Tree Protection During Construction and Development
This domain tests how trees are protected through design, demolition, and construction, and how damage is documented and valued.
Core rules
- ANSI A300 Part 5 covers managing trees during site planning, development, and construction.
- The critical root zone is commonly set at 1 to 1.5 ft of radius per inch of DBH, with a minimum radius; the tree protection zone is the fenced area that keeps equipment, storage, and grade changes away from it.
- Fencing goes up before demolition and stays until final landscape inspection; signage and a pre-construction meeting with the site supervisor matter as much as the drawing.
- Prohibited within the TPZ: grade cuts and fills, trenching, paving, soil compaction, material storage, and equipment washing.
- Acceptable techniques include directional boring or tunneling for utilities, air-spade root pruning, and temporary mulch over the root zone.
- Damage is valued with the ISA/CTLA trunk formula method, using species rating, condition, and location factors.
Worked example
A 20-inch oak has a TPZ radius of 20 ft at 1 ft per inch of DBH, an area of about 1,256 square feet. A sidewalk must cross the zone. Rather than trenching 6 ft from the trunk, the plan specifies directional boring at 4 ft depth beyond 10 ft from the trunk, an arborist monitoring during drilling, and hand excavation near roots. The cost premium is charged to the project and documented in the tree protection plan before permits are issued.
Traps
Treating the dripline as the TPZ. Approving a temporary storage area inside the fence. Ignoring small grade changes, which kill roots as surely as cuts. Forgetting to record pre-construction condition, which forfeits later damage claims.