Wood as a Building Material - Carpenter's and Builder's Math, Plans, and Specifications - page 57

the annual rings (see Figure 2-10). A wind shake may extend for
a considerable distance up the trunk. Other explanations for wind
shakes are expansion of the sapwood and wrenching from high wind
(hence the name). Brown ash is especially susceptible to wind shake.
Wind shakes cause cup checks in lumber (see Figure 2-11A). A star
shake resembles a wind shake but differs from it in that the crack
extends across the center of the trunk without any appearance of
decay at that point; it is larger at the outside of the tree. Heart and
star shakes cause splits in lumber (see Figure 2-11B).
(A) CUP CHECKS
(B) END SPLIT
Figure 2-11 Lumber defects caused by defects in the log. (A)
Cup checks are caused by wind shakes. (B) End splits are caused
by star and heart shakes. (Courtesy Practical Restoration Reports)
Figure 2-12 shows some common causes of black or loose
knots. Figures 2-13 and 2-14 show some results of improper drying
practices.
Decay of Wood
Decay of lumber is the result of one cause and one cause only: the
work of certain low-order plants called fungi . All of these organisms
require water, air, and temperatures well above freezing to live, grow,
and multiply. Consequently, wood that is kept dry, or that is dried
quickly after wetting, will not decay.