3.1 Why Tree Diameter?
In addition to satisfying our innate curiosity about how big trees are, measuring the diameter of trees can tell us quite a bit about a forest stand. As we will discuss in a later chapter on “Stand Characteristics,” there is a direct relationship between tree diameter and tree crown. The bigger the tree’s diameter, the greater the amount of foliage it has. Tree diameter data can provide essential information about crown competition, stocking levels, and forest health. Stand management decisions, such as when and how much to thin a stand, rely heavily on data derived from measuring tree diameters. In addition, tree diameter is needed in order to determine a tree’s wood volume.
Look at the “diameter distribution curve” in Figure 3.1 below. Without having ever been to this stand, what can you infer about it by looking at the graph? The curve indicates that there are many small diameter trees around 14”, a group of large trees around 32”, and a smattering of trees with diameters over 50”. Do the groupings indicate different age cohorts? Is the stand approaching an old-growth condition? If we look more closely at the data, we see that the small trees are shade tolerant species, and the less tolerant Douglas-fir tends to be in the larger size classes. What might that tell you?