Tree diameter
The most common and most important measurement made in forest inventory is that of the diameter of the stem. Most commonly diameter measurement is carried out for stems of standing tree, and in some occasions also on stumps, branches and down woody debris. The diameter at a defined position of a tree is a length measurement from the outside of the bole, through the centre, to the opposite side of it. Diameters are usually measured with bark so that a reduction needs to be applied if only the wood is of interest.
In fact, for many calculations regarding timber volume, it is assumed that the cross section of a stem is circular, that is that the diameter be the same regardless of the direction from which it is measured. Of course, this is just a “model assumption” to describe in a simple manner the frequently fairly irregular stem cross section.
Diameter and girth measurements are probably the most important tree attributes
- because they are in most cases easily and directly measured and
- because from the diameter the basal area is directly calculated which is closely correlated to timber volume.
The diameter distribution in a stand gives a good insight into the stand’s structure and potentially necessary silvicultural treatments. The standard position for diameter measurements at standing trees is at breast height, defined at the height of 1.30m in most countries.
