Basal area is a measurement of the cross-sectional area of a tree trunk at breast height (4.5 feet above ground level). It's often used in forestry to estimate the volume of timber or the density of a stand of trees.
Methods for Measuring Basal Area
There are two primary methods for measuring basal area:
1. Using a Diameter Tape:
- Step 1: Measure the circumference of the tree at breast height using a diameter tape.
- Step 2: Divide the circumference by pi (3.14159) to get the diameter.
- Step 3: Calculate the area using the formula: *Area = π (Diameter/2)²**
2. Using a Basal Area Factor (BAF) Instrument:
- Step 1: Stand a specific distance from the tree (determined by the BAF instrument).
- Step 2: Aim the BAF instrument at the tree and count the number of "in" trees within the instrument's field of view.
- Step 3: Multiply the number of "in" trees by the BAF value to get the basal area per acre.
Practical Insights:
- Using a BAF instrument is faster for large-scale assessments.
- A diameter tape provides more precise measurements for individual trees.
- Always measure at breast height (4.5 feet) for consistency.
- Consider using a clinometer to accurately measure tree height and adjust for slope.
Examples:
- Example 1: A tree with a circumference of 50 inches has a diameter of 15.9 inches (50 inches / 3.14159). Its basal area is 198.5 square inches (3.14159 * (15.9 inches/2)²).
- Example 2: A BAF instrument with a value of 10 is used to measure a stand of trees. 15 trees are counted as "in" trees. The basal area per acre is 150 square feet (15 trees * 10 square feet/tree).
