Sunday, December 5, 2010

Life Lines 68


I used to think the oldest tree was called Methuselah, growing somewhere on the eastern Sierra Madre range just before California abuts the Nevada border. It is a 4,647 years old bristle-cone pine (Pinus longaeva). When I saw it years ago in a National Geographic magazine, it looked weather-beaten, as indeed it had survived chilly winds and hard times at high altitude. The bristle-cone pines ousted the redwoods (Sequoia gigantea and Sequoia sempervirens) which I had earlier thought to be the oldest trees still living.

Now a new contender has emerged in Western Sweden, near the Norwegian border, high up in the mountains. It is a Norway spruce (Picea abies). The tree has grown and re-grown (from a sprouting of its roots) dozens of times, leaving behind, in the near tundra that has preserved its older remains, a record going back to 9,550 years. Swedish scientists sent specimens of cones and limbs from these diggings to Florida for carbon dating. They also did a DNA sequencing of the specimens from present trees and discovered that they shared a single genome. In colder weather the Norway spruce is stunted and looks like a bush about two feet tall. In warmer weather the bushes turn out to be trees that sprout like mushrooms. Over the past 9000 or so years, as earth cooled or warmed, the bush-tree cycle took place and as trees they shed their cones and occasional branches. Buried in the cold ground they were preserved and one layer heaped on another for millennia. The preserved tree rings will give a history of climate change over the past 9000 years in Scandinavia.

I still consider the Methuselah bristle-cone pine to be the oldest intact living tree. Cloning seems like a cheater’s way to lengthen life. There is genomic continuity, but the sapling coming out of the roots of a tree felled by lightening or a storm, in my mind is a new individual and at best, an identical twin of the dead tree that produced it. Cut that Norway spruce down and its tree rings at most will be about 600 years old. That’s a youth compared to the red wood tree trunk on display at the American Museum of Natural History in New York City. That felled redwood was also relatively young compared to the oldest bristle cone pines.

But as the oldest genome of all trees known to us, it does tell us that there is no built-in clock ticking away in the cells of the Norway spruce, dooming it to self-destruction, as there is in most animals and plants. I wonder too about the redwoods. When I was visiting the University of California at Santa Cruz about 40 years ago I was delighted to see the “fairy rings” of younger redwood trees growing around the periphery of cut down giant trees. These are clones, not from the roots, but the living outer layers of those felled trees. I don’t know if anyone has checked the fallen and buried cones and branches of redwoods to see if they rival the Norway spruce in genome longevity. It will also be interesting to study the mechanism that makes those Norway spruce cells so resistant to dying out.

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