Q: What's the difference between Southern oak and Appalachian oak? If I buy upper-grade Southern oak, will it yield the same as lower-grade Applachian oak?
A: First, let's consider the differences between these two oaks, and I'll throw in Northern oak too. I have taught for many years that the lowland oak (which does indeed dry differently than upland oak and has several other processing differences) is any oak that consistently has annual growth rings more than 1/4-inch apart. In other words, to get such large annual growth, the tree had to be growing in a warm, long-growing-season site with adequate water. Note, however, that I did not use the term "Southern" but rather used the term lowland. There are quite a few lowland sites (where it is more difficult to process lumber) in the Appalachian regions and even in the North.
Actually, there are 80 species of oak that we classify into two groups - red oak and white oak. Some of these species like wet, warm sites to grow in and others prefer well drained, colder areas. As a result, when we switch from lowland to upland, we are almost always switching species of oak. It may be surprising how much variation there is between species within the red oak or white oak groups.
The grades applied to any of the three oaks - Northern, Southern, and Appalachian - are identical. As the hardwood grades are based on the amount of clear area in a piece of lumber, the clear area in oak from any source will be the same if the grade is the same.
As Southern oak is dried in a warm environment, and as there are fewer pre-dryers in the South, the lumber is more subject to a risk of staining. Further, lowland oak generally shrinks several percent more than upland oak during drying. Lowland oak is also often subject to a higher risk of developing surface checks - it is a characteristic of the wood itself, perhaps related to the increased shrinking. Therefore, the yield from lowland oak that was graded green and then dried may be less than upland oak, due to increased drying defects.
If lumber is re-graded after kiln drying and any below-grade pieces removed and any shrinkage accounted for by remeasuring the footage, there will be no yield difference between upland and lowland. (Reread this paragraph, as it is important.)
Comparing upland and lowland, lowland often (but not always) has a redder color, more color variation at times, more dramatic ring patterns, less warping, more graying in the sapwood, higher density that may negatively affect machining and gluing, and wider and longer pieces of lumber.
Because of the higher humidity in the South, it would not be uncommon to find that kiln-dried lumber stored in uncontrolled conditions would have substantial moisture regain, perhaps making it too wet for some uses.
Of course, the most obvious difference between Southern and Appalachian or Northern is the price. Lowland is often quite a bargain if it has been regraded and remeasured after kiln drying.
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