tree cookie

A tree cookie is a horizontal slice cut from a freshly felled log, typically 2 to 4 inches thick, which exposes the annual growth rings and internal structure of the wood. The slice is then allowed to air-dry or is treated with a preservative sealant, creating a durable artifact that retains visible detail of the tree's life history.

The term originates from the informal resemblance of a thin, circular disk to a cookie, though the actual thickness depends on the tree diameter and intended use. A tree cookie from a 30-inch diameter log might weigh 15 to 25 pounds when freshly cut; smaller disks from saplings may weigh only a few pounds. The exposed surface is often sanded smooth to improve visibility of the ring structure.

Tree cookies serve several practical purposes in forestry and education. Foresters and timber cruisers use them to estimate tree age by counting rings, though accuracy depends on ring width and species. Wet storage or improper drying causes checking, warping, and fungal discoloration that degrades the specimen. End-grain sealing with polyurethane, wax, or commercial wood sealers slows radial cracking, which is the most common preservation problem.

Variants and wider use

Large cookies from old-growth trees become archival records, sometimes displaying 200 to 400 rings. Sawmills occasionally produce cookies as byproducts and donate them to schools and museums. The slice must be cut before the log seasons; once wood has kiln-dried, sawing produces dust and does not reveal rings with the same clarity. Cookies from softwoods like pine and fir are easier to dry uniformly than those from dense hardwoods.

In timber appraisal, a tree cookie provides evidence of growth rate and climatic history relevant to wood quality assessment, though modern increment boring and core sampling are now the standard methods for non-destructive measurement. The term is regional and informal; it does not appear in official forestry standards or grading systems.