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  • The Life of a Tree

    You can tell a lot about a tree just by taking a closer look at the trunk.

  • For example, this 62-year old loblolly pine has quite the story hidden in its inner layers.

    But before we get into the story, let’s take a look at what makes up a tree trunk.

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  • The outer bark is the tree’s protection from the outside world.

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  • The inner bark, or phloem, is the pipeline through which food moves from the leaves to the rest of the tree.

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  • The cambium cell layer is the growing part of the trunk, producing new bark and new wood each year.

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  • The sapwood, or xylem, is where water moves from the roots up to the leaves.

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  • Heartwood, made of old xylem, is the central, supporting pillar of the tree.

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  • Each year, for 62 years, this tree has added a new ring of xylem cells to the trunk . . . nature’s way of marking the passage of time.

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  • If a slice of the tree could be viewed, it would look like this.

    Each ring in this tree cross section represents another year of growth.

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  • Every spring and summer, a tree adds new layers of wood to its trunk. The wood formed in spring grows fast and is lighter because it consists of large cells.

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  • In summer, growth is slower, forming smaller cells that produce darker wood. So, when the tree is cut, the layers appear as alternating rings of light and dark wood.

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  • You can tell how old the tree is by counting the dark rings, one for each year. And these rings tell us a lot about what has happened to the tree over the years.

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  • 62 years ago, a little loblolly pine sprouted when a seed fell out of a pine cone and became rooted in the soil.

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  • For 5 years this little tree grew, adding a new ring each year. The rings for each of these five years are nice and broad and evenly spaced. This tells us that the little tree enjoyed plenty of rainfall and sunshine.

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  • When the tree was 6 years old, something pushed against it, making it lean. You can see the rings on one side are now wider, as the tree built “reaction wood” to help support it.

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  • 10 years later, whatever was pushing against it was removed and the tree started to grow straight again. But its bigger neighbors were growing too, and their crowns and root systems took much of the water and sunshine. See how the newest rings are not as fat?

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  • After some years of competition, the surrounding trees had either fallen or been harvested. With the larger trees removed, there was once again plenty of rain and sunlight for the tree. The wider rings show the tree began growing rapidly again.

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  • A fire swept through the forest. Fortunately, the tree was only scarred.

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  • Year by year, the fire scar was covered by newly formed wood. In recent years, the newly formed rings became thin and c se together. This may have been caused by a prolonged dry spell. One or two dry summers would not have dried the ground enough to slow the tree’s growth this much.

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  • Fifteen years later, another series of narrow rings may have been caused by an insect like the larva of the sawfly. It eats the leaves and leafbuds of many kinds of coniferous trees.

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  • Tree rings offer us a glimpse into the past — a unique look at the life of a tree.

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