[When drawing this monster, Wes said that he wanted to give it flat teeth specifically because the flat edges of incisors are specialized for chewing vegetables and plant matter. Essentially, he made the tree something of a cannibal. I think it works pretty well with the following discussion of non-animals consuming each other.]
You know, of all the items in the world that can make people so giddy that they get stupid, pruning shears probably shouldn’t be on the list.
And yet I’ve seen homeowners as well as public works employees let the power that a pair of steel shears imparts lead them to some questionable choices while they pruned dead, spindly branches from trees. They approach pruning as if they were swordfighters in a martial arts epic, or people who decide to re-evaluate their phones’ contact lists after a Saturday night out drinking. Either way, they cut with a vigor that borders on hysterical joy, leaving very little when the act is done.
Pruning, however, is a delicate art. As with swordfighting and social interaction, there’s a way to do it that’s right, and several ways to do it that just leave a mess. A bad pruning cut can create a gaping hole of a wound in a tree’s wood that a certain group of parasitic organisms would love to crawl inside and infect.
First, though, before we take a trip into the nightmarish-sounding world of one living organism easing its way into another (ohmigosh, I’ve seen Alien, I know how this is going to end), let’s take a quick look at tree anatomy:
At the base of a tree branch, right where it connects to the tree trunk, is an almost turtleneck-type collar of tissue called the branch bark ridge. This ridge is the part of the tree where new wood will grow after a branch is cut away. The wood that grows back is called either wound wood, which sounds vaguely S&M-ish but isn’t, or callus tissue, which sounds like something the tree should have taken care of on a spa day.
Unlike the patches of dead skin that we loofah away from our heels, calluses at the site of a removed branch are good. They prevent disease organisms from infesting the wood deep within a tree. Too often, though, the branch bark ridge is pruned away along with the rest of the branch. The pruning cut is made flush against the tree trunk, and it’s not just a flesh wound, or, in this case, I guess, a flush wound. Without the branch bark ridge, callus tissue can’t form.
And that’s where the fungus comes in. Like, literally where it gets into the tree.
Fungi are fascinately deceptive organisms. It’s easy to believe that a mushroom is the main part of a multicellular fungus, because that’s the part that we see. More importantly, it’s the part that we eat (assuming the shroom isn’t toxic), and sometimes, we just need to know enough to know what’s going to taste good on a pizza without killing us. It’s all about priorities.
A mushroom is only a reproductive structure, though, a part that pops up when the fungus is ready to release its spores into the wind and go forth and multiply across the land, even if “the land” is just the several-yard radius of the front lawn. What a fungus really is is a collection of filaments called hyphae. Each hypha is a group of cells that looks like a thread and that grows snaking its way through dark spaces, often joining with other hyphae in a big clump to form a mass that’s called a mycelium. Patches of dirt and soil make excellent places for fungal hyphae to develop into more massive organisms.
So do the insides of trees.
If an external wound in a tree isn’t sealed with callus tissue, it leaves the tree’s sensitive inner tissues, the channels that carry water and nutrients from the root to the stem, exposed to creatures that want to devour them. Once fungi make their way into an open wound, it isn’t hard for them to reach their hyphae all the way through the tree’s otherwise hidden nooks and crannies. It’s everything that makes you squeamish when you read in some kind of sci-fi story about a tentacle monster trying to stick its tendrils into any crevasse it can find on the hero’s body, except that it happens on a much smaller scale inside of wood, and it happens every day around the world. Oh, and, in a way, it’s even more violent.
Fungi are heterotrophs, meaning that they have to consume external matter to get the nutrients they need to live. Humans are, too, so we have something in common. However, human beings politely digest their foods inside their stomachs, away from the view of one another. Fungi? Not so much. They engage in what’s called extracellular digestion: they secrete enzymes from their bodies, decompose the substance of a tree outside of themselves, and then absorb the broken-down nutrients through their cells. Imagine if you ate your grilled cheese by slapping your hand down onto it, secreting some acidic chemicals from your hand that decomposed the sandwich into mush, and then absorbing good nutrients from the mush through your skin.
I can’t lie. Part of me finds that a little disturbing; the other part of me is impressed. Would you believe, though, that some plants actually need fungi to do this in order to survive?
The fungi that consume a tree through its innermost heartwood are considered parasitic, meaning that they benefit while the trees that host them suffer. Fungi that eat dead matter are called saprophytic. Many fungi, though, benefit the plants they’re living on as well as themselves when they invade. These fungi are called mutualists, and they most often make their way through a plant’s roots.
Orchids in the wild serve as a widely known example of mutualism. When fungal hyphae invade a plant’s roots, they create a hybrid structure called mycorrhizae. As botanist Hans Burgeff discovered in the early 1900s, when certain fungi attach themselves to orchid roots, they carry nutrients from deep within soil up to the orchid and share them via the channels created when the fungi invaded. The orchids get an extra source of sustenance that their roots didn’t reach; the fungi get a host that provides them with sugars made during photosynthesis. When mycorrhizae are involved, everyone wins!
Hardwood trees like elm and ash trees can benefit from mutualistic fungi, too. A biologist named Stewart Miller has shown that these trees are excellent hosts for the morel mushroom, a tasty fungus that, like many culinary delicacies, can be described as “freakin’ weird-looking.” The tree gets deep-soil nutrients; the fungus gets to suck on some tree sap. Of course, the fungus doesn’t actually produce those delicious mushrooms until the tree starts dying a little, sending the fungus into a Jor-El-like “last-ditch attempt at survival” mode, so there’s that downside.
As destructive as the activities of lignicolous, or wood-dwelling, fungi may seem it’s important to remember that fungi play crucial in outdoor habitats. They break down the dead tree stumps that otherwise would pile up on the forest floor, and they make the nutrients from dead matter available for plants to use so that they can grow. Even when fungi hollow out a tree trunk, they create holes that creatures like squirrels and owls use as homes. (Fun fact: standing dead trees that animals occupy are known as snags.)
Basically, thanks to fungi, a dying tree still gets to participate in life, and without all the hassle of returning as a zombie-tree or as some kind of cannibalistic tree-monster as seen in the drawing above. That seems like a pretty good arrangement to me.
For a list of some common wood rot fungi, click on this link. Have your own experiences with tree snags or with lovely lignicolous fungi? Leave a reply and let us know! (Be sure you’ve clicked on the individual post link to see the reply box below!)