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Talkin’ trees: Buds, whorls and rings

  • White pine branches whorl out from the center branch. Ruth Smith / For the Monitor

  • A bud and leaf scars on a hickory twig. Ruth Smith / For the Monitor


Friday, March 02, 2018

Recent warm weather has many people thinking about spring, but it will be a few more weeks before the tree buds begin to break open and usher in that season. In the meantime, take the opportunity to examine bare branches of trees and shrubs.

Each branch holds a collection of buds that were formed last summer. But not all buds are the same. Most are protected from cold and water loss by a covering of modified leaves called bud scales. Under the bud scales, depending on the species, there are miniature leaves and future stems, undeveloped flowers or a combination. Sometimes it’s obvious which treasure is hidden within as flower buds are usually rather plump. But in other cases you have to open and dissect the bud to determine its future, or wait for warm weather and watch it unfold. Try tying a colored string to a branch and visiting it regularly to observe this magical transformation.

When the buds open and new growth starts, a bud scale scar forms. By studying a branch, you can find these scars which resemble a bunched up turtleneck collar encircling the branch. The distance from the terminal bud at the tip of the branch, back to the first bud scar is the amount the branch grew in the past year. From that first bud scar back to the next is the growth from the previous year, and so forth. By counting back to the trunk you can determine how old a branch is.

Notice whether the terminal bud is singular or clustered. This will give you an indication to the branching pattern of the tree. Clustered buds, like those found on oaks, produce a candelabra of new growth, whereas the American beech with its single pointy bud shoots out a single straight branch. If you step back and examine the overall branching pattern of the tree you will see how that translates on the larger scale.

Be careful not to confuse the bud scars with the leaf scars on the branch. The latter are the places where former leaves were attached. They are often just below a current bud but do not go around the branch the way a bud scar does. It is interesting to scrutinize those leaf scars. They are distinctive in shape and pattern and can provide clues to identification of the species of plant you are observing.

If you observe evergreen trees, you will see similar clues which provide information about their growth. The terminal buds on trees such as pines, spruces and firs include a central bud surrounded by a whorl of side buds. Each of these becomes a new branch. The center bud grows upward as the leader or future trunk. The others spread out like spokes on a bicycle wheel, becoming the lateral branches. Therefore it is easy to distinguish the whorls of branches and the spaces between them. Each internode between whorls represents one year’s growth. Notice if some internodes are large and others are small. This tells the story of the tree’s growth pattern.

Determining tree ages using these methods is much less destructive than cutting them down and looking at growth rings. But if a tree has been cut for firewood or lumber, take the opportunity to observe its diary of growth, written in the concentric rings of its trunk as it expanded outward. Counting the rings is possible because of the different seasons of growth. In the spring and early summer rapid growth occurs creating large cells and light colored wood. Late summer growth is slower, the cells are smaller and closer together and the wood is darker. By the time fall growth stops, marking a clear line between each year (at least for trees in temperate zones). Therefore counting the dark rings (or the light rings) will provide an accurate tally of the age of the tree. As with the internodes on the pine, the size of the rings tells a story of the tree’s life. Wide rings represent good growth years, narrow ones indicate a drought, insect infestation or other stress.

Trees may not be able to speak to us, but with careful examination they can tell stories of the past. So go seek out a woodland storyteller and see what you can learn.