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Home My WebLink AboutRenton Marriot Arborist Report Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 1 | P a g e Puget Sound Energy Renton Marriott Project 1200 Lake Washington Blvd, Renton WA Level 1 Tree Risk Assessment Prepared for: Val Buzunov, PSE Project Manager Prepared by: Dan Olsen, Asplundh Tree Expert, LLC Consulting Utility Forester ISA Board Certified Master Arborist MN-4070BU Date: 1/5/2018 Background Puget Sound Energy (PSE) is proposing the removal of a group of five trees located near a recently re-located 115 kV transmission line at 1200 Lake Washington Blvd. The trees are located within a steep slope area and are subject to the City of Renton’s Critical Areas regulations. An arborist report is required to permit tree removals. I inspected the site on Tuesday, December 26, 2017 and performed a Level 1 Visual Tree Risk Assessment. The following information represents my findings and recommendations. Scope of Assignment I was asked to inspect the site and provide a written report that will be submitted to the City of Renton for permitting purposes. A Level 1 Limited Visual Assessment was performed by viewing the south and east sides of the trees from the access road. The diameter at breast height (DBH) was visually estimated and the heights were measured with a laser range finder. Site and Tree Observations The location is an active construction site. Clearing and grading activities have recently been performed around the subject trees. The trees are surrounded by PSE’s facilities including: a re-located 115 kV transmission line on the north side of the trees, existing three-phase distribution lines located to the south, and a metal tower supporting a de-energized transmission line located to the east (see Image 1 Site Map). The five subject trees consisted of a cluster of four black cottonwoods (Populus trichocarpa) and one big leaf maple (Acer macrophyllum) (Image 2). Three brush-sized (or less than 6-inch DBH) cottonwood trees were also present within the group (Image 4). The cottonwoods were 15 to 17” DBH and 80 to 105’ tall (see Table 1 Tree Observations). The big leaf maple was 50’ tall and was a multi-stemmed tree consisting of five main stems measuring 5 to 7” DBH. All of the stems originated as cut stump sprouts (Image 3). Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 2 | P a g e The group of trees stood approximately 25’ from the recently re-located 115kV transmission line. Trimming had recently occurred to provide clearance from the new overhead wire location. Three of the cottonwoods were over-trimmed with all the lower branches being removed leaving only the upper crowns. The fourth cottonwood and the maple required minimal trimming. The health and growth of the trees appeared normal for the species. The main concerns with the cottonwoods are poor trunk taper and low live crown ratios (See Figures 1 and 2). These conditions increase the risk of failure when loads are placed on the upper crown due to trunk slenderness. The main concern with the big leaf maple is the main stems have possible weak attachments at the root crown. This is a predictable point of failure as the stems increase in height and diameter. Table 1 Tree Observations Discussion and Recommendations Large, fast-growing species such as cottonwood and big leaf maple are incompatible with overhead power lines as these trees often cause power outages. Many documented outages can be attributed to cottonwood limb breakages falling into the lines. Additionally, big leaf maples have been classified by utilities as ‘cycle-busters’ because this fast-growing species commonly re-grows into the lines between regular maintenance tree trimming cycles. Therefore, these incompatible trees should be removed and replaced with a compatible species whenever it is feasible. Both cottonwood and big leaf maple have a poor tolerance to construction activities and the recent clearing and grading will likely have negative impacts on this group of trees. Trees affected by grade changes within their dripline often decline and die within five to eight years after construction. The subject trees are not presently an imminent threat and will not likely fail during normal weather conditions. However, the observed structural defects, such as poor taper, low live crown ratio, and weak stem attachments, increase the likelihood of failure during storm events. Due to these trees being located near high voltage transmission and distribution lines with the potential to cause power outages affecting thousands of customers, I recommend removal of the four cottonwoods, the big leaf maple, and the cottonwood brush, and replacing with a power line compatible species. Tree #Species Height DBH Health Condition LCR Taper* 1 Cottonwood 95'15"Good 47' remaining crown 50%76 2 Big leaf maple 50'~19"Good Multi-stemmed from stump sprouts N/A N/A 3 Cottonwood 100'15"Good 20' remaining crown - very low LCR and poor taper 20%80 4 Cottonwood 104'17"Good 20' remaining crown 19%74 5 Cottonwood 80'16"Good Full Crown but poor taper 70%60 *Taper greater than or equal to 50 is a hazard (See Figure 1) Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 3 | P a g e Image 1. Site Map Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 4 | P a g e Image 2. View of the trees from the east Tree #3 Tree #1 Tree #4 Tree # 2 Tree #5 Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 5 | P a g e Image 3. Big Leaf Maple Stump Spouts Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 6 | P a g e Image 4. View of the trees from the southwest Tree #5 Cottonwood brush Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 7 | P a g e Figure 1. C. Mattheck, 2015. The Body Language of Trees Trunk Taper important for even distribution of mechanical stress Calculate by dividing tree height by the trunk diameter. The same units of measurement are used. T = Height(ft.)/Diameter(ft.) Taper is related to LCR C. Mattheck Asplundh Tree Expert LLC Region 072 & 172 20004 144th Avenue NE Woodinville, WA 98072 8 | P a g e Figure 2. Dunster, J 2009. Tree Risk Assessment in Urban Areas and the Urban/Rural Interface Live crown ratio is the proportion of the height of the tree that is green An LCR below 30% is the point at which the extent of the foliage is insufficient to complete provide enough carbohydrate to complete annual ring over the entire tree. Trees with LCR below 30% are more likely to snap off. Dunster, J., 2009