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Methuselah Tree  

Old one backlit Old as the hills, a bristlecone pine stands majestic on an exposed flank of California's White Mountains. Note: To protect its identity, neither this nor any other bristlecone shown in this article is the Methuselah Tree.
A Tree's Secret to Living Long
by Peter Tyson

It's hard enough to accept that a tree that was a seedling before the Egyptian Pyramids went up is still alive today, as is the case with the Methuselah Tree, a bristlecone pine more than 46 centuries old. But it's truly baffling to learn under what conditions it has accomplished this extraordinary feat.

Just ask Robert Mohlenbrock. A decade or so ago, Mohlenbrock, a professor of botany at Southern Illinois University at Carbondale, visited the Ancient Bristlecone Pine Forest, part of California's Inyo National Forest. "At the time I thought that any organism that lived longer than the norm had to have optimal conditions going for it," he wrote in Natural History (5/85). For plants, that would mean moderate temperature, shelter from extreme weather, and plenty of moisture and nutrients.

Mohlenbrock was in for a surprise.

"When I stood looking at Methuselah," he wrote, "I knew I had been wrong." Though it was then midsummer, a bone-numbing wind tore right through him, Mohlenbrock recalled, and the scarce patches of soil at the roughly 10,000-foot elevation where Methuselah and other venerable bristlecones grow, appeared to contain little if any moisture. (A glance at the panoramas in Explore the Methuselah Grove will give you the idea.)

Old one in background How can bristlecones make it in such an unforgiving environment? Read on.

So what's Methuselah's secret? How can it and its kind survive, much less thrive, in conditions that would strike fear into the phloem of virtually all other plants? After decades of intense study, inaugurated in the 1950s by the legendary dendrochronologist Edmund Schulman, scientists are starting to get a grip on what makes bristlecone pines so Methuselah-like. (Or should we say "bristlecone-like?" After all, the biblical Methuselah, ancestor to Noah, was said to have lived 969 years, while the Methuselah Tree, thought to be the world's oldest living thing, has endured almost five times as long.)

It turns out that the bristlecone pine has evolved survival strategies that might make other, less hardy plants, well, green with envy. These strategies help it cope with one of the most flora-unfriendly environments on the planet.

Mountains of adversity
Bristlecone pines come in two varieties. Pinus aristata, the Rocky Mountain bristlecone pine, lives in Colorado, Arizona, and New Mexico, while P. longaeva, the intermountain bristlecone pine, occurs farther west in California, Nevada, and Utah. In California's White Mountains, the most ancient members of P. longaeva, including the Methuselah Tree, can be found high in the subalpine zone, from 9,500 feet to timberline at roughly 11,500 feet.

Young bristlecone Though appearing to be little more than a sapling, this bristlecone may be well over 100 years old.
Here, in the rain shadow of the mighty Sierra Nevadas, which block weather approaching from the west, the average annual precipitation is less than 12 inches, and most of that falls as snow in winter. In summer, which can provide as few as six weeks of warmth for bristlecone pines to generate growth and reserves for overwintering, precipitable moisture ranks among the lowest recorded anywhere on Earth. Moreover, the soil the bristlecones cling to is not dirt as most plants know it but dolomite, a limestone substrate with few nutrients. With so little time to get energy from the sun, and so little energy to be had from the soil, growth is grindingly slow. A bristlecone pine may add to its girth no more than an inch per century.

So how does the bristlecone make it in a place so hostile to life that the only other tree that can survive there is the bristlecone-like limber pine? A place that in certain areas hosts but a few forlorn clumps of that symbol of Western fortitude, the sagebrush, and in others looks like the rocky, lifeless surface of Mars?

Continue: A tree's tricks

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