Radial or tangential? Hardwood or softwood? Springwood or summerwood? Ring porous or diffuse porous? Let’s demystify some of the terms that foresters and wood scientists use to describe wood.

Wood sections

Wood is an organic material composed of cells. These cells are elongated, hollow and generally oriented either up and down the tree length, or from the center of the tree out to the bark. Because of these orientations, woods are best studied in one or more planes, and, depending upon which plane a log is sawn, can yield greatly different patterns in the lumber.

The most common plane wood scientists use to tell different tree species apart is the cross-section, or view of the stump or trunk as the tree is cut (Figure 1). This is also how the growth or annual rings are most easily seen.

Figure 1. Woods are studied from the cross-section, the radial section, or the tangential section of a tree.

The radial plane, or the view from the center of the tree out to the bark may also be helpful. The ray tissue is apparent on this plane. Ray tissue is responsible for moving water, nutrients and other substances laterally in the tree (as opposed to xylem and phloem tissue that moves materials up and down the tree). Rays may be wide or narrow and provide a distinctive fleck in some woods.

While less useful in identifying a wood, the tangential plane exhibits the grain of the wood, as it is the view parallel to the growth rings in the tree.

Speaking of grain, different grain patterns in lumber results from how a log is cut. If the log is cut radially to the rings, then quarter-sawn lumber is produced. If the log is cut tangentially to the rings, the resulting boards are referred to as being plain-sawn. Usually, both types of boards are produced from a single log. However, if the goal is to attain the highest yield of quarter-sawn material from a particular log, then the milling cost goes up (as well as the price per board) because more time is spent positioning the log to ensure the maximum number of radial cuts.

Figure 2. Lumber can be cut from a log in two distinct ways: radially to the rings, producing quarter-sawn lumber (A); and tangentially to the annual rings, producing plain-swan lumber (B).

Hardwoods and softwoods

Everyone has heard the terms hardwood and softwood. Botanically, the hardwoods are Angiosperms, or the species classified as broadleaved trees. Softwoods are gymnosperms, the species classified as conifers, which are usually cone-bearing trees. It is important to remember, however, that the term hardwood or softwood is not a reliable guide to the hardness of the wood itself. Hardwoods, with a few exceptions, lose their leaves in the fall or during the winter. Softwoods generally have needle-like leaves that remain on the tree throughout the year. There are only four softwoods native to Missouri: shortleaf pine, eastern redcedar, baldcypress, and Ashe juniper.

Springwood and summerwood

All trees that grow in Missouri exhibit annual or growth rings; some rings are more distinct than others. Cells and growth rings are most clearly seen on the cross-section of the wood if clean cut with a sharp knife or sanded with a medium grit piece of sandpaper.

Annual growth rings are generally divided into springwood (early wood) and summerwood (late wood). It may not be readily apparent where one ends and the other begins. Springwood consists of the larger cells produced first in the spring, while summerwood (the later and smaller cells) follows until the tree becomes dormant in the fall. In some species, there appears to be color differences between springwood and summerwood. This is because the transition from springwood to summerwood is abrupt.

Figure 3. This cross-section of white oak clearly shows the linear wood rays (A), the large springwood pores (B), and the finer summerwood pores (C). Annual rings, formed by the springwood pores, are clearly shown.

Ring porous vs. diffuse porous

The last wood characteristic we will discuss is pores. Hardwoods have them and softwoods do not. Pores are the large cells in hardwoods which transport water and dissolved materials. Often the pores will be quite large in the springwood and decrease either abruptly or gradually in size into the summerwood.

The abrupt transition from large thin-walled in the springwood to smaller thick-walled cells in the summerwood is often clearly seen, and this feature defines the wood as being ring porous. Oak is a good example of a ring porous wood.

On the other hand, if the large pores are dispersed evenly throughout both the springwood and summerwood, the wood is then called diffuse porous, even though you may clearly see the annual rings. A good example of a diffuse porous species is maple.

Understanding these basic wood technology terms should add to your pleasure and appreciation in using and enjoying the trees in your woodland.