FACE IT: TREES ARE BETTER THAN WE ARE.

I love Radiolab, a science podcast available on WNYC public radio.  This one from July, 2016, called From Tree to Shining Tree, completely blew me away.  It’s an interview with Suzanne Simard, a professor of forestry at the University of British Columbia, who studies the symbiotic relationship between trees and fungi that live in the soil and attach themselves to tree feeder roots.  Here is a link to the podcast:  https://www.wnycstudios.org/story/from-tree-to-shining-tree

It’s a shitty story—literally.  Simard grew up in the rain forest of British Columbia and summered there with her family in a rustic cottage in a woods, surrounded by Douglas fir, beech, and cedar.  One day her beagle, Jigs, fell into the outhouse and had to be rescued.  While digging into the hole from the side, she exposed a thick mat of roots of various colors and shapes, all intertwined into a carpet so solid that she could walk on it.  She had no idea what it was, but she was determined to find out.  

So began Simard’s lifelong fascination with what goes on below the forest floor.  It turns out, there was quite a lot going on under her feet:  a super-organism that mines and hunts, feeds and exchanges, stores and releases, warns and communicates.  Physically it resembles a central nervous system and it behaves with a certain “intelligence,” if you define intelligence not in a brain-centric way, but in a behavioral way; i.e., the ability to adapt to changing circumstances and problem solve.  The mat beneath Simard's feet is a symbiotic system of tree roots and fungi that thrives on diversity and cooperates across species for the greater good of the whole.  It has a lot to teach us.

As a forestry expert working for the timber industry, Simard’s job was to understand how reforested trees grow.  She tracked photosynthesis in newly planted trees with a radioactive gas and found that carbon traveled from the leaves down the trunks and into the roots, where it entered a vast underground network of nutrient connections.  She mapped the connections and discovered that the largest and oldest trees were the most connected and formed a hub-like structure with other trees similar to the hub and spoke system used by major airlines. 

But the network wasn’t composed only of tree roots.  Simard noticed white, translucent, hairy, tubular filaments—about 1/10^th the diameter of an eyelash--wrapped around the trees' feeder roots.  These, she discovered, are the filaments of fungi so dense and so minute that there can be seven miles of them in a pinch of dirt.  The knitting together of the fungi’s filaments with the tree’s feeder roots is called a mycorrhizal network.  These interconnections have been found in the roots of ancient fossilized plants and have been studied since the 1600s. 

This is a description of the mycorrhizal network shown above from an article in Scientific American. https://blogs.scientificamerican.com/artful-amoeba/dying-trees-can-send-food-to-neighbors-of-different-species/

..., here is a diagram of the mycorrhizal network for a single 30 by 30 meter plot of British Columbian interior Douglas-fir forest. It shows only the Douglas-fir trees in the plot (green saw-blade looking things, whose size is proportional to tree diameter), and only two species of mycorrhizal fungus. In reality, there would be a few other species of tree and hundreds more kinds of ectomycorrhizal fungi. Hundreds.

The black dots represent places where scientists drilled into the soil and sampled for the presence of Rhizopogon [a fungus, pictured below] encasing tree roots. The straight lines indicate which trees’ roots were found in mycorrhiza samples at each location. The lines around the black dots indicate the known extent of each individual fungus; those of the species R. vinicolor are shaded pink and R. vesiculosus are shaded blue.

The tree with the black arrow next to it was by far the most well-connected tree; it was linked to 47 other trees through eight individuals of one Rhizopogon species and three individuals of another. Conversely, one Rhizopogon individual linked 19 trees, young and old. If this diagram reveals only two fungi and one tree species linked by a finite number of sampling sites, you can imagine the true complexity if all fungi and all trees were added in.

 
This is what Simard calls the wood-wide web.  

Rhizopogon Fungus

Simard verified the symbiotic character of the mycorrhizal network.  Using sunlight and chlorophyll, the tree photosynthesizes CO2 into carbon and oxygen, releases the oxygen back into the environment (yay, trees!), converts the carbon to sugar (yay, trees!), and uses the energy to build bark, branches, leaves, and roots.  But if all the tree had available to it were CO2, chlorophyll, and sunlight,  it wouldn’t be able to grow more than about a foot tall.  It would be too weak to support its own weight, and its root tips would be inadequate to take in enough water for the tree to grow beyond a sapling.  In order to develop into a big, beautiful tree, it needs minerals and water.  Enter the fungus.  

The fungus is a miner.  Its filaments are so tiny that they can penetrate the soil easily in search of minerals.  When the fungal filaments bump into a rock, they secrete an acid which dissolves a tunnel in the rock where the fungus mines its mineral components—phosphorous, magnesium, potassium, and copper.   

The fungus is also a hunter.  It seeks out an insect called a springtail, which lives in the soil and is rich in nitrogen.  The fungus inserts its tubes into the insect and drains it of nitrogen, much like a vampire.   

And finally, the fungus is a gatherer—of water.

The fungus carries these minerals, nitrogen, and water in its filaments back to the tree roots.  It “asks” the tree to soften its roots so the fungus can wrap its filaments around them, and the mycorrhizal exchange begins:  sugar from the tree is exchanged for water, minerals, and nitrogen from the fungus.  In fact, the tree sends between 20% and 80% of its sugar to the fungus, which has no access to CO2 or sunlight and has no chlorophyll; therefore it cannot photosynthesize carbon into the sugar it needs to survive.  The fungus returns the tree’s favor by sending the minerals, nitrogen, and water it has collected into the tree roots, allowing the tree to grow into a big, beautiful member of the forest. 

 

But that’s not all.  The mycorrhizal system is also a savings bank, an early warning system, and a health care delivery system.  Healthy trees use the fungi as a bank, stockpiling excess sugar in the mycorrhizal network for future draws as needed.  Injured trees have been found to send distress signals through the mycorrhizal network in the form of VOCs (volatile organic compounds) to warn other trees when they are under attack by a pest, so that the other trees can emit their own defensive chemicals in anticipation.  And dying trees sometimes dump their carbon into the network, where it is delivered by the fungi to the newest, strongest trees best able to survive.  It’s unclear to Simard whether the trees or the fungi are orchestrating the health care delivery system, but she has observed it.  She says it’s almost as if the trees “were thinking ahead to the needs of the forest as a whole.”  Wow!  Lesson Number One.  The network doesn't operate on the individualist principle of the survival of the fittest, but on the socialist principle of the sacrifice of the individual for the greater good of the group. And this principle doesn't operate only on an intra-species basis.  It also operates on an inter-species basis.

Simard has observed that the paper birch will send carbon to the Douglas fir, and the Douglas fir will send carbon to the Ponderosa pine.  Whatever tree needs the carbon most, gets the carbon.  Wow!  Lesson Number Two.  Cooperation within and across species ensures diversity and survival.  

    

So, let’s all plant more trees.  They capture and store carbon.  They take care of their neighbors.  They promote diversity.  Let's face it:  Trees are better than we are.  

P.S.  For an excellent discussion of whether plants are intelligent, I commend this article by Michael Pollan, my favorite science writer:  https://www.newyorker.com/magazine/2013/12/23/the-intelligent-plant/amp

Keep it real!

Marilyn