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TR-2012-08b OFFICE OF COMMUNITY DEVELOPMENT � ,. CITY HALL 10300 TORRE AVENUE•CUPERTINO, CA 95014-3255 C U P E RT 1 N 4 (408) 777-3308•FAX(408)777-3333•pianning(a)_cupertino.org February 16,2012 Roy or Yvonne Hampton 21821 Oakview Ln Cupertino,Ca 95014 SUBJECT: (RETROACTIVE) TREE REMOVAL PERMIT ACTION LETTER- Application TR-2012-08: This letter confirms the decision of the Director of Community Development, given on February 16, 2012, approving a retroactive tree removal permit to allow the removal and replacement of a hazardous Coastal Oak tree,located at 21821 Oakview Lane with the following conditions: 1. APPROVED PROTECT This approval is based on the arborist report prepared by Michael Bench (Certified Master Arborist WE-189'�, dated January 18, 2012, consisting of 4 pages and entitled: Evaluation of an Oak Tree, Hampton Residence, 21821 Oakview Lane, Cupertino, California, except as may be amended by conditions in this resolution. 2. TREE REPLACEMENT The Director of Community Development has determined that accommodating additional trees on the property would not be feasible and therefore a tree in-lieu fee would be required. The cost to procure, install, and replace two trees is approximately $700.00, of which the applicant has paid on February 10, 2012,in accordance with the City's Protected Tree Ordinance. 3. NOTICE OF FEES,DEDICATIONS,RESERVATIONS OR OTHER EXACTIONS The Conditions of Project Approval set forth herein may include certain fees, dedication requirements, reservation requirements, and other exactions. Pursuant to Government Code Section 66020(d) (1), these Conditions constitute written notice of a statement of the amount of such fees, and a description of the dedications, reservations, and other exactions. You are hereby further notified that the 90-day approval period in which you may protest these fees, dedications, reservations, and other exactions, pursuant to Government Code Section 66020(a), has begun. If you fail to file a protest within this 90- day period complying with all of the requirements of Section 66020, you will be legally barred from � later challenging such exactions. Staff has made the findings necessary to grant the retroactive tree removal permit in accordance with Section 14.18.120 of the Protected Trees Ordinance. Since ly, George Schroeder Assistant Planner (408) 777-7601 georges@cupertino.org Evaluation of an Oak Tree 21821 Oakview Lane Cupertino, CA Evaluation of an Oak Tree � Hampton Residence A��'��'°°L I /C—:�20/�- 0�' 21821 Oakview Lane �' "� � �� Cupertino, California -�--�-�-� ��'�j� �= . ,-� �. .. .� Assignment I was asked by George Schroeder, Planner, City of Cupertino, asked me to evaluate a coast live oak tree located in the rear yard of the Hampton Residence, 21821 Oakview Lane, Cupertino. Observations My first impression of the condition of the coast live oak tree at the Hampton residence based on the photos and documents, which were included with the assignment, was that the disease of this oak tree was not serious and not life threatening. However, the inspection of this tree reveals a considerably different conclusion. The subject tree is a coast live oak(Quercus agrifolia). It has a trunk diameter of 20.2 inches in diameter at 54 inches above grade. It's overall height is approximately 35 feet tall and has a canopy spread of approximately 30 feet. The canopy is quite dense and the annual branch tip growth is approximately 6-8 inches, which is vigorous. The leaf color is deep dark green. These characteristics typically indicate a healthy specimen. However, the tree's health is not the problem with this tree. The tree is infected with the fungus disease (Phytophthora cactorum). Ordinarily coast live oak trees infected with this disease pose a relatively minor risk to the tree's condition. In the vast majority of the cases, which I have seen, the disease manifests itself in 1 or more infection locations about the size of a silver dollar or slightly larger at sporadic locations on the trunk. In this case, the disease has concentrated in two areas on opposite sides of the trunk. On the west side the disease forms an eleven inch wide area extending down the trunk about 2 feet. On the east side the disease forms a strand about 6 inches wide, also extending about 2 feet down the trunk. In my experience, these concentrations of this disease are very large and quite unusual. This disease typically extends into the interior wood, which is called sapwood decay,to a depth of approximately 3 inches. The vascular flow in these diseased areas is effectively stopped. With the disease on the east and west sides, the vascular flow has been reduced primarily to the north and south sides of the trunk. An important factor is that the diseased wood is highly brittle and easily fractured. The attached drawing shows my estimate of the diseased area. Mr. and Mrs. Hampton reported that the tree had been sprayed to fight the disease, but that they observed no effect or decline of the disease. This is not surprising, because fungicides or other pesticides are not known to be effective for fighting this disease in most cases. Prepared by Michael L. Bench, Consulting Arborist January 18, 2012 1 Evaluation of an Oak Tree 21821 Oakview Lane Cupertino, CA This disease can be expected to advance, however slowly, over time. The north and the south sides of this tree are not affected by this disease at this time, and the vascular flow in these areas are unobstructed. The vascular flow in these unobstructed areas explains the density and vigorous growth of the canopy. It is not the health of this tree that is compromised, but the structural integrity. In a recent lecture by Dr. Frank Rinn(California Tree Failure Report, 1-12-12, Woodside, California), several similar tree failures were presented. The size of the defect(s) and the location(s) of the defect(s) determine the potential risk of failure. The relative strength of the wood is of less importance. Based on the size and locations of the diseased areas on this tree, I estimate that the strength of this tree is reduced by approximately 20-30%. However,this estimate reflects only a static load (the tree itself, branches, and leaves)without the added pressures of wind. Dr. Rinn calculates that trees have a strength loss of up to 90%when exposed to dynamic torsion (torque) loads by wind and rain. There is no way to accurately calculate the loss of strength of this tree without sophisticated equipment measuring the pressures while under load (winds at various speeds). The fact that this tree has opposing wounds on opposite sides of the trunk significantly increases the risk. In this case, the dense canopy would likely contribute to the failure of the trunk if exposed to a significant wind load. All of this means the estimated strength loss of approximately 20-30%under a static load (standing still) may be increased to a strength loss of up to 90% during a wind and rain(additional weight) loading. I think a conservative estimate of strength loss of this tree may be in the range of approximately 70%under moderate wind loads, which in my opinion, is a significant risk. It is not practical to measure the average wind loading at this residence. Expensive sophisticated equipment would be required over a long time (2-5 years minimum). However, this residence is a two story building and the neighboring residence is a two story building. Taller buildings do affect wind speeds and movement. I think the potential for significantly strong winds in the back yard of the Hampton residence may exist during storms. What occurs during wind forces is that the lower branches bend horizontally and the top branches bend vertically (or a somewhat vertical) against the wind pressure. When the wind pressure is released, these branches whip back in a motion that we describe as "whip lash". When this occurs, greatest force is exerted on the perimeter of the trunk. If the force is sufficient, fracturing of the wood occurs along the outer edges. With each "whip lash" event, additional fracturing occurs. In cases where the perimeter of the trunk has been compromised by disease or insect infestation, the quantity of fracturing within the wood significantly increases. For this reason, the large areas of compromised wood on opposite sides of the trunk of this coast live oak tree are significant, especially because they are located on the perimeter. Prepared by Michael L. Bench, Consulting Arborist January 18, 2012 2 Evaluation of an Oak Tree 21821 Oalcview Lane Cupertino, CA Conclusion In my opinion, the potential for failure of this coast live oak tree is a realistic risk, especially if exposed to even a moderate wind load. The opinion rendered by Registered Consulting Arborist 487, Mr. Bob Booty (6-04-10) was essentially correct, but his conclusions were not adequately explained, leaving his recommendation unconvincing. Although I do consider the risk of failure of this tree to be significant, generally I do not consider the risk immediate. However, the first significant storm occurred this week and suggests a higher level of urgency. Recommendation I recommend that the request for removal of this tree be approved. Respectfully submitted, .--- ,---.- �c_____ Michael L. Bench, Consulting Arborist International Society of Arboriculture Certification #WE 1897 American Society of Consulting Arborists Member Attachment: Sketch of the Diseased Trunk Prepared by Michael L. 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