Q: We are having a discussion here regarding what part of the season is best to cut a large white oak tree for further cutting up into dimensional columns, rafters and roof decking, as well as interior cabinets and furniture. Our timber guys say it doesn't matter. Our historians and National Park Service contacts say the tree should be cut in the winter with the sap down, then de-bark, let dry the rest of the season and cut it up late spring for use in mid to late summer. Some are worried that more cracking will occur if cut with the sap up and full of moisture. I always thought that when the pioneers cleared their lands and used the wood they would girdle the trees after the sap was down, then cut them when they could get to them in warmer weather, sap and moisture then is not a problem. I also have some concerns if we buy wood instead of cutting it, would we potentially bring in pests or disease that is destroying oaks elsewhere?
A: Your own "timber guy" is correct. The moisture in a tree is the same, winter to summer. However, as anyone who taps maple trees and makes syrup knows, in the springtime, the sap is flowing. Yet this flow does not affect drying.
What is important however, is that dark-colored fungi that discolor the sapwood are much more active when the wood is warm. So, fresh wood cut in the winter has little risk of fungal stain activity. Wood cut in the spring or summer has a much higher risk, as it is warmer outside. Most early European settlers to North America girdled the tree (removed the outer wood that would conduct liquids to the leaves) whenever they had time; in the winter, they tended to have more time than during the warmer months when they were tilling and planting. Today, when we cut wood in the warmer time of the year, we must move rapidly to avoid fungal damage. This means saw the logs, stack the lumber and begin proper drying ASAP.
Regarding cracks, wood that dries slowly, which will happen at cold temperatures, is much less likely to check and crack, compared to wood that dries quickly, which will occur when temperatures are warmer. In addition to temperature, humidity is a critical factor as well - low humidity means fast drying and a high risk of checking and cracking. Oak lumber sawn in warmer months must be handled correctly so that the wood does not dry too quickly. This proper handling may including using plastic mesh fabric to partially cover the pile to slow down drying, or using sheds that will restrict air flow and therefore drying. Some people refuse to take the extra care needed in the warmer months, so they purchase oak only when it is cool. This is perhaps shortsighted but it does work.
With respect to insects, the insects that are destroying oak trees will not be active once the tree is cut. Nevertheless, you do want to be careful that you do not introduce any insects into the air-dried or kiln-dried lumber. Proper handling procedures are covered in standard drying texts, such as Drying Hardwood Lumber . (Note: Any lumber kiln dried at over 130 F will be sterilized.)
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