Monthly Archives: September 2018

Forest Feature: Fungi

Mushrooms bloom from a downed log

Our Forest Feature for September is this “fun guy” – the fungi! Fungi are incredibly diverse, making up an entire kingdom of organisms. We have fungus among us, everywhere we go.

But our favorite fungi live in the Pacific Northwest’s national forests.

Fungus grows from the side of a mossy log

Fungi and moss help with the decay of a log on Brice Creek Trail in Umpqua National Forest, Oregon, on the Cottage Grove Ranger District May‎ ‎28‎, ‎2017. USDA Forest Service photo.

If you shopping at a grocery store, you might buy mushrooms that were grown on a farm. But you can also buy wild mushrooms, and some of these are collected from National Forests!

Have you heard of the humongous fungus? How big do you think it might be? As big as a basketball? As big as a car? It’s even bigger!

A genet is a genetically distinct organism. Some genets of the Armillaria ostoyae, also called the “shoe-string fungus,” grow very, very large. Several of these fungi genets are living in the northeastern part of the Malheur National Forest in eastern Oregon, and one of them has been named the “humongous fungus” because it’s the largest known single fungus organism in the world.

It’s as large as 1,665 football fields combined — that’s 3.4 square miles in size! It’s believed to be 2400 years old.

This “humongous fungus” is not good for the trees it colonizes. It kills and decays the root systems of certain conifer trees, resulting in Armillaria root disease.

Armillaria ostoyae mushrooms

Armillaria ostoyae mushrooms, sometimes called “honey mushrooms,” October 7, 2010. USDA Forest Service photo by Kristen Chadwick (USDA Forest Service, Region 6, State and Private Forestry, Forest Health Protection, Westside Service Center).

If a tree is infected, you might see a scalloped ring of mushrooms emerge from its base after the first fall rainfall. Or, you might see clusters of smaller, round mushroom caps. At other times, you may see a thin layer of white fungus, like paint, on the tree when mushrooms aren’t present. If you look at the roots of a fallen tree that has hosted the fungus, you might see black “shoe strings,” or rhizomorphs, which the fungus uses to spread from tree to tree below ground.

If you see signs of Armillaria root infection, be careful – some trees around might be dead or dying, and could fall at any time.

A stand of dead standing and fallen trees affected by a root fungus

A grove of Douglas Fir trees affected by the Armillaria ostoyae fungus, which causes root disease. As the infected conifers die, other species – such as western larch and Ponderosa pine – may grow to take their place, while the dead trees provide important wildlife habitat. USDA Forest Service photo by Kristin Chadwick (USDA Forest Service, Region 6, State and Private Forestry, Forest Health Protection, Central Oregon Service Center).


Has anyone ever warned you not to eat mushrooms that you find outside? Mushrooms are produced by some fungi to help them reproduce by opening up to spread spores. And one reason fungi sometimes have a bad reputation is some mushrooms are toxic – it takes a lot of training to know which are poisonous and which are safe to eat.

Lots of people enjoy collecting wild edible mushrooms and other fungi as a hobby.

In Pacific Northwest forests, morels, matsutakes, chanterells, are some mushrooms people like to collect to use as food.

Another type of fungi, the truffle, grows in the ground, but is also popular with foragers.

If you want to try collecting mushrooms or truffles, contact a local mycological society to find out what mushrooms grow in your area, and how to get started. Some species are endangered and should not be disturbed. You may also need a permit to collect mushrooms at certain times of year on National Forest land – contact your local Ranger District office for more information.

Chicken of the woods mushrooms grow from a standing tree

Chicken of the woods mushrooms grow from a tree trunk on the Olympic National Forest ‎September‎ ‎16‎, ‎2011. USDA Forest Service photo.

While some can cause problems, fungi actually play a very important role in forest ecosystems. By decaying vegetable materials like wood and leaves, they help make nutrients more accessible to insect larvae, worms and plants. This decay is also neccessary for removing debris from the forest floor, and creating healthy soil that new plants and trees will need to grow. And, like people, many animals enjoy foraging for and eating wild mushrooms and truffles that grow in our forests!

If you’re an educator who would like to explore Pacific Northwest fungi with your students, you can find more information, activities and lesson plans at the below links.

More information:

A thready orange fungus resembling ocean coral grows from a bed of moss and shamrocks on the forest floor

Orange coral fungus grows on the Olympic National Forest, Washington, December‎ ‎4‎, ‎2015. USDA Forest Service photo.

Source information: Forest Features highlight a new Pacific northwest species (or sometimes family, order, kingdom, or genus) each month as part of the USDA Forest Service – Pacific Northwest Region’s regional youth engagement strategy. If you’re an educator who would like more information about this topic, or other ways the Forest Service can incorporate Pacific Northwest environmental and forest science in your classroom, email us at