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November 18, 2010

Have a campus project? Look out for trees

  • Some are worth tens of thousands of dollars, so UW aims to keep them out of harm's way.
    Tree Solutions


    The University of Washington values the benefits provided by the trees and vegetation throughout the campus.

    Every year people visit the campus to view the flowering cherry trees that line the quad and Rainier Vista. Many trees are named after significant contributors to the development of the university or in memory of those that have died.

    The university understands how the trees are in many cases a significant resource that brings high value to the campus.

    Assessing trees

    One of the first requirements of a capital improvement project on the University of Washington’s Seattle campus is to inventory, assess and protect existing trees that may be negatively impacted by new construction.

    Image courtesy of Tree Solutions [enlarge]
    Several measures were taken to protect this 90-foot-tall American elm tree, considered one Seattle's finest, during a recent campus project. The tree was fenced off, the trunk was wrapped with mattresses and a container truck was positioned to block falling debris.

    For jobs costing over $10 million, the Capital Projects Office hires an independent arborist to assess the trees around the development site. For smaller projects, the campus arborist performs the assessment.

    Trees are evaluated for baseline information such as species composition, diameter, size, vigor and structural condition. Other specialized information that gets collected and evaluated includes risk of failure, significance of the tr ee and its appraised monetary value.

    Prior to inspection, the arborist will receive a site map showing the existing infrastructure and the location of each tree. The university uses GPS- and GIS-based tree inventories to quantify some aspects of its urban forest. To date, 9,500 of an estimated 11,000 trees have been numbered, tagged with an aluminum marker and measured for diameter.

    Once the baseline information is obtained and the tree is evaluated for risk, the arborist evaluates the significance of the trees in the project. The evaluation designates a tree as “extraordinary,” “exemplary,” “significant” or “non-significant” based on criteria such as rarity of species, specimen quality, aesthetic contribution and cultural/educational significance. If a tree meets a threshold for one of these criteria, certain protection measures are applied during construction.

    Protecting the trees affected by campus projects is a high priority, and the university uses appropriate measures to protect their root systems, trunks and canopies.

    Measures include chain link fence enclosures, tree protection signage, temporary irrigation and mulch, tying back limbs that may be contacted by equipment, hand trenching in the critical root zone to limit root loss, and monitoring by a qualified arborist whenever work is occurring in the protected area of the tree. Additional site-specific requirements may also be incorporated into the planning and design of the project.

    An ‘extraordinary’ tree

    In a recent project the university was looking to redevelop a site to provide additional student housing.

    UW tree inventory

    The university’s Grounds Department is compiling a tree inventory. Details are available online at depts.washington.edu/czone.

    Click on “2009-2010 Campus Tree Care Plan.” Program goals include:

    Inventory: The inventory allows the university to more efficiently maintain, monitor and renew the campus urban forest. In addition to assisting the development of a tree management plan, the inventory will be used as an educational tool for researchers and students in many disciplines. Once complete, the inventory information will be posted on the Grounds Department website, along with an interactive map.

    Management plan: Using the tree inventory, a tree management plan can be developed for restoration of the tree canopy. The inventory will be analyzed for age/longevity of the canopy, species diversity and educational value, and will identify recommended species and locations where new plantings can be installed.

    The university identified a single American elm tree that needed to be evaluated. The tree was 90 feet tall, had a 48-inch diameter and a canopy spread of 85 feet across. It was in good condition and structurally stable.

    It was also discovered that the tree was referenced in Arthur Lee Jacobsen’s 2006 book “Trees of Seattle” as one of “the city’s finest specimens of American elm.” Based on the arborist evaluation, the tree was found to meet the university’s definition of extraordinary significance.

    Although preserving the tree required a major change in the pre-design layout of the housing units at a significant additional cost to the university, the tree was considered to be worth the time, money and effort to preserve. The new design for the site incorporates the tree as a major focal element of the landscape. The tree will now receive special consideration for protection during the next several phases of development.

    During the demolition and abatement phase, the tree was surrounded by protective fencing, but the contractor was concerned the fence might not be sufficient to stop bricks from falling off the adjacent four-story structure and damaging the tree. One solution was to park a container truck between the building and the tree to take the impact. The base of the tree’s trunk was also wrapped with mattresses as an added buffer from falling debris.

    So what would happen if a protected tree was damaged during construction?

    With information collected in the inventory, an estimated tree value can be determined using current industry standard methods. These methods consider the size of the tree, species, condition, site characteristics and location so that a credible value can be obtained. This value can then be used to determine the cost to replace the tree if it dies or assign a value to the amount of damage created by a contractor or outside source.

    The extraordinary American elm discussed above was valued at well over $30,000.

    Sean Dugan is the senior consulting arborist with Tree Solutions in Seattle. Information in the article was adapted from the University of Washington’s Campus Tree Care Plan.

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