Oct 27, 2022 - Science

The push to protect ancient trees — and the knowledge they contain

Illustration of trees in a bell jar

Illustration: Gabriella Turrisi/Axios

Ancient trees contain unique information about Earth's past — the planet's climate, the ebb and flow of civilizations, and the biology of a species' survival — that can be valuable for modeling the planet's future.

  • As these trees are threatened by people, pests and fire, scientists and historians are increasing calls for their protection.

Why it matters: Ancient trees and the records they carry can't be restored.

  • "If we lose them, they are gone," says Chuck Cannon, director of the Center for Tree Science at the Morton Arboretum.
  • "It is a type of extinction. We lose our connections to past conditions and potential ways in which a forest or tree species can evolve."

Details: Ancient trees are those that are unusually old for their species — "often more than 10 to 20 times older than the average tree in the forest," Cannon and his colleagues wrote in an article published last week in the journal Trends in Ecology and Evolution.

  • Some can live for centuries. An estimated 25 species, including baobabs (Adansonia digitata) and bristlecone pines (Pinus longaeva), can live for at least 1,000 years without human help

That's the scientific definition. But ancient trees are also part of what historian Jared Farmer calls elderflora — long-living trees venerated by cultures and even "honored with personhood," he writes in his new book, "Elderflora: A Modern History of Ancient Trees."

  • Farmer, a professor at the University of Pennsylvania, chronicles how trees got caught up in conflict, industrial revolutions and science, and how they've been protected, prodded and pillaged along the way.
  • He also traces the birth of tree ring science, or dendrochronology, and the contributions and concerns it raised.

How it works: Old trees support other species of plants and animals, form networks of roots that carry nutrients beneath the forest floor, and influence their own microclimates.

  • They capture carbon from the air. Trees grow faster later in their life — and bigger trees store more carbon.
  • Their rings carry proxy data about temperature, precipitation and disturbances in past climates — information that can help predict how a forest might respond to changes in temperature and other conditions in the future or to model climates to come.
  • The unique combination of genetic and epigenetic changes in these "lottery winners," which survive for centuries or more, helps forests adapt and survive, Cannon and his colleagues reported earlier this year in Nature Plants.
  • "There is no reason a tree should die from old age — they are always renewing their organs. It is actually a very rare event, almost chance," Cannon says. Other scientists are researching that theory.

"Old trees have seen a thing or two," says Brendan Buckley, a professor at the Tree Ring Lab at the Lamont-Doherty Earth Observatory of Columbia University (LDEO), who studies the tree rings of tropical trees to reconstruct past droughts, monsoons and other events.

  • And tree rings are "so much more" than data, he says. "There's this real move lately to understand much better how trees actually grow" and "what's gone into making" the tree rings that give scientists the ability to reconstruct past climates.

Farmer coins two terms that he says he hopes scientists will pick up and define for their work.

  • Perdurables: There are annuals, biennials and perennials, but Farmer proposes the term "perdurables" to define the life forms that live for more than 1,000 years.
  • Chronodiversity: Similar to measures of biodiversity, Farmer suggests this term to capture the diversity of the ages of trees in a forest, the ages of species, and the range of ages humans can experience in the natural world.

Where it stands: Longer warm seasons and air fertilized with CO2 from climate change are spurring the growth of temperate and boreal forests.

  • But forests are skewing young — between 1900 and 2015, one-third of the world's old-growth forests were lost, according to a 2020 study.

What to watch: The Biden administration earlier this year issued an executive order directing the creation of an inventory of old-growth forests and their conservation.

  • Cannon and his colleagues are calling for the framework of the Convention on Biological Diversity to include mapping and monitoring old-growth forests and ancient trees. This would include working with Indigenous people and remote communities to better understand ancient trees.
  • But ancient trees aren't necessarily in old-growth forests. They can be scattered around and don't always stand out, making their protection challenging, Cannon says.
  • Cannon is a proponent of propagating and cultivating ancient trees, but he says there is also more research needed about conservation horticulture.

The big picture: Farmer, as a historian, views long-lived trees — and the stories of and in them — as a a way to think long-term.

  • "To me, the proper understanding of humans' place on the planet acknowledges not just the precedence of Earth for humanity, but the precedence on Earth of so many other kinds of life forms [that] have successfully adapted to a changing planet over a timescale that is barely within our realm of understanding," he says.
  • "Could we learn to live on the planet a fraction of the time that some of these ancient conifers have? That's a great species-level goal, right?
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