinkAbout20-Arborist Report December 12, 2016 Project: Pre-construction assessment for lot development at 16433 and 16451 111th Avenue SE, Renton, WA. Parcel numbers 0088000570 and -560. Contact: Jonathan Murray - D. R. Strong Consulting Engineers, Inc 620 7th Avenue, Kirkland, WA 98033 Phone – 425 827 3063 Email – jonathan.murray@drstrong.com Objectives: Evaluate health of existing trees and establish criteria for their preservation. Description: This is a pair of midsized parcels, each close to 40,000 square feet, tucked in the middle of a row larger lots in the Renton Higlands (Figures 1-3). Each property has an existing home on the east end, the 16433 home was built in 1952, and the 16451 home in 1966. The 16433 parcel is lightly treed and no significant changes have occurred on it over the last twenty years. The 16451 parcel was fairly well covered with trees until 2009 when it was partially cleared. It was totally cleared by 2012. There is a wire fence running between the 16433 property and the 16411 property to the north. Another wire fence runs along the west end of 16433 and ties into a wood fence at the west end of the 16451 property. The wood fence runs nearly the entire width of the property, stopping about 5’ short of what appeared to be the SW corner of the 16451 parcel. Another wire fence runs east from that corner to about even with the back of the house. Both existing homes will be razed. According to the proposed development plans each parcel will be subdivided into five lots. A new home will be built on each save the east end of the 16451 parcel which will have a water retention area (Figures 4 and 5). The following itemized list begins at the SE corner of the 16433 property and runs roughly counter clockwise through the two parcels. Each tree was tagged and their numerical designations are reflected in Figures 3-5. Diameters were measured at the standard height of 54” above grade (DSH) during the December 2016 site visit. Heights were estimated. The majority of the trees described are shown on the November 2016 Short Plat. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 1) Weeping Willow (Salix babylonica) 26.5” DSH, 22’ tall, 14’ spread standing just to the right side of the south entrance to the 16433 property. The tree is in weak condition. It has been topped repeatedly and has multiple atrophied and decayed areas. 2) Scots Pine (Pinus sylvestris) 18” DSH, 30’ tall in fair condition with average new growth and color. Standing at east end of line at south end of the house. 3) Scots Pine 16” DSH, 32’ tall in fair condition with average new growth and color. Next tree west of #2. 4) Scots Pine 16” DSH, 35’ tall in fair condition with average new growth and color. Next tree west of #3. 5) Scots Pine 10.5” DSH, 25’ tall in weak condition with below average new growth, poor color, and signs of needle blight. Next tree west of #4. 6) Douglas Fir (Pseudotsuga menziesii) 10.5” DSH, 20’ tall standing just north of the end of the line of pines. Tree is dead. 7) Douglas Fir 12.5” DSH, 22’ tall standing at the SW corner of the 16433 house. Tree is dead. 8) Ash (Fraxinus sp) 19” DSH, 30’ tall, 14’ spread standing in line with and north of the #7 tree. It is in poor condition with a significant decay column running from the base to where it was topped near the 12’ level. 9) Douglas Fir 15” DSH, 26’ tall standing north of #8. It is in fair health but bifurcates at the 9’ mark and has an active fracture plane. May have been topped. 10) Douglas Fir 14” DSH, 28’ tall standing north of #9. It bifurcates at the 6’ mark and has an active fracture plane. May have been topped. Upper canopy is stunted and discolored. 11) Douglas Fir 12.5” DSH, 26’ tall standing at the NW corner of the 16433 house. It is in fair health but bifurcates at the 10’ mark and the codominant stems twine. May have been topped. 12) Big Leaf Maple (Acer macrophyllum) clump standing 15’ north of #11 and on the north fenceline. There are 10 stem in the stand varying from 3-6” DSH and they average 20’ tall. Most likely stump sprouts. 13) White Ash (Fraxinus Americana) 10” DSH, 26’ tall 9’ spread standing 20’ west of the #12 tree and in the fence line area. Fair condition. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 14) Excelsa Cedar (Thuja plicata ‘Excelsa’) 20” DSH, 25’ tall standing 10’ west of #11. Tree is in good condition. 15) Redwood (Sequoia sempervirens) 26” and 24” DSH, 50’ tall standing 17 west of #14 and 8’north of the fence. Separates at base. Good condition. 16) White Ash 5.5” and 8.5” DSH, 37’ tall, 16’ one sided spread standing 10’ SSW of #15. Fair condition. Tree separates at 3’ level. 17) Redwood 28” DSH, 48’ tall standing 20’ west of the #15 tree and 8’ north of the fence. Good condition. 18) White Ash 5” and 10” DSH, 39’ tall, 10’ spread standing 15’ SW of #15. Fair condition. Tree separates at 40” level. 19) Redwood 27” DSH, 46’ tall standing 20’ west of the #17 tree and 8’ north of the fence. Good condition. 20) White Ash 13” DSH, 26’ tall, 8’ spread standing 22’ W of #18. Fair condition. Tree bifurcates at 5’ mark. 21) White Ash 6.5” and 10.5” DSH, 25’ tall, 8’ spread standing 21’ east of the NW corner of the property. Fair condition. Tree separates at 13” level. 22) Weeping Willow 17.5” DSH, 20’ tall, standing 17’ south of the north line and 14’ east of the west line. The tree leans east near 20 degrees and extends 24’ and about 14’ wide. 23) Cottonwood (Populus trichocarpa) 25” DSH, 65’ tall, 18’ spread standing 6’ west of the west fence line and 20’ south of the north line. Tree has a significant structural fault near the 30’ level. Decay may be present. 24) Red Alder (Alnus rubra) 13” and 15” DSH, 45’ tall, 8’ spreads standing 5’ west of the west line and 15’ south of #23. Both stems have less than 15% viable canopies and both lean lightly to the southeast. 25) Western Red Cedar (Thuja plicata) 13.5” DSH, 35’ tall standing 5’ east of the west line and 8’ south of the #24 tree. There is a tree fort fastened between this tree and the #26 tree which has been in place at least 8 years based on how much the tree has grown around the boards and bolts. Tree is in poor condition with little to no new growth and weak color. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 26) Western Red Cedar 11.5” DSH and 14” DSH, 35’ tall standing 10’ south of #25 and holding the other end of the fort. Stems separate from the base. Tree is in poor condition. 27) Western Red Cedar 12” and 14” DSH, 31’ tall standing 9’ south of #26. The stems separate from the base and the larger is on the east side. Tree is in weak condition. 28) Western Red Cedar 15” DSH, 30’ tall standing 42’ north of the SE corner of the 16433 property and 6’ east of the west line. It is in weak condition. 29) Western Red Cedar 18” DSH, 26’ tall standing 6’ south of the #28 tree. It is in weak condition. 30) Cottonwood 16” DSH, 52’ tall, 16’ spread standing 5’ west of the four way corner at the NW corner of the 16451 parcel and in the property due west of it. Tree is in fair condition. 31) Cottonwood tree 12” DSH, 65’ tall, 9’ spread standing as part of a clump 15’ south and 15’ east of the NW corner of the 16451 property. It is in fair condition. 32) Cottonwood tree 12.5” DSH, 42’ tall, 9’ spread standing just south of the #31 tree. It is in fair condition. 33) Cottonwood tree 22.5” DSH, 75’ tall, 18’ spread standing in between and just west of the #31 and #32 trees. It is in fair condition. There are two subordinate saplings, 4” and 6” caliper, standing below this tree and closer to the west fence. 34) Cottonwood tree 10” DSH, 35’ tall and 14” DSH, 45’ tall, 9’ overall spread standing 28’ south of the #31-33 clump. It is in the west fence line and in weak condition. 35) Cottonwood tree 13” DSH, 32’ tall, 8’ spread standing 35’ south of the #34 tree and against the fence. It is in fair condition. 36) Big Leaf Maple 10” DSH, 33’ tall, 10’ spread standing 5’ north of the SW corner of the 16451 property. It is in fair condition. 37) Grove of at least twelve cottonwood saplings, all less than 6” DSH, standing at about the center point of the south side of the property and on the southern neighbor’s side of the line. Fair conditions. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 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: There are two levels of concern at this site, primary and secondary. The primary construction impact zone includes the environs immediately within the boundaries of the new home base areas (see Figures 4 and 5), those in the area of the new road improvements, the areas expected for the driveway access to each home site, and the regions within ten feet of those boundaries. Trees #1-11, #28, and #31-33 clearly stand in the primary impact zones. They will be removed at the time of clearing and grading The secondary impact area includes the trees which have root systems extending within the construction area. This region, the Critical Root Zone (CRZ), is defined as a circle with a radius of one foot per inch of tree diameter. For example the #13 White Ash, with a 10” DSH, has a 10’ radial CRZ. Typically intrusion within the CRZ is strongly discouraged by the tree care industry. However trenching type incursion, that is excavation that will occur 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 again related to the diameter inches of the tree in question but not quite in a direct proportion as in the CRZ. Figure 6 below illustrates the relationship. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 6. 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. In the case of the #10 White Ash mentioned above, the #2 house base area will be 20’ back from the north property line so will not interfere with tree. But if other grading is required along the edges of the parcel then the #10 tree, as seen in Figure 6, has a 5’ Structural Root Plate, and excavating will have to stay outside of that area. Looking at the entire row of trees along the north fence line the redwoods have the largest diameters and will require the full 10’ set back. They are already 8’ north of the line so only 2’ of their SRP extends into the parcel. The Ash standing on the property line have diameters which indicate no greater than 6’ SRPs. The #22 willow has a 17.5” DSH and means it has somewhere around an 8’ SRP. The area shown on the short plat as set aside for the #5 house will be just at 8’ from the base of the tree. The largest of the cedars standing on the west end of the 16433 parcel has an 18” DSH which indicates an 8’ SRP. The cottonwoods and maple standing on the west end of the 16451 parcel range between 10” DSH and 13” DSH which indicate SRPs between 6’ and 7’ radial spread. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner The chart shown in Figure 7 below is used to determine what percentage of a tree’s Critical Root Zone will be affected by trenching type incursion. In general trees can sustain losses of up to 30% of the overall area within their CRZ without having long term detrimental results. Figure 7. Chart giving the loss in critical root area as a function of the radial distance to the CRZ disturbance. For the trees along the north border, the CRZs of the redwoods (26-28’ radial spread) overlap those of the ash (10-12’ radial spreads) in the fence line. From the chart in Figure 7 the redwoods require a 19’ setback to prevent detrimental impact. As they are 8’ north of the fence line an 11’ non-intrusion zone along the length of the north line should be adequate for all the trees. The #22 willow requires a 13’ set back which appears to overlap with the graded area at the NW corner of the #5 home site. The cedars #25-27 are in an region set aside as a sensitive area. But there appears to be step down grading which will occur in their vicinity. Their CRZ should not be disturbed within 10’ of the base of the trees. If fill is being brought in it can be no deeper than 4” within 10’ of the trees. The #29 cedar is close to the SW corner of the graded site for the #5 home. It requires a 13’ set back. The cottonwoods and maple on the west end of 16451 all have 10’ maximum setbacks. They also appear to be in regions of stepped down grading. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Recommendations: Nearly all the trees present on site in this case will have to be removed. The majority stand in the primary impact zone for the development. Of these only the #2-4 Scots pines are in at least average condition. The others are dead, in weak to poor condition, and/or have structural issues making them undesirable to retain. Removal and replacement with young, healthy trees is the most viable option for these spaces. The #22 willow and # 29 cedar stand in the center of grade transition zones. Neither is in good condition and both require CRZ protection at 18’ out from their bases. If it is not possible, or practical, to maintain these protection circles then the trees should be removed. Note that burying the CRZs of trees with more than 4” of soil interferes with their biological functions and for all intents and purposes is no different from cutting the roots. Raising grade within the CRZ of a retained tree is not allowed. Typically protection fencing such as 6’ chain link is set at the CRZ limits for retained trees. For the north side border stand the simplest thing is to just run the fence 11’ south of the property line for the length of the row. If the #22 willow is to be kept than it will require a circular enclosure at 17.5’ radial distance. Obviously the tree itself will extend beyond the fence line and may require clearance pruning. The protection fence for the #25-27 cedars can be set at their 10’ one-sided encroachment limit on the east and then tapered around both ends at 14’ distance. The #29 cedar, if it is to be kept, will have to be circled at 18’ radial distance. The two cottonwoods and maple at the west end of 16451 should be fenced at their CRZ extent and the fence tied back to the existing wood one. All the retained trees should be covered with 6-8” of arbormulch within the region of their CRZs. Excelsior cedars, Deodar cedar, Alaska Weeping Cedar, and even Sequoia are great options for evergreen replacements. Columnar maples, hornbeams, beech, Katsura, Crimson King maple, and certain oak varieties are options for larger deciduous. Japanese Snowbell, Stewartia, redbuds, vine maples, and columnar magnolias can work for color and more mid-sized options. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner 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 D.R. Strong Consulting Engineers 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 Certified Arborist Qualified Tree Risk Assessor ISA #PN-5847A ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 1. Aerial overview of the two property. The subject trees are labeled in red. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 2. Close up aerial view of the 16433 property. Not that the faint red lines designating the boundaries appear to be shifted to the south. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 3. Close up aerial view of the 16451 property. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 4. Excerpt from plot plan showing location of proposed new lots and road improvements for the 16433 parcel. Note the step down grading notation at the west (left) side of the image. ______________________________________________________________________________ ______ PO Box 1261, Mercer Island, WA 98040 • 206-275-0991 • paulscottsinclair@gmail.com Scott Sinclair - Owner Figure 5. Excerpt from plot plan showing location of proposed new lots and road improvements for the 16451 parcel. Note the stepped grading at the west end of the property.