Trees do not pay taxes. Some seem to avoid death too. Many of the world’s oldest organisms are trees, including a 3,600-year-old cypress in Chile and a sacred fig in Sri Lanka that was planted in the 3rd century BC. C. A bristle pine known as Methuselah has been alive for nearly five millennia, standing in a forest in what is now called California.
But according to an article published Monday in Trends in Plant Science magazine, time devastates us all in the end. The document, “Long-lived trees are not immortal,” argues that even the most venerable trees have physiological limits, although we, with our insignificant lives, can never know.
Sergi Munné-Bosch, a plant biologist at the University of Barcelona, wrote the article in response to a January study on ginkgo trees, which can live for more than a thousand years. The study found that 600-year-old ginkgos are as reproductive and photosynthetically vigorous as their 20-year-old peers. Genetic analysis of the trees’ vascular cambium, a thin layer of cells just below the bark and creating new living tissue, showed no “evidence of senescence” or cell death, the authors wrote.
Dr. Munné-Bosch said he found the document “very interesting,” but disagreed with how some readers of the study in popular media and beyond had interpreted it.
“At least in my opinion, there is no immortality,” he said.
Those tree species that can live for centuries or millennia have many tricks for staying young. They have simple body plans and are developed in a modular way, so they can replace the missing parts. They are also based on their own dead tissue, which provides support and volume at a low metabolic cost. The trunk of a very old tree could be 95 percent dead, said Dr. Munné-Bosch, a strategy also used by other plants.
For these reasons, such a tree is much more likely to die from external causes than those related to age. In some populations, this can result in “negative senescence,” a phenomenon in which the durability of older trees means that they actually have a greater chance of survival than younger ones, Dr. Munné-Bosch said.
Still, “everything seems to indicate” that individual trees are deadly, he said.
But others have a different opinion.
“A modular organism like a tree could hypothetically live forever,” said Peter Brown, a forestry scientist who runs an ancient tree database called OldList. “I don’t think there is any real anatomical or physiological limitation to them not going ahead.”
However, in practice, “something always pops up” and disrupts either a windstorm, a wood harvester, or a swarm of bark beetles, he said. Dr. Brown said that many trees in OldList won the placement lottery: they are rooted in rocks, difficult to reach with an ax, and far enough from other trees that pests cannot spread.
Dr. Munné-Bosch points out some potential limits. For example, the vascular tissue that ginkgos produce becomes thinner every year. At some point, it could become too thin to function, killing the tree, he said.
Ginkgos also experience more physiological stress over time, along with a reduced supply of growth hormone. Despite their miraculous vascular cambiums, “even ginkgo trees are likely to die from ‘natural causes,'” said Richard Dixon, one of the authors of the January ginkgo article.
Dr. Brown and Dr. Munné-Bosch agree that the question is almost impossible to answer experimentally. Very old trees are rare, and the same tricks that enable their long-term survival make them hard to find. (The oldest group in the ginkgo study contained only three trees, all less than 700 years old.) Therefore, it is difficult to design a comprehensive study of them.
Furthermore, our own life is simply too short. Even if a scientist dedicated his entire career to very old trees, he could follow his research subjects for only a small percentage of their lives. And a long enough multigenerational study could see its own methods become obsolete.
For these reasons, Dr. Munné-Bosch thinks that “we will never test” whether long-lived trees experience senescence, he said. So in his own experimental work, he now focuses on bushes with more manageable lives, around 30 years old.
“I think in the end,” he said, “we have to accept that we will all die.”
