Tree Protection / Critical Root Zone
The ANSI A300 Part 5 tree protection zone (critical root zone) to fence off during construction: radius = radius_factor x DBH (1.0 ft/in standard, 1.5 ft/in mature), area = pi x radius^2. The zone is set by the trunk diameter, NOT the canopy dripline -- a narrow-crowned tree still needs the full radius, so fencing to the visible canopy under-protects the roots.
Formula and source
radius = radius_factor x DBH; area = pi x radius^2 (radius_factor 1.0 ft/in standard, 1.5 ft/in conservative/mature).
Tree protection zone / critical root zone (ANSI A300 Part 5; ISA critical root zone), by name.
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