To preserve certain mature trees within a construction site some precautions must be taken to assure that neither the trunk, limbs nor root system of the tree are excessively damaged. The root system of a tree is the most vital and the most delicate part of the plant, and the most easily damaged.
The root system extends far from the trunk, often beyond the drip-line of the tree. The fine absorbing roots, those that collect water and nourishment for the tree, are located primarily within the top eight to twelve inches of the soil. (See Figure 1) The roots and the soil in this surface layer must be protected from injury.
Any encroachment, disturbance, or compaction of the soil around the tree will damage or destroy the fine absorbing roots. Injury caused by cutting, crushing, suffocation, poisoning, or moisture stress by inundation or dehydration can result in the death of the tree. Injuries caused during construction projects may not be finally apparent for many years after the completion of the project, but can ultimately kill the tree.
The following guidelines are minimum standards recommended for the preservation of trees. These guidelines should be incorporated in construction contracts, and the details made available to all parties involved with work on the site, including equipment operators. Other guidelines and protective measures may also be appropriate, in addition tho those listed below.
- Protection Barrier: A protection barrier shall be installed around the tree or trees to be preserved. The barrier shall be constructed of durable fencing material, such as plastic construction fencing, snow fence, or chain-link fencing. The barrier shall be placed as far from the base of the tree(s) as possible, preferably at the drip-line. The fencing shall be maintained in good repair throughout the duration of the project, and shall not be removed, relocated, or encroached upon without permission of the arborist involved.
- Storage of Materials: There shall be NO storage of materials or supplies of any kind within the area of the protection barriers. Concrete and cement materials, block, stone, sand and soil shall not be placed within the drip-line of the tree.
- Fuel Storage: Fuel storage shall NOT be permitted within 150 feet of any tree to be preserved. Refueling, servicing and maintenance of equipment and machinery shall NOT be permitted within 150 feet of protected trees.
- Debris and Waste Materials: Debris and waste from construction or other activities shall NOT be permitted within protected areas. Wash-down of concrete or cement handling equipment, in particular, shall NOT be permitted within 150 feet of protected trees.
- Grade Changes: Grade changes can be particularly damaging to trees. Even as little as two inches of fill can cause the death of a tree. Lowering the grade can destroy major portions of a root system. Any grade changes proposed should be approved by an ISA Certified Arborist or a member of the American Society of Consulting Arborists before construction begins, and precautions taken to mitigate potential injuries.
- Damages: Any damages or injuries should be reported to the project arborist as soon as possible. Severed roots shall be pruned cleanly to healthy tissue, using proper pruning tools. Broken branches or limbs shall be pruned according to International Society of Arboriculture Pruning Guidelines and ANSI A-300 Pruning Standards.
- Preventive Measures: Before construction begins, fertilization of the affected trees is recommended to improve tree vigor and health. Soil analysis testing should be completed to assure fertilization with the appropriate fertilizer products. Pruning of the tree canopies and branches should be done at the direction of the project arborist to remove any dead or broken branches, and to provide the necessary clearances for the construction equipment.
Russell E. Carlson RCA, BCMA, is an internationally known Registered Consulting Arborist with more than 32 years experience. He provides expert consultation and testimony in forensic arboriculture cases, tree risk assessments, and tree appraisals, and has taught arboriculture and forensic methodology to other consultants and experts.
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