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NatureSpeak Articles

Tree killed by Old Man’s Beard?

"What is that stuff hanging off all the dead trees?" she asked on the chairlift, making the logical assumption that whatever it was, it killed the trees. Was this unidentified stuff guilty as charged?

What my friend noticed were tree lichens. The lichens were only so obvious because needle loss had revealed them on the dead trees, not because they aren’t also abundant on live trees. Look from chairlift level and you’ll see green and black stringy lichens on most trees’ branches and trunks. And they’re not murderous, in fact, lichens are more likely to help trees than hurt them.

Parasites grow at the expense of their hosts, which lichens don’t. Lichens instead support themselves with moisture and nutrients from the air. Plants which grow on other plants without harming them are called epiphytes . To differentiate between an epiphyte and a parasite, think of your most recent house guests. If they stayed for one or two nights, contributed to the meals, and left you a nice bottle of wine when they left (unasked), they’re epiphytes. If they’re still sleeping on your couch and eating all your food after a month they’re, well, not epiphytes.

One way lichens (which are classed as fungi) differ from plants is their ability to fix nitrogen directly from the atmosphere. And this is where they are so helpful to forest ecosystems. When they fall they fertilize the forest floor with nitrogen which, in our forests, tends to be in short supply. Each year, lichens can add 2-4 kilograms of nitrogen per hectare.

Lichens are also very important food for a number of animals in our area, especially deer. They are especially important during times when a deep or frozen snowpack prevents the deer from getting at tastier plants below the snow. Other animals which rely on lichens include northern flying squirrels, voles, and mountain goats.

People have different names for the tree lichens – old man’s beard, grandfather’s beard, and Methuselah’s beard – all of which are great names. Properly speaking, the common names for our local lichens have less to do with hairy old men. The green lichens are called common witch’s hair ( Alectoria sarmentosa ) and the black lichens are called horsehair ( Bryoria species).

When there’s no snow in the woods, you can see that the lichen growing on a tree’s trunk normally starts 2 or 3 metres above the ground. This "lichen line" is a rough measure of the average depth of the snowpack – the higher the line, the more snow, and the better the tree skiing.

Tree lichens do best in older forests, perhaps because the bigger trees provide more growing surface. You can see this riding the mountain lifts. In the second-growth forest near the bottom of the hill, lichens are pretty scarce. Get onto the Solar Coaster or Garbanzo Chair, and you’ll see the old-growth forests they pass through have a much heavier cover of lichens. (Except, for some reason, on cedars – don’t ask why, I don’t know.)

In conclusion, your honour, lichens are not killers – they’re as benign and beautiful as Christmas tree ornaments. Innocent of all charges.

Written by: Bob Brett


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