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The world's oldest living tree is a 4,767-year-old bristlecone pine. It resides in the White Mountains near the California-Nevada border. An average bristlecone pines lives for 1,000 years, with a few surviving to over 4,000 years. Alerce trees and sequoias also live well into their thousands. These ages are especially impressive given that urban trees live (on average) for only 32 years and inner-city trees for only 12. So what causes mature trees to die? Apparently, they run out of energy. As trees grow and
age, their size and complexity demands more energy. At the same time they're able to store less energy for emergencies. As a result, older trees are less able to respond to stress and eventually succumb to pollution, drought, insect infestation, or lack of nutrients. Urban environments are especially stressful. Bristlecone pines have a number of energy-conserving survival strategies that enable them to reserve the energy needed to survive long periods of stress. Trees don't die from "old age," but older trees eventually die from stress placed on their ability to produce energy. Species that successfully reserve energy and live in less stressful environments may live for thousands of years.
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