The diameter or circumference is one dimension stems (trees) that determine the cross-sectional area while standing tree trunks form of logs. Even the volume to continue until the tree trunk standing or felled. To provide a deeper understanding about the diameter of a circle, below are pictures diameter and circles. From Figure 1 can be learned about the concept and the diameter of the circle, namely:
Figure 1. The diameter and Circles
Let’s just say there are two point S and the point P with a distance of r. Then point S is moved clockwise to the point P fixed to the position (1), then it will form a circular arc with an angle of α. Furthermore, continue to move into position (2). When point S at the position (2), then the distance from the initial position (0) and position (2) 2r along a straight line and the angle α formed by 180 °. This distance is expressed as the diameter of the notation D = 2r.
Point S moves back to starting position and finally resting back at the starting position (0). This means that the point S in an arc on a plane at an angle of 360 °. The arc shaped expressed as a circle. By paying attention to the concept and the diameter of the circle, what conclusions can be obtained? Along with an explanation of the diameter and circle above, then:
(A) diameter rod is a straight line connecting two points on the edge of the stem and through the stem axis.
(B) The circle (around) the rod is circular arc line length rods.
In the formula tree basal area there is value π, which amount has been a constant in the whole world, which is 22/7 or 3.14. The question that arises in our mind next is: how the value of π is obtained? To be able to answer that question, let’s look at a picture of determining the value π and the following explanation.
Figure 2. Determination of Value π
From Figure 2 can be learned about the concept of the amount of the value of π, namely:
Point S moves from the initial position (0) around the point P clockwise by a distance r unit to the farthest point, namely the position (2) to permit distance of 2r unit (D unit).
From the description of the concept of the amount of the value of π above, then:
(A) The formula for calculation of the circumference.
(B) diameter calculation formula.
Where,
K = circumference (cm)
D = diameter of the circle (cm)
In addition to the purposes of estimating the dimensions of other trees, diameter at breast height (dbh) is usually measured as a basis for further calculation purposes, for example to determine the basal area. Tree basal area is the rod cross-sectional area, so it can be expressed as:
Where,
B = basal area (cm2).
π = or 3.14.
D = diameter at breast height (cm).