Two varieties of bristlecone pine trees grow in the western United States. One, Pinus aristata, is known as the Rocky Mountain bristlecone pine and lives in Colorado, Arizona and New Mexico in U.S. Department of Agriculture plant hardiness zones 4 to 8. The other, Pinus longaeva, or the intermountain bristlecone pine, grows farther west, in Nevada, Utah and California in zones 5 to 8. The oldest bristlecone pines live in California's White Mountains, and among these are some of the earth's oldest living organisms. They live for thousands of years.
Trees that count their lifespans in thousands of years inhabit almost every continent. The Llangernyw Yew (Taxus baccata), which grows in a churchyard in North Wales, is probably 4,000 years old, while the oldest specimen of Patagonian cypress (Fitzroya cupressoides), which grows in the Andes mountains, is over 3,600 years old. Experts believe the Methuselah pine, the oldest bristlecone pine, has been alive for 4,600 years. The only other tree in the world to claim that kind of longevity is the Jomon Sugi, a specimen of a type of cedar tree native to Japan's Yakushima island. Opinions about its age vary; some believe it is 5,000 years old, others only 2,000.
The oldest bristlecone pines grow in isolated, arid regions of the White Mountains at elevations between 9,500 and 11,500 feet, which is just at the timberline. The soil they grow in isn't really soil, but dolomite and limestone -- substrates that cannot support other species. The growing season is short, and virtually all of the 12 inches or so of precipitation come from snow melt in the spring. The climate is forbidding. Even though there are few clouds to block the sun, temperatures are cold except for a few weeks during the summer, and high winds are frequent.
Because they have little competition for nutrients from the ground, bristlecone pines send out extensive root systems. There isn't much nutrition there, however, and because the growing season is so short, they grow very slowly. In some years, they fail to even add a growth ring, and they typically add no more than an inch of girth to their trunks every century. The slow growth of a bristlecone pine makes the wood very dense, and that is a survival advantage because it discourages insects. The trees remain small, with the largest specimens attaining heights of about 60 feet.
To survive in their hostile environment, bristlecone pines must conserve as much energy as possible. Their needles are as long-lasting as the trees themselves, remaining alive on the branches for up to 40 years. This saves the tree from having to put out new ones. Bristlecone pines survive years of drought or otherwise unfavorable conditions by going to sleep -- their periods of dormancy can last for years. Moreover, when a part of the root dies, the section of the tree above also dies, and the branches and bark fall off. The tree continues to survive, however, as long as even a minute section of bark remains.
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