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<br /> 6.1 C.1 <br /> Page 2 <br /> PUBLIC WORKS SERVICES DEPARTMENT <br /> M E M 0 RAN D U M <br />Date: February 27, 2006 <br />To: Honorable Mayor and City Council Members <br />Through: Peter Ingram, Public Works Services Director~ <br />From: Gordon Mann, Public Works Superintendent \ V <br />SUBJECT: STREET TREE FAILURE DATA ANALYSIS <br />This report is in response to inquiries about recent failures of street trees that have been <br />root pruned. Public Works Services (PWS) staff has investigated several recent failure <br />incidents and has researched methods to test standing trees to determine if a likelihood of <br />failure can be accurately predicted. The report will cover the following areas: <br /> Brief summary of findings <br /> The history of the sidewalk project <br /> The history of Redwood City tree failures <br /> Conclusion <br />Brief Summarv of Findings <br />Approximately 4,790 trees have been root pruned over the history of the sidewalk repair <br />program. The root pruning work around these trees has been directed by City staff during <br />annual sidewalk replacement project construction. <br />Staff findings are: <br />. Four Ash trees located on Bristol Way, Maddux Drive, Pecan Court, and <br /> Massachusetts Avenue were root pruned. One tree failed in late September <br /> (Bristol). One was determined to be unstable and removed prior to failure in late <br /> December (Maddux). Two failed during a storm December 31st (Pecan and <br /> Massachusetts). The Bristol tree was root pruned during the most recent project. <br /> The Maddux and Massachusetts trees were root pruned approximately two years <br /> ago. The Pecan tree was root pruned approximately five years ago. <br />. All four trees failed as a result of a very high wind or significant outside force (hit by <br /> debris box truck) combined with saturated soil conditions at the root crown. <br />. Approximately 1.4% or 67 of the 4,790 root pruned trees have failed over the course <br /> of the program since 1985. <br />. Some branch and twig dieback occurs in most trees following root pruning. <br />. Supplemental irrigation does have a beneficial affect on an individual tree's <br /> response to and recovery from root pruning. <br />. Significant dieback has occurred in approximately 5% of the trees following root <br /> pruning, resulting in follow-up pruning. If individual trees continue to decline over <br />TreFFallure Data Analuysis <br /> Page 1 of 6 <br /> .'.._-, --.- -~. ~M_ .. .--.,.,.. ..._~,--_.-., .--.,---.-". ...----_..__._-.-.,~----~-----'...'.~--~ _..- <br />