2.2: Determining Tree Height
1. Total height . Total height is the height of the tree from its stump to its tiptop (Figure 2.1). A one-foot stump is standard, although there are times when another base is used.
2. Merchantable height. Merchantable height is the height of the tree from its stump to a diameter at which the trunk is too small to be marketable (Figure 2.2). This “merchantable top” diameter is commonly 6” or some percentage of a diameter low in the tree, such as dbh (see Chapter 3). “Taper height” is very similar, without the emphasis on the top diameter being the end of merchantability.
The principles and techniques for measuring any of these heights are essentially the same. We will focus on total height in this text.
So how in the world do we figure out how tall a tree is? Surely we don’t climb each tree with a tape or cut every tree down to measure it. We need a simple, straightforward, and quick way to measure tree height to make it a feasible part of our inventory data. Here is the easiest way for good precision:
In determining tree height, we presume that the tree is perpendicular to the ground. Therefore, the tree makes a right angle with the ground, and a right triangle can be drawn from it. The triangle’s three sides are: 1) the tree, 2) the horizontal distance along the ground, and 3) an imaginary diagonal line running from the top of the tree to the ground. Likewise, the tree’s height can be considered the rise and the horizontal ground distance the run. (Sound familiar?) If we can measure a horizontal distance from the tree to a place where we can see the tree’s top, we can determine the tree’s height using %slope (Figure 2.3).