Immortal Trees by Jill Mountain
1) Some of the earth's oldest living organisms are trees. For example, in California there is a bristlecone pine that is estimated to be over five thousand years old. An olive tree called "The Sisters" in Lebanon is estimated to be between six and seven thousand years old. What causes some individual trees in a species to live for so long? Scientists have studied some of these Ancient trees, hoping to find a clue that might help extend human life.
2) Professor Howard Thomas of London's Imperial College has determined that aging in plants is a response to environmental stress. In most cases, after a number of years, trees simply lose the battle with the elements, pests, and environmental pollutants, and simply die. Plants already have an advantage as their stem cells, or the cells that define every other cell in their structure, remain intact and accessible longer. In some plants, original and intact DNA remains within stem cells in the root system long into the organism's life. The advantage of this is that as exposed parts of the plant are damaged or destroyed, the original DNA is available to create new cells and rejuvenate the plant quickly.
3) Another advantage that some plants have, which may explain why these ancient trees are still around is dormancy. Some living things are able to temporarily shut down their metabolic activity. For example, some animals hibernate in the winter. They don't consume food, they don't move, they simply rest in a sort of deep sleep for several months. Similarly some trees shed their leaves in the fall and go into a form of dormancy for the winter. These dormant phases slow down the biological clocks, and things do not age when they are dormant.
4) However, this theory of dormancy does not apply to all ancient trees. One of the world's oldest trees, the Olive Tree of Vouves, is 2000 years old, and does not lose its leaves in the fall. It is an evergreen tree, which means it holds its leaves year round. Olive trees grow very slowly, which may explain the Olive Tree of Vouves' longevity. Its natural biological clock is slow, and although it does not become dormant, the tree does not grow any more quickly than most deciduous trees.
5) Ultimately, Dr. Thomas has determined that the process of aging affects all living things in similar ways: cells are destroyed and the replacement of those cells eventually slows and stops. When dead or damaged cells are no longer replaced, the organism cannot survive. However, all organisms do not undergo the aging process at the same rate. The rate of growth of an organism seems to have a direct correlation to the lifespan. Compare, for example, a puppy that grows from birth to adulthood in just one or two years, to a human who may continue to grow for seventeen or eighteen years. The human takes a longer time to reach adulthood, but also has a much longer lifespan than the puppy. Similarly, a slow-growing tree, or a tree that becomes dormant for part of the year grows to maturity much more slowly than a human, and, thus, will have a much longer lifespan.