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Tree assessment Hort Science, Inc Bonde Ranch City of Pleasanton Page 5 Tree Risk Tree risk evaluation is the systematic process of assessing the potential for a tree or one of its parts to fail and, in so doing, injure people or damage property All trees have the potential to fail The degree of risk will vary with the size of the tree, type and location of the defect, tree species, and the nature of the target All trees were assessed using the procedure outlined in A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas(N Matheny & J Clark 1994 (2nd edition International Society of Arboriculture Champaign IL) This method ranks the relative risk of trees within a given site Following a visual inspection of tree health and structural condition, the part of the tree most likely fail within the next 3 years was identified (e g branch, stem, or whole tree) as was the target that would be impacted The relative risk associated with each of the 65 trees was evaluated using the following components Failure potential (4 points) - identifies the most likely failure and rates the likelihood that the structural defect(s)will result in failure within the next 3 years The part of the tree most likely to fail was assessed using the following scale 1 - low-defects are minor (e g dieback of twigs, small wounds with good woundwood development) 2 -medium -defects are present and obvious (e g lean or bow that has developed over time, cavity encompassing 10-25% of the circumference of the stem, codominant stems without included bark) 3-high -compounding and/or significant defects present (e g severe lean, cavity encompassing 30-50% of the circumference of the stem, multiple pruning wounds with decay along a branch) 4 -severe-defects are very severe(e g partial uprooting of leaning tree, decay conks along the main stem, cavity encompassing more than 50% of the stem) Size of defect(4 points) - rates the size of the part most likely to fail Larger parts present a greater potential for damage Therefore, the size of the failure affects the potential for injury or damage The scoring system was as follows 1 -most likely failure less than 6" in diameter 2 -most likely failure 6 - 18" in diameter 3 -most likely failure 18 -30" in diameter 4 -most likely failure greater than 30" in diameter Target rating (4 points) - rates the use and occupancy of the area that would be struck by the defective part For the project areas, the following scoring was employed 1 -occasional use (e g lawn or open space) 2 - intermittent use (e g sidewalk, back yards) 3-frequent use (e g street parking) 4-constant use(e g residence)