Loading...
HomeMy WebLinkAboutAttach 3 Ltr from J McNeilJanuary 12, 2004 Alex Loukianoff 12 Kirk Court Alamo, CA 94507 SUBJECT: Effects of proposed construction on existing trees at 11299 Rolling Hills Drive, Dublin. You requested that I review the drawing you furnished, and provide comments on construction impacts, if any, and any methods of reducing any impacts. The attached site plan is a scan, at 20 scale, of one provided to me by you. Construction of the home, as shown, will require substantial pruning, for clearance to the building. This pruning is within the tolerance of the tree, as is expected encroachment into the root zone. The pruning will, however, alter the form of the tree immediately against the house. SITE The lot is a "flag" lot, behind the adjacent home. About 25% o£the area of the lot, to the east, is an extension of the pad graded for that home. At the west edge of the pad the terrain reverts to the historic slope, about 2:1, with flatter or steeper variations. About 25 feet from the top of the slope, and 35 feet from the north property line is one of two existing valley oaks on the site. This oak, numbered 353, by an aluminum tag, has four trunks, diverging close to the ground, of 19.9, 18.7, 15.3, and 13.2 inch diameters, respectively. It's health is characterized as fair to good; annual shoot elongation, a measure of vigor, is about three inches all around. A highly vigorous valley oak might extend 12 inches per year. However, the canopy is full, well foliated, showing no signs of decline. The second valley oak, 20 feet downslope and slightly north of #353 is generally outside the scope of this report. The soil of the level pad, at an elevation of about 111 feet, is compacted. Presumably the slope extended to a higher elevation and was truncated at pad level. The soil on the slope outside the extension of the tree canopy is exposed, and the tree, compact and solid outside the canopy. Roots will more likely be found 2004 3 M~JLTE~J ~:Oq~qr o FLE~J~MT MILL ¢./JLIJ"O~lfl~ 94523 Certified Axborist # WC0102 Cali£omia State Conlm¢lors License # 452248 (Tree Care C-61 13-49, Landscaping C-27) Registered Consulting Arborist #299, ASCA '-" '"".'mvttNT Loukianoff Tree/Construction Report Page 2 11299 Rolling Hills Dr compact in feel. The soil within the tree canopies is deeply covered by natural mulch, years of fallen debris from the trees, and is very soft, easily penetrable, a good habitat for roots. Some of this soil has sloughed downslope against the trunks of the trees. Particularly, there is slight fill against the uphill side of tree #353, and there appears to be a slight raise in grade all around the second oak. This soil should be removed, as we discussed, to expose the tops of buttressing roots, to a distance sufficient to discourage soil from immediately falling against the trees again. Tree canopy spread to the south and east was measured, and found to be consistent with that shown on the attached drawing. CONSTRUCTION Most of the proposed home will be constructed on the slope south and slightly east of tree 353. A conventional stepped foundation will be utilized. Grading is not expected outside the building footprint on the nortL side, where it might affect the tree. As noted above the soil on the slope where the house will be located is relatively bare, facing to the WSW, where it receives direct afternoon sun, and appears to not to provide the habitat ideally colonized by oak roots. Some oak roots may occupy this zone, but is appears fundamentally hostile, inconsistent with the environment preferred by the trees. It is much more likely that a high proportion of the oak roots will be found where the soil is looser, and there is more organic matter, under the tree canopies. The closest approach of the building to the tree is a "popout" section, almost 15 feet long, that extends to within about 18 ½ feet of the center of tree 373. This will encroach about four to five feet within the tree canopy. Downslope, a ten foot wide deck will extend about seven feet into the canopy. Conventional foundation will support the popout section, while the deck will be built on piers. Figure 2. This photo is centered along a line representing the side of the "popout' section of the house, the orange line. Joseph McNeil January 13, 2004 Loukianoff Tree/Construction Report Page 3 1299 Rolling Hills Dr You should expect that soil four feet outside the foundation (toward the tree), will become compacted during construction. There is not practical way to avoid this. Access to move material around the house, and finish the exterior will require repeated walking. Therefore, a temporary zone of encroachment will extend four feet closer END OF THIS LIMB I 1/2 INCH 5INCH 7INCH 6INCH 4INCH to the tree from the side of the foundation, along the entire north side. The deck should have...,,~;"~,- effect on the root zone. On the u~)hill side it is within six inches or a foot of the surface, and will be about four feet elevated on the downhill side. It will be permeable, and when complete should have a minimal effect on tree roots. Figure 3. The orange line to the lower left is again the edge of the popout. The red arrows indicate limbs that must be removed or cut back to accommodate the popout. (This is not a specification for pruning. It is a typical representation of likely required pruning) The limb at the top that will require cutting back 'the end of this limb', may require minor or major pruning, but should not have to be removed entirely. The yellow arrow designates approximately the area where limbs of 4, 3 Ya, and 2 Y~ inch diameter will have to be removed for deck headroom. I understand that the city of Dublin requires clearance of five feet between the building and the tree. Pnming will have more impact on the tree than encroachment over the root system, in my opinion. The pruning necessary to achieve five feet of clearance is quite substantial on the southeast side of the tree, although it represents a minority of the foliage overall. Similarly, because limbs on the south side of the tree reach nearly to the ground, substantial prurdng will also be required for headroom over the deck. Limbs to six inch diameter and larger must be removed from the tree. (See Figure 3) MANAGEMENT OF IMPACTS There will be a moderate overall impact to the tree from construction as proposed. Injury to the root system., overall, is expected to be slight. Most roots should be expected to inhabit the hospitable zone under the tree canopies. Root location cannot be predicted accurately, and while it is possible that roots from the tree exist on the slope under the proposed building footprint, it should be remembered that this slope is physically hard, faces directly into the summer/fall afternoon sun, and is prone to desiccation. I would not expect location of the house over this area to greatly impact roots from the tree. I consider the encroachment into the more favorable root zone under the canopy to be relatively minor. However, it will be important to limit any activity to within four feet of the house. Joseph McNeil January 13, 2004 Loukianoff'Free/Construction Report Page 4 1209 Rolling Hills Dr Pruning will visibly change the tree canopy against the house. Pruning also constitutes physical injury, as food producing organs (leaves) are lost and mechanical openings are created, at each of which the tree must expend energy to resist invading decay organisms. The combination of root and branch injury is within the capacity of the tree to tolerate, in my opinion, although less encroachment would be desirable, in this case largely because it would reduce the necessary pruning. Tolerance of the tree to this injury is highly dependent upon adherence to the guidelines below, which will prevent or mitigate unnecessary injury. Damage to trees may occur directly, from mechanical injury to roots, trunks or limbs, or more indirectly, if soil characteristics, such as density, soil atmosphere or moisture content are altered. Manifestations of these injuries may occur immediately, or may be delayed for a number of years, resulting in progressive decline. Several strategies may assist in reducing impact to this tree: Fencing. Many tree roots on most sites may be in the top 18 inches of soil, a zone which is easily altered by even minor grading, trenching, or material storage. Such alterations may occur at any time during construction activities, even from foot traffic. Soil may become compacted, soil oxygen may then become easily depleted, drainage patterns upon which trees have become dependent may be altered, so that trees become drought stressed. A protected zone must be established. Install sturdy temporary five foot chain link fence, on driven posts, four feet away from the side of the stepped foundation on the northwest side of the house, and to the edge of the foliar canopy along the existing pad, at the top of slope. This fencing should be in place at the beginning of layout, and should stay in place throughout construction, including exterior finish. It will be necessary to move it near end of construction, to build the deck. Be sure that all contractors and subcontractors understand the purpose and importance of the fence. Mulch. Existing natural surface mulch under the tree appears adequate at this time. Mulch serves a number of beneficial functions, including moderating temperature, retaining moisture, and fostering an environment of interrelated fungi, bacteria, small arthropods and worms, where roots find the moisture, nutrients and oxygen they need to thrive. When construction is complete the soil between the building and the fence will have become compacted. Apply five inches of chipping debris from a tree service over this area (not immediately against the house) and retain it there. The area inside the fence should be re- evaluated at that time for the need for supplemental mulch. Joseph McNeil January 13, 2004 Loukianoff Tree/Construction Report Page 5 1299 Rolling Hills Dr Irrigation. Native oaks are not compatible with heavy irrigation, but do appreciate some supplemental irrigation during the dry season. It certainly would be beneficial for a tree recovering from construction trauma. This irrigation could be three applications, every six weeks, starting about six weeks after the last soaking rain in the late spring. I suggest a soaker hose from the top corner of the proposed popout section of the house, about 20 feet north along the slope, allowed to run for four-six hours, then repeated six-eight feet down hill. A third application, again four-six hours, could be made about six feet downhill of tree 353, unless water is observed at the surface, from previous uphill irrigation. Landscape. I suggest no landscaping under these trees for a period of three years after construction. If you wish to landscape later this should be with plants of similar cultural requirements to the oaks. The California Oak Foundation has a booklet, for purchase, with valuable landscaping irrigation.! Any plants installed should be irrigated by drip irrigation only. Drainage. Drainage from the yard, patios, walks, or house should not be directed so that it flows into the root zone, particularly close to the tree trunks. Material disposal. Be sure that contractors understand not to wash out paint buckets, concrete or stucco mixers, or other containers, or dispose of other soluble or liquid debris within or above the root systems of either tree. All pruning should be done by a Certified Arborist2 or Certified Treeworker. I can refer you to compliant companies, if you wish. No pruning should occur other than removal of dead limbs and that necessary for building clearance. Further questions may arise regarding this project. Please contact me if they do. Joseph McNeil Certified Arborist #WC0102 Registered Consulting Arborist #299, ASCA Contractors Lic. #482248 (Tree service C-61 D-49, Landscaping C-27, inactive) ~ Compatible Plants Under and Around Oaks, California Oak Foundation, 1212 Broadway, Suite 810, Oakland, CA 94612, (510)763-0232) 2 The International Society of Arboriculmre administers a voluntary certification program. Certified Arborists are listed at http://www.isa-arbor, com/arborists/arbsearch.html / Treeworker certification (a less stringent certification) is currently performed by the Western Chapter of the ISA. Lists are available from WCISA, P.O. Box 255155, Sacramento, CA 95865 Joseph McNeil January 13, 2004 / ~ I×~ I /× / /1 I/i// t (N) RETAINING WALL / / t1~ // !/, ii/' 30" OAK OAK #353 CONC~ DRIVEWAY ~[/_ .......... TURN- AROUND SCALE, 1" = 20' / / x\ \ \