The Hidden Life of Trees

Peter Wohlleben, a German forester and author, has a rare understanding of the inner life of trees, and is able to describe it in accessible, evocative language. His book, The Hidden Life of Trees: What They Feel, How They Communicate, has sold more than two million copies worldwide. Wohlleben draws on groundbreaking scientific discoveries to 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 of impending dangers. Wohlleben also shares his deep love of woods and forests, explaining the amazing processes of life, death, and regeneration he has observed in his woodland.

 
A revolution has been taking place in the scientific understanding of trees, and Wohlleben is the first writer to convey its amazements to a general audience. The latest scientific studies, conducted at well-respected universities in Germany and around the world, confirm what he has long suspected from close observation in this forest: Trees are far more alert, social, sophisticated -- and even intelligent -- than we thought.

 
There is now a substantial body of scientific evidence that shows that trees of the same species are communal, and will often form alliances with trees of other species. Forest trees have evolved to live in cooperative, interdependent relationships, maintained by communication and a collective intelligence similar to an insect colony. These soaring columns of living wood draw the eye upward to their outspreading crowns, but the real action is taking place underground, just a few inches below our feet.
 

All the trees in a forest are connected to each other through underground fungal networks. Trees share water and nutrients through the networks, and also use them to communicate. They send distress signals about drought and disease, for example, or insect attacks, and other trees alter their behavior when they receive these messages. Scientists call these mycorrhizal networks. The fine, hairlike root tips of trees join together with microscopic fungal filaments to form the basic links of the network, which appears to operate as a symbiotic relationship between trees and fungi, or perhaps an economic exchange. As a kind of fee for services, the fungi consume about 30 percent of the sugar that trees photosynthesize from sunlight. The sugar is what fuels the fungi, as they scavenge the soil for nitrogen, phosphorus and other mineral nutrients, which are then absorbed and consumed by the trees.
 

To communicate through the network, trees send chemical, hormonal and slow-pulsing electrical signals, which scientists are just beginning to decipher. Edward Farmer at the University of Lausanne in Switzerland has been studying the electrical pulses, and he has identified a voltage-based signaling system that appears strikingly similar to animal nervous systems (although he does not suggest that plants have neurons or brains).

Five-thousand miles away, at the University of British Columbia in Vancouver, Suzanne Simard and her grad students are making astonishing new discoveries about the sensitivity and interconnectedness of trees in the Pacific temperate rainforests of western North America. Dr. Simard is a professor with the UBC Faculty of Forestry, where she lectures on and researches the role of mycorrhizae and mycorrhizal networks in tree species migrations with climate change disturbance. Networks of mycorrhizal fungal mycelium have recently been discovered by Professor Simard and her graduate students to connect the roots of trees and facilitate the sharing of resources in Douglas-fir forests of interior British Columbia, thereby bolstering their resilience against disturbance or stress and facilitating the establishment of new regeneration.

They found that the mycorrhizal network serves as a belowground pathway for transfer of carbon from the nutrient-rich deciduous trees to nearby regenerating Douglas-fir seedlings. Moreover, they found that carbon transfer was enhanced when Douglas-fir seedlings were shaded in mid-summer, providing a subsidy that may be important in Douglas-fir survival and growth, thus helping maintain a mixed forest community during early succession.

 
Simard's research indicates that all trees in a forest ecosystem are interconnected, with the largest, oldest trees serving as hubs. The underground exchange of nutrients increases the survival of younger trees linked into the network of old trees. She has found vast underground tree root systems that are kind of like giant brains. Like the neurons in our own brains, trees send messages via their roots. In fact, she says that trees aren't only communicating, but are also sending resources back and forth to help out other trees -- even if they are a different kind of tree. 

Simard calls the older trees (up to 500 years old) "mother trees." Mother trees are the biggest, oldest trees in the forest with the most fungal connections. They're not necessarily female, but Simard sees them in a nurturing, supportive, maternal role. With their deep roots, they draw up water and make it available to shallow-rooted seedlings. They help neighboring trees by sending them nutrients, and when the neighbors are struggling, mother trees detect their distress signals and increase the flow of nutrients accordingly.

 
When mother trees begin to die, they start passing their resources off to the younger trees around them. Simard says it's like the passing of a wand from one generation to the next. Besides being a beautiful way to understand forests, this information also gives us one more reason to stop clear cutting, which is when timber companies clear tracts of land of all trees. It's easier for the loggers, but it takes away the mother trees so they can't pass along those resources to the next generation. With the logging of mother trees, they wipe out whole forest communities, and that's nothing less than attempted ecocide. After learning about the complex life of trees, a walk in the woods will never be the same again.