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Birdseye in Sugar Maple


The birdseye pattern in wood is much like maple sugaring and fall foliage. We're familiar with it, we value it, and we know a tremendous amount about it. And yet, ultimately, it remains a mystery. For the better part of a century, wood scientists have been beating up on each other's explanations of what causes it. Hell, there isn't even agreement on how to spell it. I've seen it written as the simple possessive, "bird's eye" and I've seen it written as the hyphenated possessive, "bird's-eye." But I prefer yet another common spelling, the one-word elegance of "birdseye."

Birdseye is a relatively rare kind of grain pattern or figure resulting from localized distortions in the growth rings. Imagine using a dull number two pencil to push through the bark and into the wood of a tree. If you and the pencil were strong enough, this action might distort the growth rings, resulting in small, conical indentations protruding from the inner bark into the tree across several growth rings of wood. On veneer and plain-sawn boards, such indented growth rings appear as tiny burl-like structures that resemble birds' eyes. The distribution of birdseye within the tree varies considerably. It may be found through the entire bole and even in branches or it may be restricted to one side of the stem or in irregular patches scattered throughout. Birdseye is most commonly found in sugar maple wood but a similar pattern has also been described in other species including red maple, yellow birch, white ash, and black walnut.

So, scientists seem to agree that birdseye figure results from these conical indentations which result from wood fibers actually growing in different directions. What remains a mystery is why they do so.

Birdpeck has always been among the most popular hypotheses attempting to explain the cause of birdseye. But many wood technologists have described how woodpecker or sapsucker wounds in live tissue usually heal over, whereas birdseyes actually continue to grow into the tree. Another common but equally insufficient explanation is that birdseyes result from little eruptions of formerly dormant buds within the tree, buds that inexplicably sprouted into rather than out of the tree. But, if birdseyes were born of such wayward buds, they would - like all stems and branches - contain a dark central pith and, you guessed it, birdseyes have no pith.

Several more obscure explanations have been suggested over the years - from fungi deactivating the cambium to suppression early in a tree's life to soil texture and fertility - but none has been fully substantiated. The mystery lives.

Fortunately, most of us can still sleep not knowing. For now, we're content observing birdseye wood and the trees it comes from and the sites they grow on. We think that if we can make enough careful observations, we might be able to predict from exterior features which trees contain birdseye figure. After all, if logs from such trees are otherwise salable, and they contain significant amounts of birdseye figure, they can be worth even more money.

For my own fascination with this process, I blame and thank David Paganelli, Orange County Forester in east central Vermont. He did what most good foresters do: he took me for a walk in the woods and he changed the way I look at trees. In this case, it was sugar maple trees. He was showing me a stand in which he had supervised a logging job and as we scouted around looking at standing trees and examining stumps and remaining parts of cut trees, we found evidence of a surprising number of birdseye maple trees. We looked at bark patterns and colors. We looked at stem shapes and sizes. We assessed stocking and composition. All the while we tried to findcorrelations with birdseye.

I don't think we ever agreed on bark features, but I sure do see what Dave means about that "coke-bottle" shape of the tree's lower bole. Paganelli showed me how unlike the flared bottom of a "normal" sugar maple tree, some birdseye stems have a particular constriction just above the root flare -- much like the constriction between the bottom and the middle of the old-fashioned coke bottles.

Although the coke-bottle test is not foolproof, it is preferable to more invasive and damaging methods of looking for birdseye. While our woods certainly don't need marauding bands of hatchet-wielding birdseye hunters hacking away at perfectly good trees, we could all benefit from paying attention to cut logs and observing how outer appearances translate into interior wood features. We just might solve a mystery.

Michael Snyder is the Chittenden County Forester in Vermont.