Do Trees Die of Old Age?

Do Trees Die of Old Age?
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The oldest known tree in the world is an unnamed Great Basin bristlecone pine in the White Mountains of California. At 5,064 years old, this tree has seen things, man. Though not even remotely as majestic or gigantic as the mighty Redwoods, the bristlecone pines, which claim the top three spots on the list of the world's oldest trees, look the part of their ancient age: round, wise, and a little scraggly around the edges, like crotchety old grandmothers.

So will there come a time when these sage trees die from old age?

Honestly, the question is a bit misleading. No living thing, whether plant or animal, really dies of old age. When we say that a human dies of old age, it means that he or she passed away from one of the common diseases associated with aging, like pneumonia, influenza, cancer, or liver failure. Dying from old age is not actually a scientifically recognized cause of death, there's always something more specific.

When animals senesce, or grow older, their cells may cease to divide, or the division process may grow increasingly sloppy, leading to deleterious mistakes. On the outside, this aging process shows through cognitive decline, or wrinkles in humans. One animal in particular, the hydra, actually doesn't seem to senesce. For all intents and purposes, it is biologically immortal.

While it's not precisely known whether or not individual trees are biologically immortal in the same fashion, they definitely don't grow old the same way animals do. Trees grow indeterminately, meaning that with the right conditions, they can grow and grow and grow, with only the laws of physics limiting their height. (There's a certain point where a tree cannot send enough water from the roots to the top layer of leaves, preventing adequate photosynthesis.) Amazingly, once they hit that maximum height, instead of growing taller, they grow wider! And they do so at an ever-increasing rate! That's right, trees actually grow faster as they age. Scientists reported this amazing finding in the journal Nature earlier this year, after examining the growth of over 700,000 trees worldwide.

While it's not yet known precisely why trees grow faster as they age, the secret to their perpetual growth has already been revealed. Most plant cells are perpetually embryonic, meaning they can change into another cell type at any time.

So if trees never stop growing, why is it that the oldest individual tree is just 5,064 years old? Why aren't there trees that are hundreds of thousands of years old, or even millions of years old? An enlightened Redditor stated the answer succintly:

The longer a tree is around the more opportunities it has to have something happen to it that leads to its death. This could be a lot of different things such as a storm, a disease, an insect infestation. Often a tree can survive numerous instances of potential death, but over time these instances can aggregate, or lead to a greater susceptibility to death. For example, a storm might knock off a tree limb, which might give the tree a higher risk of exposure to a disease....Or a tree might live for quite a long time, out growing trees in the area, making it more likely to be struck by lightning, or blown over in storm.

So a tree may not die of old age, but after a long enough time, simple statistics dictate that it will die of some other cause. Such is life.

(Images: AP, Dcrjsr

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