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HomeMy WebLinkAbout11-19-2018 Item 4, Cochran (2)WRC �-IVE15­— NOV 2 1 2018 i MEMO �3�..c CITY CLERK To: Architectural Commissioners Richard Beller, Brian Rolph, Micah Smith, Angela Soll, Christie Withers, Vice Chair Amy Nemcik, and Chair Allan Root From: William Cochran, 43 Buena Vista Drive Subject: Landscaping, 40 Buena Vista Drive Date: Wednesday, November 21, 2018 The document attached to the earlier version of this message (11/20/18) was the wrong document. Please forgive my carelessness. The correct document is attached as hard copy to this memo, and consists of a report made by an ISA Certified Arborist in late 2015. 1 think you will find it useful in your deliberations, especially the short Conclusion on the fourth page. Respectively, William Cochran 43 Buena Vista Drive GREENVALE TREE COMPANY Purpose: To explore the feasibility of planting, viability, maintenance and fire safety regarding Oaks to be planted along the back and sides of a proposed residence on Buena Vista Avenue in San Luis Obispo. Background: Local residents in the neighborhood of Buena Vista Avenue are concerned with a proposed residence that is to be located on a very steep lot. In the proposal it has been stated that large Oak trees are to be planted to screen views from the back of the residence (toward Loomis) and the sides. Concerns have arisen about the ability to plant large trees on the slope and the viability and maintenance of them should they be planted. Visibility — Because of the steep slope and the height of where it is to be built the structure will be highly visible from Highway 101 and the roads and properties below including areas off Monterey Street and San Luis Drive. There has been some discussion of a 101 scenic highway through the area and some restrictions concerning buildings along the view corridors as cars approach San Luis Obispo from Cuesta Grade. Mitigation for this structure was in part to plant trees to screen the residence. Slope and soil - The lot is extremely steep. Much of it approaches, or perhaps exceeds, 45 degrees. The soil is loose alluvial soil and not far below this is rock. This type of soil has a high capacity to slip and erode. Exposed rock from cuts throughout this area shows signs of underlying serpentine rock. There is very little organic matter in this soil. Currently the area is grassland with Oaks below along Loomis. There is one Oak above. very close to Buena Vista Avenue. Access to the lot — The lot runs between Loomis (below) and Buena Vista. Access for trees and equipment to be brought onto the property is primarily from Buena Vista as the current plan exists. There is no driveway but a steel "bridge' linking the garage to the road. Below, on Loomis, there will be no feasible way up to the area where the trees are to be planted due to the steep terrain. Buena Vista Avenue is about 1'/z lanes at the lot frontage which makes this area narrow. Size of trees — Other than "large" trees being planted I have no reference as to what size. I will assume that large would indicate a boxed tree and 48 -inch would be considered as "large". For this report, Trees or Oaks in regard to planting and/or this planned structure are considered to be a 48 -inch box. keasMUILy of Planting The container measures 48 by 48 inches. Oaks would likely be 8 to 12 feet in height. Normally trees of this size are either craned in or a large, construction -type forklift is used to lift them off the truck and with the aid of rigging lower them into the planting holes. Due to the steepness of slope and lack of rooin for a crane or fork lift neither can be used. 'to get the trees downhill winches and rollers would need to be used to slowly get the boxed trees into position. Holes would have to have ramps dug out on one side so the trees could be slid down into the planting holes. Time and care will need to be taken to maneuver these trees down slope into place and to plant them. Coast Live Oaks in a 48 -inch box will grow 8 to 12 inches per year on average. They will, on average, reach a height of 65 feet. Width on a Coast Live Oak varies widely from 20 to 80 feet. Plants should be planted 30-40 feet apart. n•;i: v cl,c„lj Tint hn rlantrd rinmr than thirtJ feet frnm the stmoftire, utilities or drainage. The further downhill you plant an Oak the more it will need to grow to become a screen. Planting trees that are 8-12 feet high would have very little screen impact on the down slope side of the residence. It would take many years before Oaks could significantly screen this residence. LGL J W2llri LillVUgll aviiiV iiiCLlu. Start with a tree 10 teet tall. You plant this tree 30 feet downhill from the closest footing. Drop in elevation from edge of footing to planting site given 45 degree slope 30 feet Elevation from footing to roof peak 39 feet Distance (vertical) from ground where tree is planted to roof height 69 feet Subtract 10 feet for our original tree height Divide the above number by 8 - 12 inches per year 59 feet 59 to 74 years This is the nunnber of years it will take to have an oak grow to be as high as the roof line and ettectively screen the residence. Viability nit_ tr(-rc nrPfer Ince vAl drained soils lots of organic matter and a healthy rhizosphere. The rhizosphere is an area of soil (10 to 16 inches deep) that contain microorganisms such as bacteria, beneficial fungi and larger organisms such as worms and bugs that break down organic matter. Without a healthy rhizosphere Oaks are subject to stress, disease and pests. In a practical sense it is the lack of a suitable rhizosphere, or conditions to create one that limits the viability of an Oak. The soil on this slope is alluvial with underlying rock. Rock in this area tends to have plentiful serpentine in it. Serpentine rock/soils tend to have high levels of magnesium and heavy metals and are low in Calcium. Some plants adapt and some even thrive in serpentine soils. Oaks have adapted to serpentine soils but these oaks are native coming up from seed. They are also much smaller and more sparse than oaks that grow on other soils. Also the micro-organisms needed for Oaks tend to fail to colonize in serpentine soils as heavy metals can be toxic to them. While the soil here has a loose upper surface there is rock not far below. Two very opposite things are likely to happen in the establishment of Oaks on this lot due to the underlying rock. The underlying rock will need to be chipped away to make a basin for the planting hole. This is a suitable situation when water can be controlled. But when we have wet years water will pool in the rock planting hole and the oak will likely die or become stunted due to rot or root asphyxiation. If deeper soil is found where the planting can be done in loose soil likely the opposite is true. Water will flow through the soil rapidly and hit the underlying rock where it will then flow downhill. This perennially dry soil will lead to poor estahlishment and a stunted tree. Both the serpentine soil and underlying rock is the reason we find no Oaks growing on this hillside. The grasses and other annual, shallow rooted plants can survive and grow but establishing an Oak to full potential and vigor is improbable. Maintenance. Oaks are wonderful in natural settings but can be a great expense and a big mess in our landscapes. Constant leaf drop, twig dieback and dropping acorns don't just make a mess they can be fire hazards. More to the point it is dead leaves and twigs (and sometimes branches) that remain on the tree that can become fire hazards. Oaks are by nature fire resistant, That is they can recover and re -sprout and in doing so the fire eliminates the dead and weak branches as well as pests. Near a residence the fire marshal requires all combustibles within 30 feet of a structure to be removed. Trees "shall" be pruned of all dead limbs, combustible debris be removed and canopies lifted to prevent fires from coming up from the ground into the canopy. In general, to meet this requirement oaks will need frequent pruning (every two to three years). Because of the type of soil and terrain the oaks should be watered the first three years. In dry years the Oaks will need supplemental water to survive perhaps on a monthly basis. Failure to maintain the Oaks through watering can lead to severe dieback, disease and it can become a fire hazard. Fire Safety On the lot in consideration the terrain will pose a problem ►t'a lire occurs. l'ire moves uphill taster than downhill as the heat creates air currents pushing flames uphill. Low canopies are subject to being burned. Oaks which naturally grow with extensively wide but low canopies would be subject to this type of fire situation. Any tree on this steep of a slope is going to need its canopy elevated for fire prevention alone. Oaks do not do well, and in fact are subject to disease and pests, if maintained at high canopy heights. Higher canopy heights will also expose the house to view, negating the screening of the home. Because Oaks sheds debris continually, maintaining fallen leaf and twig litter on the roof and near the building will need to be done several times a month. Oaks if planted would need to be planted further away ti-om the home to prevent dry leaf' and twig debris from accumulating on the roof or near the building. The fire plan states no combustibles within 30 feet. Oaks will accumulate deadwood on a consistent basis. When we read that Oaks are "fire -proof' it does not mean that they do not burn. When Oaks are ignited they burn very well if there is deadwood, dead twigs and dry leaves. The term "fire -proof' in the case of Oaks means that the Oak can recover and grow after a fire. Oaks planted nearby this structure then would need to be regularly "cleaned" of combustibles on average every 2-3 years to make the trees less combustible. The rest of the landscape would also need to be designed and planted with fire in mind. Certainly on this steep of slope plantings would want to be made with erosion control and slope stabilization in mind. However, fire safety will need to dictate what actually can be planted and what materials can be used. Conclusion Considering all the factors (slope, type ot'soil, need to screen the view within a reasonable amount of time), oaks may not be a good selection for this property. Having said that, there probably is no tree that will meet all requirements given the challenges posed by the conditions on this lot. Sincerely, Clines Stier, ISA Certified Arborist, #9262 "Diagnosis was made with observation, history and sound arboricultural and horticultural knowledge. It is always possible that other, or different probleals etist that play contribute to the decline and death U- plants, Faither cwIlliatiLij1111ay be warranted if the steps above do not work. Pathology tests and other lab analysis are available.