In their own way, trees can see, smell, taste, feel and hear. In the wild, most trees live in communities and even have families. To reveal the hidden life of trees, my guest this week is forester and New York Times bestselling author Peter Wohlleben.
Peter’s most recent book is “The Heartbeat of Trees: Embracing Our Ancient Bond with Forests and Nature.” He has loved nature his whole life, and as a child, he wanted to be a conservationist. Because of his appreciation for trees, he became a forester with the German Forest Commission. However, he realized in time that being a forester did not mean caring for trees in the way he had envisioned. He found that the foresters he encountered were like butchers who don’t have a sense of animals’ feelings. He sought a better way.
Peter realized that many German forestry students and even politicians believe that if foresters do not thin trees with chainsaws and then re-plant, a forest will die. But he rejected the idea that forest management is necessary. He points to the Amazon rainforest, which thrives with no human intervention.
One of Peter’s first jobs as a forester was to fell old beech trees. He says it’s fascinating to see a tree falling down, but also noisy and sad. Lay people instinctively know that it is not OK, he says, while foresters were trained to believe that felling old trees is important for the environment. Foresters are taught that younger forests are better and more productive.
“As a trained forester, I thought, ‘Yeah, that’s how it has to be,’” he recalls. “But I felt sorry for the old trees.”
Peter began to travel around in search of alternatives. He found forests that were managed in a more environmentally friendly way, and he began talking to scientists. After 30 years of travels, he visited a virgin forest in Europe, a beech forest in Romania. The forest was exactly as it should be, he says.
When Peter was tasked with managing a forest, he did it in a truly environmentally friendly way — even though he didn’t have permission to work that way. When his boss told him to cut down old beech trees, he always said he would do so “next year,” and he kept that up for 10 or 20 years. He finally quit and created his own timber business that was outside of the state forest commission. With the freedom to apply his own discretion, he created protected areas in an old beech forest.
Publishing ‘The Hidden Life of Trees’
No longer a member of the state forest commission, Peter was also free to write books about what was really going on. His most famous and most successful book is 2015’s “Das geheime Leben der Bäume,” which was translated into English and published as “The Hidden Life of Trees: What They Feel, How They Communicate – Discoveries from a Secret World.”
A good theme running through the book is the sociality of the trees. As explained in the book jacket, “The Hidden Life of Trees” draws on groundbreaking scientific discoveries that describe how trees are like human families: Tree parents live together with their children, communicate with them, support them as they grow, share nutrients with those who are sick or struggling and even warn each other on impending dangers.
His German publisher’s original print run of the book was just 3,000 copies. The popularity of the book was grossly underestimated. Today, 2 million copies have been sold worldwide, and it has been adapted into a documentary.
To build on the success of the book, Peter’s son suggested he start his own forest academy. Now, he’s living his childhood dream: “I’m a tree keeper,” he says.
In the documentary, Peter visits the oldest living tree in the world, which is almost 10,000 years old. The same scientist who discovered that tree tested another 20 trees that he found were more than 8,000 years old.
Peter’s guide on his journey to see the oldest tree was the most active environmentalist who protects old forests in Sweden. The environmentalist showed Peter how slow changes in an old-growth forest can be: A certain type of tiny lichen only appears on pines that grew to be 500 years old, suffered a wildfire, and then had 100 years to regrow. In Germany, where the oldest trees are only 300, this lichen can’t grow.
One of Peter’s most important observations is that old trees in managed forests tend to die, while old trees in unmanaged forests just keep on living.
Mother Trees and Tree Families
The Brothers Grimm, the 19th century German fairy tale writers, included in a dictionary the term “mother tree.”
“It’s a technical term from foresters,” Peter says. “Foresters knew for a century that mother trees are caring for their offspring and that there is a connection. Thinning a forest destroys those family bands, he explains. To justify thinning, people were taught that trees compete against each other for resources like water and canopy space. “Trees don’t need as much space as possible or water as possible,” Peter says. “They need their family, their forest ecosystem.”
Peter says trees don’t compete — they support each other. For example, when one tree is weak, the other trees support it by pumping sugar solution through the root system to keep the suffering tree stable. The roots don’t connect every tree in a forest to each other, but a fungi network does. The network moves sugar and also “news.” That means trees can spread the word that a disease or pest attack is underway. When the word spreads, other trees put up their defenses.
The fungi networks are made up of mycelium, the fungal threads in the soil below the fruiting bodies of mushrooms. Mycelium looks like a spongy, white mass of densely connected fibers. Peter says the fibers are so small that in one teaspoon of forest soil there are miles of fungal threads. He compares these to the fiber-optic cables of the internet.
Generally, trees use these networks to transport sugar between members of their own species. However, Peter says the fungi do not always follow the plan; they may share some sugar with a beech even though an oak intended it for another oak.
Trees in the shadow of a mother tree grow slowly because they receive less light, and they are healthier for it. Trees that grow with no mother tree don’t have the benefit of slow growth. They get full sun and grow fast, which is stressful. But there are “lone wolf” trees as well, such as beech and apple that enjoy big distances between each other.
How Forests Change the Climate
The German geographer and naturalist Alexander von Humboldt wrote in 1831 that big forest ecosystems can cool down the landscape and produce their own rain clouds. Today, we know that is accurate because of satellite data. A forest can cool the landscape by about 20 degrees on a hot summer day, Peter says.
Tree Senses and Communication
For humans, our survival strategy is to run away, Peter says, while trees must stand in one place for centuries. So trees have developed a different reaction for every danger.
When a tree is attacked by a bark beetle, there is a measurable electrical signal in the tree’s tissue, Peter notes. Then the surrounding trees, which are not yet affected by the bark beetle, start pumping poisonous substances into their bark and leaves as a natural defense to pests. But how do the unaffected trees know it’s time to put up their defenses? “The only conclusion is they have been warned,” Peter says.
In root tips are brain-like structures where trees make decisions in the moment. There is research happening right now about neurotransmitters in roots that are identical to what’s found in human brains, Peter points out. However, the roots lack neurons, so the trees must rely on chemical signals that travel slowly from cell to cell.
A much faster form of communication between trees works by smell. The trees can release gas from their leaves, and with just a little wind the other trees will receive the signal.
Peter says not only can trees smell, but they can also taste the saliva of a caterpillar or deer munching on its leaves or branches. Researchers are experimenting with applying deer saliva to tree wounds to see if the trees react differently. One reaction researchers have observed in deer-browsed trees is they produce substances that upset deer’s stomachs.
Trees can even “see.” Peter says most plants can recognize more than just light and dark — they can detect if a neighboring plant is a member of the same species or same plant family. “We say, ‘that’s crazy,’ but that is the research, for example, from Switzerland,” he says. “They are not very humorous scientists.”
Peter explains that switching off certain genes, such as the genetic code for detecting blue and red wavelengths, proves that trees use sight. “When you switch it off, they don’t care for family members, and when you switch it on, they take care. They bring their leaves a little bit away so the neighboring plant — if it is a family member — gets more light.”
Tree roots can hear at a frequency of 200 hertz, the frequency of flowing water underground. Roots can also produce noise that other trees can pick up on. And, Peter says, trees can hear when insects munch on the leaves of neighboring plants, and they respond by pumping poisonous substances into their leaves.
Trees also have sleeping behavior, similar to how many flowers open in the daytime and close up at night. Trees allow their branches to hang a little lower at night even though the water pressure within them is rising. Why trees do this, researchers don’t know.
Though “sleep” in trees is not well understood, we do know that it is necessary for their long-term survival. Trees that grow near a streetlight don’t live to be old because they don’t get that nightly rest.
How Trees Manage Seed Output to Reproduce Successfully
When trees produce more seeds than normal, people often think they are doing so for the benefit of animals, Peter says. The idea goes that if oak trees produce many acorns or beech trees produce many nuts, it’s going to be a harsh winter. But trees don’t like having their seeds eaten by animals.
Trees arrange to all bloom at the same time and set seed at the same time so there is a big amount of seeds all at once — typically more than the animals will be able to eat. Some seeds will be able to survive and grow into trees.
When trees produce far more seeds than average, this is known as a mast year. The following year, the production of seeds drops significantly, and there is not enough food to go around for the animals. That reduces the animal population.
It’s been calculated that a mother beech tree must produce as many as 2 million seeds in order for just one seedling to survive and become a mature tree. All those other seeds and seedlings are victims of disease or drought or they get eaten.
The Best Way to Restore a Forest
Peter does not believe that planting seedlings is the best way to restore a forest. He recommends letting nature take its course.
Seeds make better trees than transplanted seedlings because those transplants had their roots pruned, Peter explains. Without their root tips — their brain structures — the transplants struggle to become established. The root system will regenerate but not to its original quality. Transplants generally are shallow rooted and therefore have less access to water and are more susceptible to falling in storms.
Seeds from poplar and birch trees will travel great distances — up to 100 miles — to sprout in suitable areas, Peter says. A seed-planted tree grows such a great root system that it can quickly surpass the growth of a seedling-planted tree.
The Future of Forestry
The forestry industry is huge and not going away. So will our children and grandchildren get to see old-growth forests with trees that are hundreds of years old? Peter believes they will have those trees, but he also thinks we won’t know when the tipping point is until it is too late. “We are in the wrong direction, and we should stop now and go back,” he says. “The longer we are driving in the wrong direction, the way back will be longer.”
When we step back, we will see forests re-establish and re-wild themselves, Peter says. He notes that climate change is a challenge for trees as well, though it’s a bigger problem for single trees than forests, which regulate their own climate.
We need to close power plants that burn timber on a large scale, Peter says. But the best way to protect forests is to get out into one and enjoy it. “Take your time, especially with children,” he recommends.
Next on Peter’s agenda is writing a book on forestry for his forestry academy. He will teach forestry in the way that he originally envisioned it to be. He and scientists are visiting a monastery to write the book with the benefit of silence and no distractions.
I hope you have a greater understanding of the complicated life of trees after hearing my conversation with Peter Wohlleben. If you haven’t listened yet, you can do so now by clicking the Play button on the green bar near the top of this post.
How old was the oldest tree you visited? Let us know in the comments below.
Links & Resources
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“The Heartbeat of Trees: Embracing Our Ancient Bond with Forests and Nature” by Peter Wohlleben
“The Hidden Life of Trees” documentary
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