Shake, pith, red heart and other log-end features

The log end is the main information point in the yard. Eccentricity, rot, shake, resin and pith position are visible there. This lesson covers features that decide whether part of a log is usable.

Pith and boxed heart

The pith is the soft central core, surrounded by juvenile wood. Boards containing it ("boxed heart") are generally described as having tight, high-angle rings, higher longitudinal shrinkage and a tendency to crack radially in drying. Juvenile wood is defined by one university source as the first 10 to 15 growth rings. Many specifications limit or exclude pith for this reason; the cracking behaviour is general trade knowledge, not tested in the portal's sources.

Shake

Shake is a separation along the grain. Ring shake follows the growth rings and looks like a partial or complete circle on a log end. Star shake runs radially from the pith. Shake sometimes shows only after sawing or drying.

For oak in Great Britain (Price, 2015, Europe) the evidence is as follows:

• Star shake is the more frequent type.
• Ring shake is correlated with a sudden change in growth rate. Tentative data link it to sandier soils; low calcium and severe cold are also reported.
• The roles of wind and steep ground are not verified or proven in the source.
• About 21 percent of British high forest oak trees were estimated to be affected (Mather and Savill, 1994, as cited by Price).
• One highly shake-prone site had 73 percent of trees affected and a likely financial loss of about 21 percent on the overall sale parcel. The 21 percent here is financial loss, a different quantity from the 21 percent of trees affected.

These are British oak numbers and must not be transferred to conifers. The Oak species note adds that shake and heart defects are not visible on a sawn face until the board is cut, so end inspection of logs and careful opening cuts pay off (portal inference). Shaken logs are in practice downgraded or sorted into low-value products.

Worked example: how many shaken trees to expect?

A buyer is offered 250 oak logs from British high forest. If the national estimate applied, about 250 x 0.21 = 52.5, so roughly 52 or 53 logs, would come from shake-affected trees. If instead the lot came from a site like the highly shake-prone one, the expected number would be 250 x 0.73 = 182.5, so about 182 or 183. The two answers differ by a factor of about 3.5, which is why you ask where the logs grew. The calculation is a planning illustration: a tree being affected does not mean every log cut from it is shaken.

Red heart in beech

Red heart (false heartwood) is a brown-red core that appears in some beech trees. It forms when oxygen reaches the stem centre in older trees. What the sources support:

• An EU project summary says beech loses market value when discoloured by red heartwood, mainly for aesthetic reasons, and that colour heterogeneity is the main barrier to selling red-heart furniture.
• A forestry study (Racko and co-authors, 2011) reported that crown shaping affected the size of the dehydrated zone and how often red heart occurred; a large crown on crop trees reached target diameter with low likelihood of red heart.
• Red heart is reported to contain more tyloses, which slow drying.

The frequency of red heart and the price discount were not verified by the portal, so no percentages are given. Practical consequences: sort logs for red heart at the yard and plan sawing by end use. Using red-heart boards where colour does not matter is a portal inference, not a quoted recommendation.

Checklist: inspecting a log end

• Pith position and eccentricity: reaction wood or juvenile core?
• Circles or radial cracks: ring or star shake?
• Colour in the core: red heart (beech), discolouration, rot?
• Resin, stain or rot at the surface?
• Species and origin: do the shake or red-heart numbers you know even apply?

Key points

• Shake is a separation along the grain: ring shake follows the rings, star shake runs from the pith; it may show only after sawing.
• In British oak about 21 percent of trees were estimated to have shake, and one site had 73 percent; do not transfer to conifers.
• Red heart in beech is a colour defect that reduces market value for appearance uses; frequencies were not verified.