The Wood

Individual trees are formed, shaped and scarred by the natural processes of growth, injury, death, and decay. Each piece of wood that I carve has unique qualities forged by these processes during its lifetime and subsequent decay.

STRUCTURE AND GROWTH

When the trunk (or limb) of a tree is cut, three layers are usually evident: the bark on the outside, the light-colored sapwood just inside the bark, and a darker layer of heartwood inside the sapwood. A single layer of cambium cells, essentially a vanishingly thin cylinder of cells just inside the bark, is responsible for the trunk’s annual increase in diameter. As each of these cells divides, it can produce a daughter cell to the outside, which becomes the innermost layer of the bark. Alternately, it can produce a daughter cell to the inside, which becomes the outermost layer of sapwood cells.

Sapwood is responsible for conducting water and minerals from the roots upward to the tree canopy. It is often an inch or more thick and is made up of light colored cells. The cells formed in the spring of the year are normally larger than those formed in the summer and fall, creating visible growth rings that can be counted to reveal the age of the tree or branch. As the cells of the older inner layers of sapwood die, they become heartwood, and in many species are infused with dark colored chemicals that inhibit decay. On Goat Hill, Ashe juniper has very decay resistant heartwood, the oaks are intermediate, and pecans and cedar elms have heartwood that is much more susceptible.

Certain parts of a tree can have particularly interesting and, when revealed, beautiful patterns of growth rings. For example, the anatomy of wood at the base of the trunk (where it meets the roots and which I call the core) is complex. The water conducting vessels of the root system must link seamlessly with those of the trunk, often forming beautiful swirling patterns of wood grain. In addition, multiple roots and sometimes multiple stems enter the core, creating attractive clusters of growth rings.

In long dead trees, decades of insect and fungal attack can convert the heartwood into a complex of insect tunnels and voids. Several sculptures in the Collection have been produced by simply carving away the softer material and polishing the remaining dark heartwood of the core with small rotary bits and fine sand paper.

*Detail of cedar bowl, made from the base of the tree. Multiple growth rings from its many roots and trunks are visible.*

*Detail of honey mesquite core sculpture, made from the extremely resistant heartwood at the base of the tree. Both stem and root bases are visible on its surface.*

*Detail of plateau live oak sculpture. The left and right halves are the remains of heart wood from the core where two large trunks that had grown together.*

Injuries to a tree can also alter growth patterns and affect the wood in interesting ways. A burl is a rounded knotty growth on a tree, usually formed by abnormal growth of wood around remnants of twigs or branches that had died or had not developed normally. This creates distinctive patterns in the surrounding grain. Several of the rounded sculptures in the Goat Hill Collection are made from burls and display the tortured grain of wood that grew around a dead branch. In some cases the original branch had rotted away, leaving a hole into the interior of the trunk. Such holes allow rainwater, insects, and fungi to enter the heartwood of the trunk, causing the heart to rot and often causing deposition of dark microbe-resistant chemicals around the wound.

One of my favorite bowls was made from a large burl on the side of a plateau live oak tree. A limb on the side of the trunk had died years before, and the sapwood of the trunk had responded by growing around it. With time, the center of the dead branch had rotted away, leaving an upward facing hole that the sapwood had never completely covered. When I began to cut the burl from the tree with a chainsaw, water gushed out. Rainwater had run down the side of the tree into the hole left by the decayed branch.

Plateau live oak burl sculpture, I cut this unique burl from the side of a very large, long-dead plateau live oak standing along Highway 36 just east of Hamilton, Texas- a tree that my grandmother played under as a young child, soon after her family moved to Hamilton in 1882. The burl was formed by reaction of the tree to the death of a large limb, which had long since rotted away.

*Bowl from plateau live oak burl. The outlines of the dead branch and the unhealed hole are visible in the background.*

DEATH AND DECAY

Wood decay, or rot, is caused by microorganisms, primarily by two classes of fungi: white rots and brown rots. White rots destroy all three major wood components (lignin, cellulose, and hemicellulose), eventually producing a fibrous, light-colored material that is structurally weak. However, in the early stages of white rot the wood remains strong enough to be carved. In contrast, brown rots break down cellulose and hemicellulose, leaving most of the soft brown lignin component intact. When carving affected wood, soft areas of brown rot can be easily removed to reveal underlying structures that have not yet been attacked by the fungus.

In general, live trees tend to decay from the inside out and dead trees from the outside in. “Sap rot” primarily develops in the sapwood of dead trees, even while they are still standing. White rot fungi can reduce sap wood to a soft fibrous mass that is easily removed, leaving the dark heartwood to be carved into decorative bowls or sculptures. “Heart rot” is often found in the center of living trunks and large limbs and is one of the principal reasons that large trees are often felled by wind storms. The most dramatic example of heart rot on Goat Hill was revealed when my father’s favorite tree fell unexpectedly in the fall of 2016. “Bob’s Tree,” as we called it, was a massive post oak over four feet in diameter. The void in its heart when it fell was over two feet in diameter at ground level and extended over ten feet up into the trunk.

Detail of plateau live oak sculpture. The base of this tree, bulldozed in the 1970s, had been almost completely consumed by rot when I discovered it in 2018. After removing the soft decayed wood, only the most resistant heartwood remained, encircling the void in what had been the center of the tree.

In some cases, rot can affect wood in unusual and beautiful ways. “Spalting”produces thin dark red, brown, or black lines that trace outline the areas infested by a particular fungus. The lines are typically formed during the early stages of decay before the fungus has substantially weakened the wood. Each line is impregnated with melanin and other waterproofing and antimicrobial metabolites, protecting the area it outlines from invasion by other fungi. I find that spalting is more frequent in hardwood trees with light-colored wood (like our pecans) than in our oaks and Ashe juniper.

Insects — and a tree’s reaction to their attacks — can also create interesting holes, tunnels, and patterns of discoloration in wood, often causing the tree to produce and impregnate surrounding areas with resins and other chemicals that resist fungal infection.