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<br /> <br /> <br />Calculating the CRZ: <br /> First you need to calculate the tree’s Diameter at Breast Height <br />(DBH). DBH can be measured using a caliper measuring tool, or for <br />trees that are too large, DBH can be measured by dividing the tree’s <br />circumference by pi (π). <br /> Diameter = circumference / π (3.14) <br /> <br /> The Critical Root zone extends from the trunk of the tree to its <br />drip line, or to a distance of 1.5 feet per inch DBH, whichever is <br />greater. <br /> <br />DIAMETER BREAST CRZ = Diameter * 1.5 feet (18 inches) <br />HEIGHT (DBH): The diameter of the trunk of a tree 4.5 feet above the existing grade <br />at the base of the tree. For trees that have branches or swelling at <br />4.5’ above grade that interferes with measurement or for multi- <br />stemmed trees refer to Table 1 below. <br /> <br />TABLE 1: HOW TO MEASURE DIAMETER AT BREAST HEIGHT (DBH) <br /> <br />Standard Tree <br /> <br />For those trees on a site that are at least 6 <br />inches in diameter at a height of 4.5 feet <br />above the existing grade at the base of the <br />tree. For trees on a slope, measure on the <br />uphill side of the tree. <br /> <br /> <br /> <br />Tree has branches or swelling at 4.5’ <br /> <br />Measure DBH below the branch or swelling <br />immediately below where branches cease to <br />affect diameter of the stem. Record the <br />height at which the diameter was measured. <br /> <br /> <br /> <br />Multi-stemmed Trees <br /> <br />If a tree splits into multiple trunks below <br />4.5’ above the existing grade, the DBH shall <br />be considered to be the measurement taken <br />at the narrowest point beneath the split. <br /> <br /> <br />8 <br /> <br /> <br />