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A common meaurement for determining tree size is diameter at breast height, (dbh). This is defined as the average diameter of the tree in inches measured at a point 4-1/2 feet above the ground on the uphill side of the tree. Dbh can be determined by dividing the distance around the tree by 3.14. However, dbh is usually measured by use of specially designed measure sticks, tapes, or calipers.
It is most essential for the forest landowner to be able to determine species of the individual tree. There are many excellent tree identification books available. Time spent learning to identify trees is certainly not wasted because the growth characteristics, site requirements, and log or lumber values vary widely among different tree species.
Another important characteristic of the timber stand is the degree of stocking, or how fully trees utilize the existing growing space. This usually is expressed as number of trees per acre or basal area. Basal area is the number of square feet per acre occupied by tree stems at breast height. A stand should be managed to achieve a fully stocked stand. This is a stand in which trees are neither too crowded nor too widely spaced for maximum growth per acre. Over the life of the stand, the number of trees per acre will decrease drastically as the slower growing trees are crowded out of the stand by more dominant trees. A stand which has just been reproduced may have several thousand stems per acre while the stand when ready for harvest, will probably contain less than 100 stems per acre. (See Appendix, "Trees Per Acre").
Quality of the individual tree may range from a highly valuable prime veneer type tree to a hollow tree with no value whatsoever. Tree quality is primarily determined by the amount of crook in the stem, number and location of knots, presence of decay, and marketable length of the stem.
Benefits obtained from timber in the forest are determined to a large extent by the rate of growth which is in turn determined by the stocking of the stand and the quality of the site. Although diameter increases fastest in young trees, there is no sawtimber volume until trees reach 10 to 12 inches dbh and very little sawtimber value until well past this point. A study in the Appendix of "Tree Value Increase", "Yield Tables", and "Growth Tables", will show that the most profitable size at which to harvest timber is neither at the minimum marketable size nor at biological maturity but at a point between after the annual volume or value increase reaches a maximum. This point is referred to as economic maturity. Accurate determination of this point and preparation of a cutting budget requires growth measurements. These are usually done either by measurement of annual growth rings or by comparisons of diameters and volumes over a period of time.
The primary objective of timber management is to produce the most volume of high quality timber of desirable species possible in the shortest amount of time. This is usually accomplished by efforts toward regulating the stocking and composition of the stand. Volume and stocking tables such as those on the Timber Inventory Worksheet are helpful in planning these efforts.
Besides inventory of his land and timber resources, the wise woodland owner will want to consider and inventory any minerals such as coal, oil, gas, etc., present on his land. Improvements to the land such as buildings, established roads, developed recreation areas, lakes, ponds, etc., should also be listed and valued in the inventory. Although difficult to evaluate in monetary terms, intangible values may, in some cases, be of over-riding importance. These include aesthetic, recreational, and historical values.