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HomeMy WebLinkAboutRS_TRA - Summit Park (Renton)Tree Risk Assessment Report Renton Condominium Association Prepared For: Bell-Anderson & Associates ℅ Jennifer Corp General Manager Kent, WA 98064 253.852.8195 ext. 205 jcorop@bell-anderson.net Prepared By: Davey Resource Group Inc. 18809 10th Ave NE Shoreline, WA, 98155 Contact: Todd Beals todd.beals@davey.com Local Office: 253.656.1650 Corporate Office: 800.966.2021 Notice of Disclaimer Assessment data provided by Davey Resource Group is based on visual recording at the time of inspection.Visual records do not include testing or analysis and do not include aerial or subterranean inspection unless indicated. Davey Resource Group is not responsible for discovery or identification of hidden or otherwise non-observable risks. Records may not remain accurate after inspection due to variable deterioration of surveyed material. Risk ratings are based on observable defects and mitigation recommendations do not reduce potential liability to the owner. Davey Resource Group provides no warranty with respect to the fitness of the trees for any use or purpose whatsoever. Table of Contents Introduction 3 Methods 3 Limits of the Assignment 4 Risk Assessment Methodology 5 Tree Risk Assessments 7 Tree #3695 - Red Alder (Alnus rubra)7 Risk Categorization 7 Mitigation Options 7 Tree #3696 - Red Alder (Alnus rubra)8 Risk Categorization 8 Mitigation Options 8 Tree #3697 - Red Alder (Alnus rubra)9 Risk Categorization 9 Mitigation Options 9 Tree #3698 - Red Alder (Alnus rubra)10 Risk Categorization 10 Mitigation Options 10 Tree #3699 - Bigleaf Maple (Acer macrophyllum)11 Risk Categorization 11 Mitigation Options 11 Tree #3700 - Bigleaf Maple (Acer macrophyllum)12 Risk Categorization 12 Mitigation Options 12 Tree #3701 - Bigleaf Maple (Acer macrophyllum)13 Risk Categorization 13 Mitigation Options 13 Tree #3702 - Bigleaf Maple (Acer macrophyllum)14 Risk Categorization 14 Mitigation Options 14 Concluding Remarks 15 Appendix A: Maps 16 Appendix B: Risk Rating & Likelihood 17 Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 2 of 17 Introduction Davey Resource Group Inc. (DRG) was contracted to perform a Level 2 Tree Risk Assessment on eight (8) trees to the east of South 51st Court in Renton Washington. The trees were growing on the western edge of a Native Growth Protection Area (NGPA),Parcel Identification Number 808335TRCT. On April 1, 2021 an International Society of Arboriculture (ISA) Certified Arborist (NE-6913A) and Qualified Tree Risk Assessor from DRG conducted an assessment of the trees. The trees were assessed by their location, size, current condition, and overall health. The data was then used to determine a risk rating. The current edition of the Tree Risk Assessment Manual (ISA, 2013) was used to guide the risk rating of the trees as well as the potential strategies for care and risk abatement. There are many factors that can limit specific and accurate data when performing evaluations of trees, their conditions, and values. The determinations and recommendations presented here are based on current data and conditions that existed at the time of the evaluation and cannot be a predictor of the ultimate outcomes for the trees. The purpose of this report is to provide the details of the risk assessment of the tree, including an assessment of the current condition, health, and recommendations for maintenance. The findings in this report can be used to make decisions on whether the trees may need to be removed, or can be retained with restorative pruning and plant health care. Methods Data was collected by an ISA Certified Arborist (Todd Beals - NE-6913A) on April 1, 2021. A visual inspection was used to develop the findings, conclusions,and recommendations found in this report. No physical inspection of the upper canopy, root crown excavation, resistograph or other technologies were used in the evaluation of the trees. The following attributes were collected for each site: Condition:Condition ratings were based on but not limited to:(1) the condition and environment of the tree’s root crown; (2) the condition of the trunk,including decay, injury, callusing or presence of fungus sporophore; (3) the condition of the limbs, including strength of crotches, amount of dead wood, hollow areas, and whether there was excessive weight borne by them; (4) the condition and growth rate history of the twigs, including pest damage and diseases;(5) the leaf appearance, including abnormal size and density as well as pest and disease damage. Using an average of the above factors together with the arborist’s best judgment, the general condition of each tree was recorded in one of the following categories adapted from the rating system established by the International Society of Arboriculture: ●Good:A fully branched and leafed canopy; branches over 2 inches in diameter exhibit little to no dieback; little to no epicormic growth (i.e., sprouting from the trunk, limbs, or roots); and little to no aesthetic damage from insects or disease. The tree displays a growth habit characteristic of the species. The wood has no major structural problems and no significant mechanical damage. The tree exhibits good overall vigor. ●Fair:The canopy is thinning and there is less than average new growth present; or there is noticeable dead wood over 2” diameter or dieback throughout the majority of the crown; or there Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 3 of 17 is significant mechanical damage to the trunk or root system; or the tree is otherwise exhibiting significant signs of stress and potential decline.The following signs or symptoms may be present in the tree: significant damage from non-fatal or disfiguring diseases, minor crown imbalance or thin crown, and/or stunted growth compared to adjacent trees. This condition also includes trees that have been topped but show reasonable vitality and no obvious signs of decay. ●Poor: The tree is in obvious decline or poses significant risk which requires immediate mitigation. There are significant amounts of dieback or dead/dying limbs greater than 2” diameter; there is minimal to no growth; or there is extensive decay to the trunk or root system, raising concerns of structural integrity. A tree in this category may also have severe mechanical damage or poor vigor threatening its ability to thrive. ●Critical: The tree is dying and/or presents an unacceptable risk which necessitates immediate removal. ●Dead Tree Number:Tree ID number was assigned and a numbered aluminum tag affixed to the tree. Stems:The number of stems was recorded. Location and Unique ID: An X and Y coordinate was generated for each tree site. Species: Trees were identified by genus and species,cultivar if evident, and by common name. Diameter at Breast Height (DBH): Trunk diameter was recorded to the nearest inch at 4.5 feet (standard height) above grade except where noted. When limbs or deformities occurred at standard height, measurement was taken below 4.5 ft. The DBH of multi-trunk trees was recorded for each stem Height:Tree Height estimated to the nearest <5ft. Avg. Canopy Radius:Average dripline distance was measured. Limits of the Assignment There are many factors that can limit specific and accurate data when performing evaluations of trees, their conditions, and values. The determinations and recommendations presented here are based on current data and conditions that existed at the time of the evaluation and cannot be a predictor of the ultimate outcomes for the trees. A visual inspection was used to develop the findings, conclusions, and recommendations found in this report. Values were assigned to grade the attributes of the trees, including structure and canopy health, and to obtain an overall condition rating. No physical inspection of the upper canopy, root crown excavation, and resistograph or other technologies were used in the evaluation of the trees. Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 4 of 17 Risk Assessment Methodology This evaluation follows the tree risk assessment methods developed by the International Society of Arboriculture (ISA). It consists of an inspection of the visible tree parts including surface roots,trunk, scaffold limbs, and canopy. The hazard and risk assessment results in a risk rating for the tree to help quantify the level of risk accepted by the tree’s owner. To summarize the information about the trees that received a hazard evaluation, an overall hazard rating is obtained by assessing and assigning a value to the failure potential, identifying the size of the tree part most likely to fail (e.g., branch, one stem, or whole tree) and determining site use around the affected tree. Each of these three characteristics is assessed as follows: Condition of Concern – Describes the part most likely to fail. The larger the tree part, the greater the potential for damage; therefore, the size of the failure part affects the overall hazard potential, and is described according to: ●Part Size - Typically the diameter of the limb or tree part ●Fall Distance - The distance of the part from the ground ●Target - The presence of any target(s) that could be impacted by failure Likelihood of Failure – Identifies the most likely point of failure and rates the likelihood that the observed defect(s) will result in part failure within the next 3 years.Failure potential is rated as: ●Improbable (defects are minor and unlikely to result in failure) ●Possible (defects are present and of concern) ●Probable (compounding and/or significant defects present) ●Imminent (defects are serious and imminent failure is likely) Likelihood of Impact – Identifies the most likely point of failure and rates the likelihood that the structural defect(s) will impact the potential targets. Likelihood of impact is rated as: ●Very Low (Occasional use, as in a forest landscape) ●Low (e.g., tree lawn, sidewalk, park path) ●Medium (buildings or people within striking range more than 50% of the time) ●High (Constant and frequent use of the area within striking distance) Consequences of Failure – Rates the level of damage caused by the defective part in the event of failure. The consequences of failure are rated as: ●Negligible (typically small branches <1” diameter,unlikely to cause damage) ●Minor (branches 1-2” diameter, may cause damage) ●Significant (damage would occur) ●Severe (failure would result in major damage) Overall Risk Rating - The values assigned to condition,likelihood and consequences are summarized into an overall risk rating of Low to Extreme for each tree: ●Low (risk is present, mitigation measures may not be required) ●Moderate (mitigation advised within normal maintenance cycle) ●High (mitigation advised within the year) ●Extreme (mitigation necessary as soon as practical) Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 5 of 17 In addition to a risk rating, the trees were also prescribed maintenance recommendations based on general tree health and visual observations. A high-risk rating alone does not necessarily result in a removal recommendation. Conversely, trees with a lower rating may be prescribed for removal based on other factors such as location and species compatibility and/or the severity of specific defects. Whenever recommended tree maintenance would mitigate risk,the residual risk was also noted. A visual inspection and mallet soundings from groundline to 8 feet on the trunk were the primary methods used to develop the findings, conclusions, and recommendations found in this report. Data collection included measuring the diameter of the tree at 4.5 feet above grade, height estimation, canopy radius estimation, a visual assessment of tree condition,structure and health, and a photographic record.Mallet sounding was used to determine the soundness of accessible roots, trunk and branches. Qualitative value assessments grade the attributes of the tree, including structure and canopy health, and to obtain an overall condition rating. No physical inspection of the upper canopy, root crown excavation, and resistograph or other technologies were used in the evaluation of the tree. Example Illustration: Tree defects and conditions affecting the likelihood of failure were assessed around the Root Collar, the Trunk and the Crown Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 6 of 17 Tree Risk Assessments Tree #3695 - Red Alder (Alnus rubra) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 12 60 10 Dead Crown and Branches - Dead Trunk - Located 35ft away and uphill of the nearby home. Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 7 of 17 Tree #3696 - Red Alder (Alnus rubra) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 20 65 15 Fair Crown and Branches - The canopy is one-sided towards the east and the nearby homes. There is minimal growth on the west side of the tree. There was <5% small diameter deadwood throughout the canopy. There was no foliage due to seasonal senescence. Trunk - Located 45ft away and uphill of the nearby home. The trunk was leaning >30 degrees to the east and the nearby home. The is likely due to phototropism and not a structural defect in the trunk. Roots and Root Collar - No visible defects. The soil in the area is seasonally saturated. Risk Categorization The likelihood of stem failure is possible with a high risk of impacting the nearby home. This event is somewhat likely and the consequences of impact are significant. Overall Tree Risk Rating: MODERATE Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: LOW Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 8 of 17 Tree #3697 - Red Alder (Alnus rubra) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 10,11 55 20 Dying Crown and Branches - The canopy of one stem was dead. There was no foliage due to seasonal senescence. Trunk - Located 30ft away and uphill of the nearby home. There were two stems joined near the base where a bark inclusion was present. One stem was dead. Roots and Root Collar - No visible defects. The soil in the area is seasonally saturated. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Removing only the dead stem would likely lead to basal decay in the remaining stem from the large would. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 9 of 17 Tree #3698 - Red Alder (Alnus rubra) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 10,4 60 10 Dead Crown and Branches - Dead Trunk - Located 35ft away and uphill of the nearby home. Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 10 of 17 Tree #3699 - Bigleaf Maple (Acer macrophyllum) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 12 60 10 Dying Crown and Branches - There were 4 large (>4” diameter) dead branches in the upper canopy and similarly sized hanging branches. The east side of the tree is exposed to wind and there were dead branches in the understory trees ~15ft away. Trunk - Located 60ft away and uphill of the nearby home. There were areas of necrotic flaking bark on the lower trunk. Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 11 of 17 Tree #3700 - Bigleaf Maple (Acer macrophyllum) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 9.4 60 25 Dying Crown and Branches - The canopy was mostly dead and there was only one main branch. The east side of the tree is exposed to wind and there were dead branches in the understory trees ~15ft away. Trunk - Located 60ft away and uphill of the nearby home. There were large cracks in each stem Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 12 of 17 Tree #3701 - Bigleaf Maple (Acer macrophyllum) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 10 60 25 Dying Crown and Branches - There were multiple large (>4” diameter) dead branches in the upper canopy and similarly sized hanging branches. The east side of the tree is exposed to wind and there were dead branches in the understory trees ~15ft away. Trunk - Located 60ft away and uphill of the nearby home. There were areas of necrotic flaking bark on the lower trunk. Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 13 of 17 Tree #3702 - Bigleaf Maple (Acer macrophyllum) DBH (in)Height (ft)Avg. Canopy Diameter (ft)Condition 26 90 25 Dying Crown and Branches - Dead branches made up a majority of the canopy. The east side of the tree is exposed to wind and there were dead branches in the understory trees ~15ft away. Trunk - Located 70ft away and uphill of the nearby home. There were areas of necrotic flaking bark on the lower trunk. There were small nesting holes visible along the trunk. The tree split into codominant stems at 15ft above ground level. Roots and Root Collar - No visible defects. Risk Categorization The likelihood of stem failure is imminent with a medium risk of impacting the nearby home. This event is likely and the consequences of impact are significant. Overall Tree Risk Rating: HIGH Mitigation Options Tree removal is recommended or topping at a safe height to leave as a habitat snag. Residual Risk: NONE Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 14 of 17 Concluding Remarks The trees were growing in a seasonally saturated area uphill from the homes. All of the inspected trees were within striking distance of the homes to the west if whole tree failure was to occur. Weak soil attachment due to seasonal saturation can increase the likelihood of tree failure especially in trees that are leaning or have one-sided canopies, which is a typical characteristic of trees growing on the wildland-urban interface. There were trees in the area that had failed at the root plate. Trees to be removed at the project site may be reduced to a safe height and left as habitat snags for wildlife food, nesting, or shelter. Standing or downed deadwood plays an important role in the landscape. Tree removals at the site present an opportunity for designers to promote and increase wildlife activity and diversity at the site. The arborist performing the removals will be consulted to decide the potential for and height of a habitat snag designation on a tree by tree basis. In some cases, guy wires may be attached to the tree and anchored in the ground to create a safe snag out of a taller tree. All pruned tree parts should remain at the site to biodegrade naturally which can promote beneficial decay organisms Image 1. An example image of habitat snag life stages and wildlife potential. Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 15 of 17 Appendix A: Maps Map 1. Site map showing tree id number. Aerial photos are only used for reference. Map projections can distort tree canopy size and locations. Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 16 of 17 Appendix B: Risk Rating & Likelihood The technique used to define the risk of failure and the likelihood of failure involves a determination within two matrices. These matrices are reproduced here from the International Society of Arboriculture datasheets for Tree Risk Assessment, 2013.Appendix 1 Using the ISA Basic Tree Risk Assessment Form Matrix I. Likelihood Matrix Likelihood Of Failure Likelihood of Impacting Target Very Low Low Medium High Imminent Unlikely Somewhat likely Likely Very likely Probable Unlikely Unlikely Somewhat likely Likely Possible Unlikely Unlikely Unlikely Somewhat likely Improbable Unlikely Unlikely Unlikely Unlikely Matrix II. Risk Rating Matrix Likelihood Of Failure & Impact Consequences of Failure Negligible Minor Significant Severe Very likely Low Moderate High Extreme Likely Low Moderate High High Somewhat likely Low Low Moderate Moderate Unlikely Low Low Low Low Prepared by: DRG Inc.April 2021 Prepared for; Renton Condominium Association Page 17 of 17