UNDERSTANDING OAK

Ross Roepke

 I have recently spent several sessions pulling small oak sprouts out of my gardens where they have come up in solid masses.  Last fall I raked up over 200 gallons of acorns from under two large white oak trees in my yard. 

 I understand that oaks don’t yield acorns until 50 years old.  Over the past several years the two trees have become more of a problem because of the seed pods and stain droppings in the spring, acorns in the fall, and the seedlings again the next spring.  Since the trees are native and pre-existing at the site and are so beneficial to our lifestyle, we have learned to tolerate their bad habits.

The woods of oaks can be divided into three major groups based on their structure: red, white, and live oaks.  Botanically, the tree species are separated based on their flower, leaf and acorn characteristics.

There are 58 U.S. species of oaks, some 30 exist in Tennessee, only about 20 are commercially important.  Of these twenty, eight are designated by the U.S. Forest service as “select” based on volume available, form of the tree, and quality of the wood.  These include Cherrybark, Upland Red, Shumard, Bur, Chinkapin, Swamp White, Swamp Chestnut, and White. 

Oak is a hard, heavy, coarse textured, stiff and strong wood.  With some exceptions, fast-grown oak with wide growth rings is generally stronger and heavier than the very slow-grown oak with very narrow growth rings.  This is quite contrary to common expectations. One of the anatomical differences between red and white oak that affects its drying is the presence of tyloses in white oak.  Tyloses are sac-like inclusions in the pores.  These increase the drying times of white vs. red oak lumber. 

The specific gravity for the two is respectively .60 and .56, on average; variations may be up to 10%.  The average green moisture content of the woods is from 70 to 85%.  Oak in one of the most difficult woods to dry.  Much of the drying damage is insidious, hidden in the material until uncovered during the milling.  Air-drying is still a preferred method for lowering the moisture content prior to kiln drying.  Drying sheds are recommended because of wood staining. Types of damage to look for in oak lumber include: surface checks, end checks, internal checks, warp, gray stain, brown blotches, case hardening, and longitudinal stresses/warping.  Many of these are causes by improper or rushed drying procedures.

Oak furniture became popularized early in the last century by the Craftsman, or Craft, or Stickley style.  It was made predominately of quarter-sawn oak that emphasized the apparent flakes in the surfaces of the wood.  There is a bit of return to the Craft style furniture today.  The quarter-sawn oak has become quite expensive, however.  Oak remains a popular wood for furniture in Tennessee because of its relatively low cost and sound characteristics.

 Ross Roepke, April 2003