Pt. 1: The Underground Network
By Susan Rothrock Deo
Photos by Susan Deo, except sequoia and bristlecone pine by Judy Herman
Do you have a favorite tree? We have one down the street I call the singing tree because it’s often full of birds that I can’t see among the leaves but can hear chirping and singing. There are several bird feeders nearby and the birds use the tree as a perch while they wait their turn at the feeders. When I was young, a friend and I would ride our bikes to the country railroad tracks between our family farms and walk up a little hill to a tree on top. We’d play in the shade of its spreading branches or climb the strong almost horizontal one at just our height to sit and watch the rare train go by.
We don’t have many native trees here in the South Bay–several willows and the Catalina cherry–but there are many California natives and nonnatives in homes and parks nearby. Not far from our homes are thousands of acres of forests that can feed our spirits and help our ecosystems stay healthy and strong. Trees provide us food–like oranges and avocadoes–shade, beauty. They also provide homes for insects, birds, and mammals. Recently scientists have even discovered whole mini-ecosystems in the crooks of branches high up in some coastal redwoods: complete with soil, plants, and animal life. How many of us have happy memories of being in a tree house as children or adults, as well? Let’s look at some of the wonder of trees.
Trees are green plants that come in all shapes and sizes, but they all start as seeds. Imagine, most seeds you can hold in your hand (granted, a pretty BIG hand if it’s a coconut palm) but trees can mature to many times your height, even become the largest organism on the planet, our giant sequoia, or the oldest living organisms, our Great Basin bristlecone pines. There are evergreens with needles, like the ponderosa pine, broadleaf trees like the coast live oak, and tall willowy palm trees.
Every tree, like all land plants, searches for two things, light from the sun and water from the ground. The moment a seed breaks open, the roots begin their journey down into the ground, establishing an anchor to hold the new tree upright, searching into the soil for water and minerals. First the tap root, the central largest root, heads deep down. It sends out lateral roots that intertwine with the roots of other trees or plants around it. Trees can signal danger to each other through these adjoining roots, and an older tree can actually feed a sapling tree. It’s difficult for a small tree to survive in the shade of the forest. The mature trees block the sunlight, but older trees can give up some of the sugar they make to help the saplings survive.
Scientists are still learning what intriguing things happen beneath the forest floor. The roots of trees also intertwine with each other and with the root-like hyphae of local fungi (like mushrooms and conks, which are the above-ground fruit of these fungi). This makes what are called “mycorrhizal networks.” The trees give the fungi some of the sugar they make, and in return the fungi help the tree gather water and nutrients from the soil. Through this network, trees communicate with other trees of their own species, with trees of other species, and with the fungi. They can signal danger, like disease or insect infestations, for example. Deforestation can upset this network, affecting tree growth and leaf shape and the forest’s defenses against disease and harmful insects. Scientists are studying ways to manage more carefully the taking – or not-taking – of trees to preserve these precious forest communities.
Trees are undoubtedly interacting with many more living things beneath the surface, too. Scientists report that in one tablespoon of soil there are seven BILLION organisms. So much is going on beneath the surface of a forest. If you’d like to learn more about the role trees play, try some of the resources listed below. Next time stay tuned for some insight into the ABOVE GROUND life of trees!
For Further Reading:
Do trees talk to each other?
Underground network of trees and fungi:
Two books you might enjoy that include a lot of current information about trees.
Lab Girl by Hope Jahren, 2016 (a scientist’s memoir)
The Overstory by Richard Powers, 2018 (Winner of the Pulitzer Prize in Fiction)
Learn how Katherine Olivia Sessions transformed San Diego with her love of trees in the first half of the 20th century in this children’s picture book.
The Tree Lady: The True Story of How One Tree-Loving Woman Changed a City Forever, by H. Joseph Hopkins, illustrated by Jill McElmurry, 2013