The main stem is the most useful part of a tree for conventional wood products such as pulpwood, posts, poles, and lumber. Defects that reduce the total volume of usable wood in the tree include sweep, crook, cracks, decay, forks, and imbedded objects (Figure 2-3). Your forester will note the percentage of defect in each tree stem by product type. This percentage is then deducted from the overall estimate of tree volume. Because tree diameter decreases with increasing height in the tree, a defect occurring near the top of the tree will require a smaller percentage volume deduction than a similarly occurring defect near the base. Percentage deductions for tree defects are best estimated by a forester and recorded on a tally form. If the entire tree is unusable because of an excessive amount of defect, your forester will not measure it for wood products. This is a cull tree, and while not usable for wood products, it can be valuable for wildlife habitat.
Defects such as burls, bird pecks, dead limbs, insect holes, live limbs, and knots will not affect the total volume of usable wood, but they will reduce wood quality, or grade (Figure 2-4). Tree grade influences the types of products that can be made from a tree and therefore the stumpage price. Higher grade trees have fewer defects.