Susan Simard received her PhD in Forest Science and is a research scientist who works primarily in the field. Part of her dissertation was published in the prestigious journal Nature. Currently she is a professor in the department of Forest and Conservation Sciences at the University of British Columbia where she is the director of The Mother Tree Project. She is designing forest renewal practices, investigating the ecological resilience of forests, and studying the importance of mycorrhizal networks during this time of climate change.
Susan’s research over the past 30 plus years has changed how many scientists perceive the relationship between trees, plants, and the soil. Her intuitive ideas about the importance of underground mycorrhizal networks inspired a whole new line of research that has overturned longstanding misconceptions about forest ecosystems as a whole. Mycorrhizae are symbiotic relationships that form between fungi and plants. The fungi colonize the root systems of plants providing water and nutrients while the plant provides the fungus with carbohydrates. The formation of these networks is context dependent.
Simard discovered that fungal threads link nearly every tree in a forest. This includes trees of different species. Carbon, water, nutrients, alarm signals and hormones pass from tree to tree through these underground networks (as well as above ground). Resources tend to flow from the oldest and largest trees to the youngest and smallest. Alarm signals generated by one tree prepare nearby trees for danger. And if any tree is dying it often sends carbon to its neighbors.
At this point in time others researchers have replicated Simard’s major findings. Resources do travel among trees and plants via underground networks. Most ecologists also agree that the amount of carbon exchanged among trees is sufficient to benefit seedlings as well as older trees that are injured, entirely shaded, or severely stressed. Most are also in agreement that trees pass nutrients, information, and do support one another. This reciprocity undermines the dogma of individualism and competition for the fittest as the primary driving force of evolution.
Simard believes that an old growth forest isn’t a group of solitary individuals who tolerate each other and compete for resources. Instead she calls a forest a cooperative system that behaves more like a single organism. The trees, understory plants, fungi, and microbes in a forest are so intimately connected that other scientists have described them as super organisms. There is conflict and negotiation, reciprocity and perhaps even altruism. Recent research by Simard and others suggest that mycorrhizal networks also link prairies, grasslands, chaparral and arctic tundra, indicating that life stretches across the entire planet by way of land.
In North America most trees are generalists, forming symbiotic relationships with hundreds of fungal species. In one study an especially old tree was linked to 47 other trees and projected to be connected to at least 250 more. Depending upon the species, mycorrhizal networks supply trees and other plants with up to 40 percent of the nitrogen they receive, and as much as 50 percent of the water they need to survive. Simard also found that denuding a harvested forest of all trees, ferns, herbs and shrubs – a common forestry practice – was often harmful to the entire ecosystem.
The language Simard uses when speaking about the complex relationships that occur between the trees and the fungal networks beneath them is a source of contention. For example, Simard uses the word “Mother tree” to describe the oldest, largest, and most interconnected trees in a forest. She uses this phrase to evoke the capacity of trees to share resources and nurture those around them even if they are not kin, although she has also established that trees do seem to favor their offspring.
The idea that trees are social beings – living beings – has profound and urgent implications for how we presently manage our forests.
Plants and fungi oozed out of the ocean onto land somewhere around 400 – 600 million years ago. Plants obtained energy by eating sunlight but they couldn’t extract mineral nutrients from the barren rock. Fungi couldn’t photosynthesize but they could digest rock and transform it into soil, so together, the two formed a partnership and spread across the land. The resulting forests helped create an atmosphere that continues to provide us with the oxygen we need to breathe.
Forests also respire (breathe) filling the air with water vapor, fungal spores, and chemical compounds that seed clouds with moisture, cool the earth by reflecting sunlight, and provide much needed precipitation to inland areas that would otherwise be in a state bordering on drought or worse.
Additionally, forests store an immense amount of carbon in their leaves and trunks as well as in roots and the soil below. The statistics vary but each year the world’s forests capture at least 24 percent of global carbon emissions. Deforestation diminishes that effect dramatically. When a mature forest is burned or clear – cut the planet loses one of its most natural and effective systems of climate regulation – not to mention the cheapest.
When colonial peoples came to this country in the 1600’s forests covered one billion acres – close to half the total land mass. By the beginning of the last century ravaged forests were the norm with a third of the forests gone. By the end of the century loggers were forced to replant trees in order to continue to harvest trees. And although clear cutting isn’t as common as it once was it is still practiced on about 40 percent of the land in this country.
When we destroy an old growth forest we collapse a system that is essential for survival. Although young forests now cover parts of the Northeast, less than one percent of old growth forest remains intact. We have less than 3 percent of old growth forest left in the entire country.
In a thriving forest a lush understory captures huge amounts of rainwater and dense root networks provide nutrients and stabilize the soil. Logging disturbs the forest floor increasing the chance of landslides and floods, stripping the soil of nutrients and releasing stored carbon into the atmosphere. When soil flows into the rivers and streams it can kill fish and other aquatic creatures not to mention that the felling of trees harms and evicts countless species of birds, mammals, reptiles, amphibians and insects.
Simard’s research also suggests the crucial importance of leaving seed trees when cutting. When a seed germinates in an old growth forest it immediately taps into an extensive underground community of interspecies partnerships. Conversely, when a plantation of trees is planted after a clear cut there aren’t any ancient root and fungal systems to support the tree. As a result these new trees are much more vulnerable to disease and many die. Simard believes that leaving the mother trees intact will improve the health and survival of future seedlings.
Simard is presently concentrating on how the underground networks could be disrupted by environmental threats during climate warming, as a result of logging, and pine beetle infestations (that are killing western trees in less than four years). She believes the underground networks will probably survive but whether they will be beneficial to native plants etc. remains to be seen.
One of the fascinating aspects of Simard’s recent research demonstrates that trees who are dying as a result of climate change continue to send carbon and warning signals to the seedlings/trees of the new species of trees that will eventually replace the original forest. The only caveat warns Simard is that we must leave some trees that support the complex mycorrhizal networks below, or the forest will not regenerate.
Susan’s love for trees and lifetime dedication to saving forests began when she was a child. She went into the woods to watch her uncle log western cedar for his living, and saw that logging could be done in a way that would allow the forest to thrive. I admire her vision, her commitment to saving trees, but also the fact that she refuses to abstract or distance herself from the research she does. She reminds us that trees are living beings who communicate and cooperate with one another and their surroundings both above and below ground. In the final analysis it is not education that creates change; we save what we love.
The next time you are walking by a tree think about the fact that humans have four photo – receptors with which to see – red, green, blue, and light/dark – trees have eleven. When you are gazing at a tree, it may also be looking back at you.
Postscript: By the time this article is printed Susan Simard’s new book “Finding the Mother Tree” will probably be published, and I will be one of the first people to read it. Susan’s work has the potential to change the public’s understanding of how forest ecosystems really operate. My earnest hope is that her ground-breaking research and this book will help shift the way humans perceive our forests so that we can save them before it’s too late.