Some trees have the ability to live for thousands of years. They can do this because they grow at a slower rate than animals and have meristems that can repair damage.
Hidden somewhere in the White Mountains of California is the oldest tree in the world. Methuselah, a Bristlecone pine tree, has witnessed 48 centuries pass by. It was a small seedling when the Great Pyramids of Egypt were being constructed. It grew alongside humanity and civilization, and if it had the ability to speak, it would probably have some valuable advice for all of us.
If we compare the age of this tree to the longest lifespan of a human—122 years—our lives seem insignificant in comparison.
What enables trees like the Bristlecone pine to live for thousands of years, while the maximum lifespan of animals is only a few hundred years? How do they defy mortality?
What Does Aging Mean For A Tree?
One could argue that Methuselah isn’t the oldest tree in the world. ‘Pando’, a single clonal organism made up of 75,000 quaking aspen trees, surpasses it by an astonishing 70,000 years. The individual trees themselves aren’t very old, but they are all connected by an ancient singular root system; each tree is part of a larger colony.
This complicates the discussion about aging. The definition of the word is influenced by cultural implications, making it important to define what aging means in this specific context.
A picture of a Bristlecone pine in California’s White mountains. (Photo Credit: IrinaK/Shutterstock)
For many of us, age is associated with wrinkles and physical decline. However, age doesn’t necessarily imply weakness. Many animals, especially insects and plants that die soon after reproducing, don’t appear to be aged, yet they are at the end of their lives. As time goes on, the environment gradually damages living cells, leading to senescence.
What Is Senescence?
Senescence is a more fitting term to describe age-related concerns like wrinkles or another layer of bark. Senescence is when cells cease dividing and growing without dying. Senescence can occur due to stress or DNA damage. When cells stop dividing, new tissue cannot be formed, making aging inevitable. When people discuss studying aging, they often mean studying senescence. The goal is to understand how to live longer, while also avoiding associated diseases and wrinkles!
This brings us to the inevitability of death. All forms of life will eventually die. While true immortality does not exist, there are some organisms that come very close to it. Pando is the closest we come to biological immortality. Other organisms, like Hydra and the immortal jellyfish Turritopsis dohrnii, also live for hundreds of years. They achieve this through stem cell regeneration and reverting back to an immature state, respectively. These mechanisms, observed in other animals as well, are not what give individual trees their longevity.
So, where does this leave trees like the Bristlecone pine? Without the ability to clone or transform back into a seed, how do these trees live to be so ancient?
1. Plant Growth is Slow
Slow and steady wins the race, but slow and steady can also survive the race. Animals tend to rush through life. Insects may live for only a few weeks, enough time to reproduce and then die. Humans have managed to live up to a maximum of 122 years, but the average life expectancy for humans is only 72 years (as of 2016), according to the WHO.
Pando, the oldest clonal tree system on Earth, is located in Utah, USA. (Photo Credit: J Zapell/Wikimedia Commons)
In one year, when most human babies start walking, a 40-year-old bristlecone seedling may have only grown 15 cm (5.9 inches) in height. By the age of 40, humans are already experiencing a mid-life crisis, but this type of tree doesn’t even go through a growth spurt during its teenage years. A study discovered that the shoots of an old pine tree grew at a similar rate to the shoots of younger pine trees.
Slow and steady indeed!
2. Plant Regeneration is Possible
We don’t often hear about it, but plants have stem cells just like humans. These small groups of cells, known as meristems, give plants the ability to grow and change their growth behavior effortlessly. There are meristematic cells for growth in the root tips, shoots, and girth of the plant.
Meristems
Meristem cell populations can divide or remain inactive depending on the environmental conditions. When conditions are favorable, such as well-watered soil and moderate weather, the plant will activate its meristematic cells and produce new branches. However, if conditions are dry, hot, or cold, these cells can go dormant until the plant has enough resources to resume growth.
Plant meristematic cells are the plant’s stem cells responsible for growth and repair. (Photo Credit: pancakenap420/Shutterstock)
Quiescent Center
Researchers at Ghent University discovered that a group of plant stem cells called the “quiescent center” act as a backup for the plant’s original DNA. These cells do not divide frequently and actually suppress their division. When a cell divides, there is a risk of mutations occurring in its DNA. The cells in the quiescent center, on the other hand, appear to respond to stress stimuli. Essentially, this group of cells may serve a protective function when the organism faces challenging conditions.
3. Plants Can Pause Growth in Unfavorable Conditions
This flexibility and adaptability enable plants to withstand difficult times better than any other animal species. The presence of meristems, particularly at the tips of both the roots and shoots, allows plants to adapt to their environment. Since they cannot move, plants are compelled to increase their surface area and cope with damage caused by predators and the environment. Throughout evolutionary development, this has led to a modular developmental model.
Animals in the post-embryo stage are fully developed. Most of them grow up and their body parts either enlarge or they undergo metamorphosis to become adults. On the other hand, plants have the ability to grow new branches and roots as needed, and they can also regenerate damaged ones. Plants can produce as many branches as required, within the limitations of physics. The same applies to the root system. According to Iowa State University, the root system of a tree can cover a surface area four to seven times larger than the crown or upper branches of the tree. This is especially significant when considering large and old trees.
In 2012, the United States Forest Service identified another tree that is even older than Methuselah. This new champion is estimated to be 5,062 years old. Despite their aged appearance, these trees hold valuable information about the Earth’s history and its potential future. Scientists are studying tree rings to gain insights into past climate change events and to understand how trees are adapting to the current environmental changes. Old trees, with their extensive root systems and canopy cover, play a crucial role in ecosystems.
While plants may not age in the same way as animals, there are some animals that exhibit peculiar aging patterns as well. They may appear wrinkled on the outside, but their cells remain youthful. These ancient trees offer us a wealth of knowledge about the world, making them an important part of Earth’s history. Therefore, they deserve our utmost respect and protection.