Rainy Rambles: Phyte Club Part One: Epiphytes

Published 10:46 pm Wednesday, July 30, 2025

When walking through a forest, you are not just walking through a single ecosystem. Instead, you are passing ecosystems within ecosystems, nesting within each other like Matryoshka dolls.

Any pool of water holds a variety of tiny organisms, even if it is devoid of tadpoles or tiny fish. A single tree may be the home to countless animals, lichens, fungi, and moss, and a patch of moss contains its own collection of spiders, springtails, rotifers, and other miniature beings. 

Let’s take a closer look at those life forms that cover the outside of a tree, mottling the bark with white and green in a variety of shades. You’ve likely seen large Sitka spruce (Picea sitchensis) whose branches are adorned with thick layers of moss, often with bright green licorice ferns (Polypodium glycyrrhiza) sprouting out from the verdant carpet. Or perhaps you’ve noticed large shelf-like conk mushrooms protruding from the trunks of western hemlock — usually dead snags, but occasionally live trees as well.

These are just a few examples of the organisms that rely on our local trees for safe places to live. However, people often wonder whether they harm the trees they grow on. After all, it seems like dead trees are often rife with mushrooms and lichens, and so the questions of whether the tree’s hangers-on hastened its demise.

The answer is: it depends. Mosses, lichens, and licorice ferns are all examples of epiphytes. These are organisms that cling to the outside of the tree’s bark. Once a spore of one of these organisms lands in a suitable spot, it uses the bark’s rough texture to anchor itself securely as it grows and expands. It doesn’t draw any nutrition from the tree itself, instead acquiring food through photosynthesis, and absorbing water from the air or in pockets of rain that gather in the crevices of the bark.

If you were to climb one of our large Sitka spruce, you might notice that the species of lichens and other organisms changes as you go higher up the trunk. The species you find close to the ground aren’t necessarily those that you find high up in the tree. Old man’s beard (Usnea longissima), for example, is a fairly cosmopolitan species that may be found at both eye level and dozens of feet up in the branches. Tree lungwort (Lobaria pulmonaria), on the other hand, prefers the tree’s canopy, and will only be found at ground level if it is blown down during a storm.

Why are some species pickier than others? It all comes down to microclimates. These are small pockets of an ecosystem that are marked by unique amounts of sunlight exposure, humidity, wind, and temperature. Tree lungwort is better adapted to parts of the tree that get comparatively more sunlight than at ground level, and can also weather the more variable temperatures, wind exposure, and humidity at that height. Pelt lichens (Peltigera spp.) mostly grow on the ground and occasionally low on tree trunks, taking advantage of higher overall humidity, more steady temperatures, and more protection from wind while subsisting on less sunlight.

At any level, though, epiphytes are benign presences on the tree’s surface. In fact, they can be quite beneficial to their host. A tree with a thick layer of mosses, lichens and ferns has a small layer of additional humidity around it thanks to their transpiration — the water they exhale increased the ambient humidity. Epiphytes also help insulate the tree, keeping it more hydrated and creating a barrier against extreme temperatures. Some trees which have thick colonies of moss on their branches may grow adventitious roots. These roots grow out of the branch itself, and allow the tree to siphon off extra moisture held in place by the epiphytes.

All of which is to say that there’s no need to remove epiphytes from trees. They do them no harm, and offer them great benefits. Unfortunately, there’s a lucrative trade in dried mosses and lichens for decorative purposes, and much of it is poached. Nurseries and craft stores often have large bags of dried moss for sale. According to Robin Wall Kimmerer, author of “Gathering Moss: A Natural and Cultural History of Moss,” for every pound that was legally collected, 10 pounds were poached, often from old-growth forests. And once the moss is torn away from a tree, it usually doesn’t grow back. This not only harms the tree, but means that all the tiny beings that lived in that moss end up either homeless or dead.

So the next time you admire a patch of moss or lichen on a tree, or look up at a cluster of licorice ferns bobbing in the wind, think of all the ecological benefits they bring to the forest. 

Look for Phyte Club Part 2 in August. We’ll examine how the fungi growing on a tree have very different relationships with their host.

Rebecca Lexa is a naturalist, nature educator, tour guide and writer in the Pacific Northwest. Her new book, “The Everyday Naturalist: How to Identify Animals, Plants, and Fungi Wherever You Go,” was published in June.