Derek Ridgley, Peak to Peak. In his 2019 Pulitzer Prize winning novel, The Overstory, author Richard Powers uses a diverse mélange of characters to illuminate the crucial role that forest ecosystems play in supporting life on earth. Perhaps appropriately for environmental fiction, Powers’ book is meandering and moody, a melancholy meditation on the damage that results from humanity’s increasing separation from nature. 

One central character is a maverick biologist who uses pioneering research techniques to suggest that trees are actually social organisms rather than isolated individuals. This fictional character was based on the groundbreaking research of forest ecologist Suzanne Simard, who studies how networks of fungi and roots facilitate interaction between trees and other plants. Expanding steadily in scope, Simard’s research has laid siege to the prevailing crop-oriented dogma of forest management. Her theories challenge all of us to see forests in an entirely new way. 

Simard’s work is the subject of a 2016 documentary film, Intelligent Trees. Her own book, Finding the Mother Tree – Discovering the Wisdom of the Forest, will be published this June. Few people have done more than Suzanne Simard to reveal the inherently collaborative underpinnings of biology, and the invisible networks that permeate and regulate healthy ecosystems. 

Understanding the dynamics Dr. Simard’s research illuminates requires us to fundamentally shift our perspective. We humans are surface-dwellers after all.  When we think about forests we visualize the trees above ground, while the most important ecological action actually takes place underground. We also tend to perceive trees as self-contained individuals, supporting themselves solely from the water and nutrients derived from their own root systems. In truth, many trees are demonstrably communal, social creatures. Forests actually illustrate the proverb that it “takes a village” for an individual tree to truly thrive. 

Trees don’t build this village by themselves; the hidden glue that binds forest communities together is mycorrhizal fungi. The term mycorrhiza refers to the role of the fungus in the plant’s root system. A mycorrhiza is a symbiotic association between a fungus and a plant where the fungus colonizes the host plant’s root tissues. The plant makes organic molecules such as sugars by photosynthesis and supplies them to the fungus, and the fungus supplies the plant with water and mineral nutrients from the soil. Most plant species form mycorrhizal associations, and mycorrhizae play important roles in plant nutrition and soil chemistry well beyond forest ecosystems. 

In forest ecology, these mycorrhizal associations produce a network effect that biologists refer to as a common mycorrhizal network (CMN).  An individual tree may have 15 or more different fungal partners at one time. In addition to other trees, those partners provide links to fungi and vascular plants. The density and diversity of CMN connections in a healthy forest is remarkably similar to the neural networks found in the nervous systems of virtually all animal species. It also bears a haunting resemblance to the network architecture of computer systems, leading some pundits to metaphorically label CMNs the “Wood Wide Web.” 

Suzanne Simard and a growing host of co-researchers have demonstrated that CMNs serve a variety of functions that contribute to the communal well-being of forest ecosystems.  First, CMNs operate like a vascular system that moves water and nutrients (carbon, phosphorous, nitrogen) from one plant to another. Second, CMNs have been shown to transport specialized molecules known as alleleochemicals that influence the germination, growth, survival, and reproduction of the receiving organism. This means that plants actually use CMN for communication. 

The specific behaviors that mycorrhizal networks enable are astounding. Some tree and plant species share triggers to warn their neighbors of pest incursions or to announce the beginning of their germination cycle. Others use CMN to share food and water in dedicated symbiotic relationships. For example, using radioactive carbon isotopes, Simard discovered that birch and Douglas-fir trees exchange carbon in a seasonal trade that benefits both. When the birch trees lose their leaves they receive extra carbon from the firs, and birch trees supply carbon to Douglas-fir trees that are in the shade. 

Simard has identified what she calls “hub ” or “mother” trees that play an outsized role in the health of a forest. Like routers in a computer network, mother trees – the oldest and largest – act as central hubs for mycorrhizal networks. Mother trees shift their roots to make room for seedlings. Just like primates, they also intelligently allocate the water and nutrients they export based upon kinship – prioritizing offspring first, followed by species kin and then unrelated plants. 

It is impossible to overstate the profound implications of Suzanne Simard’s pioneering research. We now know definitively that many trees are social, communal creatures. They communicate with one another. They share resources across species for the benefit of the broader forest ecosystem. They store and share information as conditions change. They are more resilient in species-diverse communities. Forests are social and possess a form of emergent intelligence. Based upon this new understanding, the “plantation mindset” that has governed historical forest management practices must be abandoned.

(Originally published in the June 3, 2021, edition of The Mountain-Ear.)