19E - RFP - STREET TREE MAINTENANCE

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any age but is most common on medium -aged and mature trees. Cleaning is the preferred pruning type for mature trees because it does not remove live branches unnecessarily. Cleaning removes branches with cracks that may fail when the interior wood dries. C. Crown Thinning: Crown Thinning includes the selective removal of branches to increase light penetration and air movement into and through the crown. Increased light and air stimulates and maintains interior foliage, which in turn improves branch taper and strength. Thinning reduces the wind -sail effect of the crown and the weight of heavy limbs. Care must be used to avoid stripping branches of all foliage at the interior of the tree crown. This practice, known as "lion tailing" disrupts the structural integrity of the tree, making it subject to limb and branch failure, especially during high winds. Thinning the crown can emphasize the structural beauty of trunk and branches as well as improve the growth of plants beneath the tree by increasing light penetration. When thinning the crown of mature trees, up to 25% of the live foliage may be removed unless directed otherwise by the City Arborist. d. Crown Reduction: Crown Reduction is used to reduce the height and /or spread of a tree. Crown reduction varies from topping, a destructive practice, in that cuts are not made indiscriminately, resulting in large stubbed off limbs that are subject to decay. Reduction is the selective removal of branches and stems to decrease the height and /or spread of a tree or shrub. This type of pruning is done to minimize the risk of failure, to reduce height or spread, for utility line clearance, to clear vegetation from buildings or other structures, or to improve the appearance of the tree. Portions of the crown, such as individual limbs, can be reduced to balance the canopy, provide clearance, or reduce likelihood of breakage on limbs with defects. While reducing a crown, tree workers must adhere to basic tree trimming practices involving limb /branch size relationships and use of the branch bark collar in avoiding the onset of decay at cut sites. e. Crown Restoration: Crown Restoration is corrective pruning used as a means to restore the form of crowns that have been previously damaged by extenuating circumstances. Restoration is the selective removal of branches, sprouts, and stubs from trees that have been topped, severely headed, vandalized, lion tailed, broken in a storm, or otherwise damaged. The goal of restoration is to improve a tree structure, form, or appearance. Properly done, this technique provides a more pleasing, unpruned natural look to the tree compared to topping or shearing. Crown Raising: Crown Raising consists of removing the lower branches of a tree in order to provide clearance for buildings, vehicles and pedestrians. It is important that a tree have at least one -half of its foliage on branches that originate in the lower two - thirds of its crown to ensure a well- formed, tapered structure and to uniformly distribute stress within the tree. City of Santa Ana Street Tree Maintenance RFP 19E-30 Page 27