The Critical Root Zone
City code requires that proposed developments demonstrate that trees are preserved to the maximum extent reasonable and feasible. Tree preservation is effectively defined as root system preservation; a Critical Root Zone Area (CRZ) is assigned to each tree, based on trunk diameter size. A minimum of 50% of the CRZ is required to be left undisturbed to achieve minimal conformance with the regulations.
Trees are depicted on plans with a CRZ circle centered on the tree base location (i.e. a twenty-inch diameter tree is represented by a 40-foot diameter circle).
Here is the formula: Tree diameter in inches X 2, then convert to feet = CRZ diameter.
The CRZ circles are superimposed on the proposed plan improvements so that review staff can discern the extent of disturbance proposed near existing trees. Tree types and sizes are also provided. Trees that are removed are generally required to be replaced at a sliding ratio determined in part by the overall extent of tree removal proposed.
back to City Arborist page