How do trees die?
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How and why do trees die? – Anish K., 11 years old, Boston, Massachusetts
Trees can die suddenly or very slowly.
Fire, floods or wind can cause trees to die quickly because the tree’s ability to transport water and nutrients up and down its trunk is severely impaired.
Sometimes a tree can die due to a severe insect infestation or disease. This type of death usually lasts from a few months to a few years. Again, a tree loses its ability to transport water and nutrients, but this happens gradually and more slowly.
A tree can also die of old age.
I am a scientist who studies trees and the web of life that surrounds them. The death of a tree is not quite what it seems, because it leads directly to new life.
Different trees, different lifespans
Trees can live incredibly long lives, depending on the species. Some bristlecone pines, for example, are among the oldest known trees, dating back over 4,000 years. Others, like lodgepole pines or poplars, have a much shorter lifespan, between 20 and 200 years. The largest trees in your neighborhood or town are probably somewhere in this range.
You’ve probably noticed that different creatures have different lifespans – a hamster generally won’t live as long as a cat, which in turn won’t live as long as a human. Trees are no different. Their lifespan is determined by their DNA, which you can think of as the operating system embedded in their genes. Trees that are programmed to grow very quickly are less strong – and have shorter lifespans – than trees that grow very slowly.
But even a sturdy old tree will eventually die. Years of damage from insects and microscopic creatures, as well as weather conditions, slowly end its life. The dying process may begin with a single branch, but eventually spreads to the entire tree. It may take a while for an observer to realize that a tree has finally died.
You might think that death is a passive process. But in trees it is surprisingly active.
The underground network
Roots not only serve to anchor a tree in the ground, they are also the place where microscopic fungi take hold and act like a second root system for the tree.
Fungi form long, gossamer threads called hyphae. Fungal hyphae can reach much further than the roots of a tree. They collect nutrients from the soil that a tree needs. In return, the tree rewards the fungi with sugars that it makes from sunlight in a process known as photosynthesis.
You may have heard that fungi can also transfer nutrients from one tree to another. This is a topic that scientists are still working on. Some trees are probably connected to other trees by a complex underground fungal network, sometimes called the “wood wide web.”
How the wood web works in a forest is not yet fully understood, but scientists know that the fungi that form these networks are important for the health of the trees.
Life after the death of a tree
Before a dead tree falls, it can stand for many years and provide a safe home for bees, squirrels, owls and many other animals. When it falls and becomes a log, it can provide shelter for other creatures such as badgers, moles and reptiles.
Tree trunks also host another type of fungi and bacteria called decomposers. These tiny organisms help break down large dead trees to the point where you can’t even tell they existed. Depending on conditions, this process can take a few years to a century or more. As wood decomposes, its nutrients return to the soil and become available to other living things, including nearby trees and fungal populations.
A tree leaves behind a legacy. While it lives, it provides shade, is home to many animals, and is a lifeline for fungi and other trees. When it dies, it continues to play an important role, giving rise to new trees ready to take its place, providing shelter for another group of animals, and ultimately providing food for the next generation of living things.
It’s almost as if a tree never really dies, but simply passes its life on to others.
Editor’s note: This story has been updated to highlight that much is still unknown about the relationship between trees and fungi.
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This article was adapted from The Conversation, a nonprofit, independent news organization that brings you facts and trusted analysis to help you make sense of our complex world. It was written by: Camille Stevens-Rumann, Colorado State University
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Camille Stevens-Rumann does not work for, consult for, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond her academic employment.
