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You Can’t Judge a Tree by its Bark

April 15, 2010

Today is my birthday. I'm 40 years old, and I'm not happy about it.

Now I've always been told I have a youthful face so as I enter - gulp - middle age, I realize that I might be able to lie about my age and get away with it. Maybe shave just a few years off the top and linger around 38 for awhile.

And then I realize as I observe an oak I'm evaluating for a customer that a tree never has this option.

A tree's height and spread reach a maximum and then plateau - hiding actual age rather well. But a tree's trunk increases in diameter throughout its life telling the tale of age as if it were wearing the number on its metaphorical forehead. No sit ups can be done to whittle away its middle.

A tree trunk grows in diameter by adding new wood every year. Young trees may grow quickly, and may add about ½ inch in diameter each year, but slow upon maturity, growing approximately ¼ inch increments annually. Overmature trees reach a point where their diameter growth is one tenth of an inch for each year. So a tree with a 5-foot diameter measured at breast height might be about 180 years old.

Of course, like every rule there are exceptions. Some trees are fast growers, others slow and steady. Obviously, if you know when a tree was planted, you can easily and accurately determine its age. And for trees with only stumps remaining, you can count the rings to approximate years.

But how can you tell the age of a living tree?

Professional arborists can use an increment borer to count the rings on a trunk cross section and use the core to determine not just the age, but the structural condition of the tree.

Trees certainly have an advantage over us in their longevity. So if I'm feeling old at 40, I can't imagine how some of the oldest trees feel that are more than 70 times my age. The world's oldest individual tree lives 10,000 feet above sea level in California's Inyo National Forest. This tree, which is more than 4,700 years old, was about 100 years old when the first Egyptian pyramid was built.

Then there's the 3,500-year-old, 125-foot-tall giant bald cypress that lives in Florida's Big Tree Park. The height alone here shows its age - it's the biggest tree by volume east of the Mississippi River.

But size doesn't always show age. The General Sherman giant sequoia in California's Sequoia National Park is 275 feet tall and 103 feet around - the largest tree by volume in the world. But it's estimated to be between 2,300 and 2,700 years old, young compared to the previous two trees I mentioned.

And then, as I notice my body age, the great bristlecone pines make me feel really old. They don't seem to age like we do. At 3,000-plus years old, these trees continue to grow like their 100-year-old counterparts.

So I may not always feel as energetic as I did 20 years ago, but I'm still strong. Like these trees, I think I've aged gracefully. I'm certainly optimistic about it, and I think that adds an additional grace all its own.

Now if that grace could only do something about these wrinkles.

"Think you're a big fan of trees? We'd love to hear about it. Send your thoughts to Dave or Daphne at blog@davey.com ."

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