web of life

My aunt recently sent me an article from Smithsonian magazine about the research being conducted into “communication” between trees.

The topic gained notoriety with the publication of “The Hidden Life of Trees,” by Peter Wohlleben in 2016. The book compares tree communication to human communication and even emotions, such as a description of a tree crying for help when attacked by voracious insects. The storytelling technique certainly caught readers’ attention and made the book a best seller. Most tree scientists dismiss the possibility of an emotional life in trees, but they nearly all agree that trees do communicate with each other – just not in a way we can easily understand. For instance, acacia trees in Africa emit ethylene gas when giraffes start chewing on their leaves. As other acacias detect the gas, tannins accumulate in their leaves to make them less palatable to a hungry giraffe.

Nearly all trees are connected in the soil by unimaginable networks of fungi called mycorrhizae. The basis of the relationship seems to be fairly simple. Fungi living in the soil grow root-like structures called mycelia which twine their way from tree root to tree root, making intimate connections with each root they encounter. Along the way these mycelia are scavenging nutrients from the soil. Meanwhile the trees above are soaking up sunshine and converting that energy to sugar. Fungi do not photosynthesize, so in exchange for a hit of sugar from the tree root, they deliver nutrients in return. But that is just the beginning of the collaboration. There is evidence that trees use mycorrhizae (networks of fungal mycelia) to communicate with each other and even to help or harm each other. Tree roots have been caught sending electrical signals and even sounds at a frequency inaudible to humans. Our understanding is in its infancy, but we know enough to fuel some serious questioning of our own relationships with trees.

Suzanne Simard, a researcher at the University of British Columbia, theorizes that in mature forests there are “hub trees” that are often the oldest and/or largest trees in their vicinity. Her research suggests that these trees share their resources with smaller trees nearby, particularly when those trees are stressed. Simard’s research is in the old growth rainforest of the Pacific Northwest. Last year when I was wandering similar forests in Oregon, I sensed the complexity of that very special ecosystem. The living trees are big and old, and the ground is covered with “dead” trees in varying stages of decay; new life surging forth from their remains. I could only speculate on how many layers of organic remains were between my feet and mineral soil. I realized that it is preposterous to think that the living trees depend only on themselves. Clearly that ancient web of life is intricate and connected.

It feels to me as if we are stumbling around in the dark as we try to understand what is happening in the forest. We have measured increased growth rates after thinning trees, so it seems like the thing to do, and yet we really don’t understand how trees and the organisms in the soil depend on each other. I have done extensive thinning here in Peacham, and last year on our woodlot in Guildhall. The two woodlots have spots that were clearcut about the same time. I have noticed that the trees in Guildhall are growing considerably faster than their contemporaries in Peacham despite the fact that our soil in Peacham is deeper and more fertile than the soil in Guildhall. I think it may be because the land in Guildhall was never cleared for agriculture. While the web of tree trunks was cleared away in both places, the web of soil life in Guildhall was never disturbed.

We don’t live in a rainforest of huge trees and undisturbed ecosystems. The mature forest found in Vermont by European settlers had had several thousand years to establish interrelationships of many kinds – between individual trees of the same species, or trees of different species that evolved to complement each other’s biology, or between trees and the numerous plants that inhabit the forest floor or grow in the crotches of old trees. In the soil a whole other world had evolved with mycorrhizae forming everywhere, intimately connected to the plant roots sharing the soil. Small creatures, from ants to centipedes to spiders to moles and woodchucks, all formed relationships with the trees.

When that millennial forest was cleared, not just the trees disappeared. The soil fungi dependant on the trees disappeared, as did unknown numbers of other species of plants, insects, spiders and more. The whole web of life, complex in ways we do not begin to understand, was torn to shreds. For a short period of time, perhaps a century or so, that land was farmed, the soil growing grass or other crops. New and different webs began to develop, but in such a short period of years they were not complex webs.

Now most of the land that our ancestors cleared has grown back to trees. We walk through our woods and see it as an undisturbed, stable ecosystem. I think that what we are actually seeing is a forest in its infancy. Our human timescale is too short to appreciate what is occurring. We are watching today as much of the balsam fir that seeded in as the farmland was abandoned 70 years ago is now dying. An insect, the balsam woolly adelgid, is hastening their demise, but with or without that insect, or our own interference, those balsam trees are in the process of returning to the soil.

Left to rot, the fallen fir will feed a horde of fungi, ants, centipedes, etc. A yellow birch seed will fall on a broken off stump, find a comfy, moist home, and germinate. Amongst the broken branches of the fallen trunk an acorn will do the same, or a sugar maple will quickly shoot up hoping to avoid the dangerous teeth of a browsing deer. And seeds of the fir trees themselves will join the competition.

Under the surface, the fungal mycelia will thrive on decaying roots. We have studied common fungi that appear to cause harm to valuable trees. Armillaria is a well known group of fungi that we associate with root rot in trees. They can live anonymously on roots for years and then creep upward between the bark and wood of the trunk above, eventually killing the tree. We know that there are also beneficial fungi, also spreading mycelia from root to root. It makes sense that these fungi are competitive. I suspect that in a fully mature forest soil ecosystem a tenuous balance is achieved. The networks of mycorrhizae somehow come to terms with each other, probably with a mixture of competition and cooperation that we cannot yet fathom.

Did I do more harm than good by thinning the trees in Guildhall? Did I inadvertently cut some hub trees and sever some vital lines of tree communication? Or is the real driver of tree growth in the soil, still undisturbed and ready to support the chosen trees above? We don’t begin to know the answers. Perhaps our grandchildren will.