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HomeMy WebLinkAboutTR_Arborist_Report_180917_v1 August 10, 2018 Federal Air Marshalls Building; 500 Powell Ave SW Prepared by: Sean Joey Murphy, Certified Arborist (PN-8136A) Hazard Tree evaluation: Black Cottonwood (Populus trichocarpa) Tree characteristics: *PLEASE NOTE* In a typical arborist report, the trees may be identified individually and have a separate report written for each. In this case the trees are treated as a collective as they are assumed to be growing in the same cluster, and because the accessibility to each tree is restricted. Any applicable and unique characteristics to a specific tree will be noted. *Recommendation for trees begin at the end of page 2* The 10 trees being looked at are a group of 8 Black Cottonwood trees to the east of the property, and branches overhanging the south end of the property. There are also 2-3 trees on the south and southeast ends of the property that will be mentioned that are not an immediate threat. The trees on the east end of the property range in DBA (diameter at breast height) of approximately 22” to 46”. The height range of the trees from approximately 80’ to 135’ indicating mature to over-mature in their life cycle. The trees range from having minor to major asymmetry. One tree has a co-dominant crown, another is possibly co-dominant (underground), the rest are dominant crown class. All are likely inter- connected underground as is typical with the species. There is no apparent special value to the trees and they grow wild and are indigenous. Important to note is that the black cottonwood is a tree that will almost pose a hazardous situation and is unsuitable in cases that it is closely bordering an area that would have any kind of possible damage present. The tree grows very fast, is susceptible to breaking branches, broken tops, total failure, pests and disease. They also are one of the most destructive trees to pavement due to the vigorous nature of their growth. Tree Health: The tree health, besides most the trees being mature to over-mature, is generally normal. The color, density, density is mostly normal. The annual shoot growth and woundwood development is generally normal and the trees that are not overly mature have vigorous growth. The trees compete heavily with undergrowth and adjacent pavement. Site Conditions: This is a green belt/wetlands area that requires special attention that may typically avoid tree removal except for special circumstances where the protection of property and life is to be considered. The irrigation for this property is adequate to excessive. This is to be expected as this species of tree typically thrives in marshy locations. I would estimate by root damage already done and by the typical drip line of this species that approximately 5-10% of the root area is paved. The prevailing wind in this area is typically from the S and SE and this cluster of trees is not protected from wind throw given their height. Snow storms in this area occur seldomly. Target: The target rating portion for this report will be 4/4 (highest). In the strike zone of the trees are heavy pedestrian traffic, auto parking, various small features, a parking structure, a large generator, fences, and a building. Unique to this property is the security issues that could arise due to failure. This is a federal law enforcement agency with high security measures. In the event of another failure similar to the first the fence would be knocked down and would allow unauthorized entry. Tree Defects: The trees have moderate exposed roots in approximately 10% of the roots observed. The lean of the trees range from 0 tp 25 degrees. In the various trees there are codominant forks, broken or dead branches, a few hangers, excessive end weight, sever lean, and included bark. Besides the various issues, the trees are in moderately good health. But as stated before, the health of the trees isn’t the issue as much as the inherit problems that come with this species. In other words, a perfectly healthy black cottonwood approaching maturity will always pose the risk or partial to complete failure, along with destructive roots. Recommendation: I strongly recommend and advise the complete removal of the 8 black cottonwood trees I have observed. Further, as the winds typically pick up in this area at the beginning of the fall, it would mitigate risk to do this in an expedited manner. I would also recommend that the largest of the branches extending towards the building on the south side of the property should be removed. The hazard rating I have assigned for these trees as a collective are 11/12. This rating comes from an aggregate of three different criteria, with the highest indicating the highest risk of hazard: Failure potential: 3 of 4- Depending on interpretation this could also be 4/4, which would indicate ‘severe’. I rated this slightly lower because while a cottonwood does always pose a high risk of failure of branches and large parts, I did not observe any imminent (within the next day or two) threats. Size of part: 4 of 4- These trees are at risk of partial to total failure. Target rating: 4 of 4- due to the constant use of the area of human life and very expensive to replace permanent structures. Perhaps the most important factor to consider is that these trees are reported to have failed previously by staff. All of these trees are close enough to the targets to pose a significant risk to property, life, and security. Besides the 8 trees that should be removed that are the subject of this report, I would recommend that two of the trees on the southeast corner of the property and the tree that the branch is being removed from on the south side of the property should be considered for removal. These pose less of a risk as they are still young in their life cycles, but they are still large enough and are leaning enough that they will increase in risk as time goes on. Overall, it is generally a good idea to identify any black cottonwoods that are close enough to a target to pose a risk when they are at full growth and remove them due to their fast growth and unpredictable health. Please feel free to contact me with any additional questions or to discuss Sean Murphy PN-8136A 253-347-5230 Page 1: Table of contents Page 2: Cluster of trees in relation to target Page 3: Example of lean of tree in relation to target Page 4: Branch strongly recommended for removal leaning over south side of property Page 5: View of cluster from the taken from the north in relation to targets Page 6: Example of large split very susceptible to failure Page 7: Example of codominant splits, dead branches, and included wood susceptible to failure Page 8: Shot of largest tree growing into fence with plane of lean heading towards targets Page 9: Largest tree growing into fence Page 10: Epicormic growth Page 11: Large codominant split more likely to fail Page 12: View of cluster from ground Page 13: Large split and multiple trees with big leans Page 14: Tree with largest lean threatening parking structure Page 15: Large split up top with high probability of failure Page 16: Trees on south side of property that should also be considered for removal while at a younger stage but don’t impose as immediate a risk as the original 8. Page 17: Trees on southeast side of property that should also be considered for removal while at a younger stage but don’t impose as immediate a risk as the original 8.