Rae (00:22):

As you walk through the forest of the North Country, it's hard to ignore the towering trees, motionless, quiet, objects of the forest, but perhaps there are more to trees than meets the eye.

Rae (01:04):

Thank you for listening to Naturally Speaking, the Nature Up North podcast. In this episode, we're going to explore the secret life of trees, how they share nutrients, communicate, and even recognize their kin. This is all possible thanks to the "wood wide web," which is a coined term for the underground network of fungi that link trees together. Trees possessing these abilities begs the question "are trees intelligent?" Stay tuned to the end of the podcast to find out! Let's dive into how this connection between tree and fungi work. To help us answer this question, we need to gain a better understanding of fungi itself. To aid in this process, we have Claire Burkum, who has a Master's degree in the study of fungi and is very knowledgeable about them. Claire also works right here in the North Country at St. Lawrence University as a general biology course manager. So let's first start with what is a fungus? Are they just the mushrooms we see all over the forest? Let's turn to Claire Burkum to answer this question.

Claire (02:15):

So when we see a mushroom out in the woods, we're walking along and we see a mushroom, that mushroom is similar in function to the apple on the tree, all right. So it's really just there to spread spores. The creature though, the thing that's getting nutrients, that's digesting stuff, that's bringing stuff into it, that's having metabolism. That's all filamentous mycelium that's in the ground or connected to the tree root.

Rae (02:44):

Wow. So the fungal creature itself is all underground and it's composed of mycelium. Well, what is mycelium?

Claire (02:53):

So myceium is a general term that describes, basically a mass of hyphal cells of fungi. It can refer to many different types of fungi. It's kind of like saying tissue or the body of a fungus. So it's not specific to certain types of fungi. So any fungi that make linear filament thread-like structures, when you have it growing in a clump of some type, we call that mycelium.

Rae (03:28):

So mycelium is composed of filaments that can connect to trees. But the actual connection with plants has its own name called mycorrhiza. And this is actually the specific field of study that Claire Burkum received her Masters on. So let's turn to her to get a definition.

Claire (03:46):

Mycorrhiza is a connection between a fungus and a plant root, and it's its own structure, its own unique thing.

Rae (03:59):

So there are two types of mycorrhiza, so two types of fungi and root interactions, that occur in the North Country. Ectomycorrhiza and ectomycorrhizal, most trees form ectomycorrhizal connections, and these trees cannot communicate with the trees that form endomycorrhizal connections. Here's Claire, to explain the difference.

Claire (04:22):

So ectomycorrhizae, we call them ecto because the fungal partner never actually goes inside of a plant cell. Endomycorrhizae, they actually penetrate the cell wall, they're able to kind of suppress some of the immune function of the plant and get into the plant more.

Rae (04:44):

Now this connection between trees and fungi is why trees can be linked together in a massive interconnected, underground web, the wood wide web. The wood wide web, however, has a misconnotation. It's more complex than just one web here's Claire with an explanation.

Claire (05:04):

Now some fungi are very specific, like there's certain ectomycorrhizal fungi that only grow with birch - that's it, that's all they want to deal with. There's other fungi that are more generalists they'll work with whoever's roots are around as long as they form ectomycorrhizae.

Rae (05:23):

So let's think about this for a second. First off, there are both endo and ecto mycorrhizal fungi and both of them linked to trees together, but in two separate networks. Then on top of this, there are different types of ecto and endo fungi, and each type has its preferred species of trees that they will interact with. So in reality, the wood wide web really isn't just one web. There are several different webs, networks upon networks of connections in which one tree can be a part of many different ones at the same time. So what about here in the north country? What trees and fungi are a part of this web? Well, Claire Burkum informed me that there are many ectomycorrhizal fungi species right here in the North Country, probably thousands of species. Some genera, which is plural for genus, the grouping of organisms that rank just above species include Russula, Amanita, and most of the Boletus. If you're a fungi enthusiast, check out a longer list supplied on this podcast page. Connecting to these fungi, there are many mycorrhizal trees in the North Country too, such as birch, beech, oaks, firs, hemlocks, pines, and more. We also have trees that form endomycorrhizal relationships such as maples and ashes. So this interconnected web between these trees and these fungal species is right below your feet.

Rae (06:59):

So why do fungi connect to trees? Well, this connection allows them to be in a mutualistic symbiotic relationship with each other. To unpack what that means we turn back to Claire Burkum.

Claire (07:13):

My definition of symbiosis is quite literally things that live together. When you have a symbiotic relationship where both parties benefit, then I use a more specific term called a mutualism. Most mycorrhizae probably fall under a mutualistic category.

Rae (07:31):

So this mutualistic relationship benefits both the trees and the fungus, but how? Well, fungi have no photosynthetic capabilities. They cannot use sunlight and carbon dioxide to make sugar like trees can. So in this mutualistic relationship, the fungi get sugar from the trees - consuming 30% of what the trees make. And it's this sugar that gives the massive mycelium its energy so it can grow and scavenge for nutrients. In return, the fungi passed some of the nutrients back to the trees, in particular phosphorus and nitrogen. Here's Claire to tell us why.

Claire (08:13):

Fungi are better at getting some nitrogen and some phosphorus out from where they're living than trees are. They typically just have better chemical reactions to be able to do that.

Rae (08:26):

On top of getting needed minerals trees, are also gaining access to a delivery system. Trees can utilize the fungal web to pass nutrients such as the phosphorus and nitrogen, but also carbon and water to all other trees that are part of this connection. Suzanne Simard, a professor of forest ecology at the University of British Columbia, and her colleagues were able to trace the flow of carbon by using a form of carbon called an isotope, which has one more neutron than the carbon in the atmosphere. She demonstrated that a paper birch that was given this carbon isotope passed it to Douglas fir via the mycorrhizal network. Using two different types of isotopes, these scientists confirmed that carbon is passed back and forth between these trees. In fact, paper brch are found right here in the North Country and may be exchanging nutrients right underneath your feet.

Rae (09:28):

But the question still remains. Why are nutrients being moved between trees? In an interview with the Smithsonian Magazine, forester Peter Wholleben describes a passage of nutrients as a humanlike friendship between trees. Referring to two beech trees, Wholleben said, "these two are old friends. They are very considerate in sharing the sunlight, and their root systems are closely connected. In cases like this, when one dies, the other usually dies soon afterward because they are dependent on each other." This makes it seem like trees pass nutrients out of kindness to one another. Claire Burkum brings up another possible reason.

Claire (10:12):

Typically things just go from right diffusion goes from high concentration to low concentration. So if we just didn't have as much carbon here, but we still had connections, and we still had, if we put sugar water in a certain place that sugar's gonna dilute in a certain direction in water, and it's not because anything desires it or wants to give it, or it's just how molecules move around.

Rae (10:39):

The review by Monika Gorzelak, a scientist at the University of British Columbia, and her colleagues confirms that many researchers equate the transfer of nutrients between trees with a source-sink relationship. One tree that has an abundance of a certain nutrient due to where it's living, acts as a source, and due to diffusion, this nutrient is passed to the sink, which are trees that lack this nutrient. In that sense, many different types of nutrients are all flowing back and forth between this web from high concentrations to low concentrations. This would in a sense level the playing field, allowing all the trees that are connected by this web to have a more equal access to resources. Does the source-sink theory undermine the concept that trees are willingly exchanging nutrients? Perhaps it does, but this web holds more mysteries than just nutrient passing.

Rae (11:48):

Wow, those people sure are talking loudly. Isn't it nice how quiet forests are? Well, actually trees are communicating too, but we just can't hear them because they're talking via the wood wide web. Trees can send defense signals to alert each other of a drought, disease, or even pestd. They do this in two different ways. One way is via the air in the form of an odor. This is similar to humans and our perfumes and deodorants. In Peter Wholleben's book, The Secret Life of Trees. He describes the phenomenon in common North Country trees, such as oaks, spruces, and beeches. When a tree is being munched on by a caterpillar, a beetle or some other pest, it can release a distress signal. Scientists have noticed that trees have different signals for different predators. Apparently trees can associate the saliva of threat with a specific defense pheromone that warns other trees what is in the area and will soon eat them. To defend themselves trees have two secret weapons. The first one is that trees can release a substance known as tanin. Here's Claire Burkum with a quick definition of tannin

Claire (13:19):

Tannins are something in leaves that insects, it's harder for insects to process that as food.

Rae (13:27):

This effectively deters the pest from eating the leaves. Now, if this does not work, trees can also release pheromones that attract the predator of that pest, effectively causing the threat to be eaten or to flee away. Sending pheromones can elicit a response in mere minutes, but it only works in right weather conditions. And it only warns trees that are close by and upwind. So how do trees warn others of danger? Well, trees can send chemical, hormonal, and slow electrical pulses through this fungal web that also alerts trees to threats. In fact, researchers Suzanne Simard and Edward Farmer have found that these electrical pulses are similar to neurotransmitters that many animals - have including humans.

Rae (14:19):

Now, scientists are not claiming that trees have a brain. In fact, the research on plant electrical pulses is new and far from complete. But it's surprisingly not the only ability trees and other plants have demonstrated that are perplexing to researchers. Studies have shown that trees are able to recognize their young and their children. To demonstrate this Suzanne Simard conducted an experiment with the mighty Douglas fir. She planted them next to unrelated trees and next to their kin, she injected carbon isotopes into the test Douglas fir and found that it passed more of this carbon to its kin than to the unrelated species. Having replicated this experiment several times, the answer does not appear to be due to the sink-source theory discussed previously. So how do trees recognize their young? Well, scientists do not know. Current theories involve biochemicals at the tips of the roots, or perhaps by scent. Scientists are continuing to research this baffling and thought provoking subject that maybe one day we will know the answer to. I hope hearing that trees share nutrients, knowledge, and recognize their kin has altered your perception about them. Perhaps you're even wondering - now are trees intelligent? Claire points out an important thing to consider when pondering this question.

Claire (15:51):

So, when you asked me about whether I think trees are intelligent, I think it really comes down to our definition of intelligence. And so if we're ascribing human emotions and human intelligence to trees, that makes me balk, I don't like that as much. Simply because they might be intelligent in some completely other way than humans are intelligent, they might feel things in a different way.

Rae (16:21):

Though. We'll probably never know what it's like to be a tree, I hope the next time you walk among the North Country woods, you will appreciate trees, not as objects of the forest, but as impressive creatures that have a complex life of their own. A special thanks to Claire Burkum for joining me to make this episode of Naturally Speaking possible. We hope you enjoyed it. Get up and get outdoors with Nature Up North!