Key takeaways
- Chaga enters birch through a wound and grows inside the wood.
- Over years it produces the black, sterile conk on the trunk.
- The tree eventually dies, and the fungus then produces its fruiting layer.
- Chaga’s chemistry includes compounds associated with birch.
Chaga and birch are inseparable. This article explains the relationship between the fungus and the tree it grows on.
How chaga infects birch
Chaga spores enter a birch tree through a wound, such as a broken branch or damaged bark. The fungus then grows inside the tree’s wood, spreading as mycelium and slowly decaying the heartwood. See Parasitic and Wood-Decaying Fungi Explained.
The conk
Over years, the fungus produces the familiar black, cracked mass on the outside of the trunk. This conk is sterile and can keep growing for a long time. See Why Chaga Is Not Technically a Mushroom.
A long relationship
An infected tree can live with chaga for many years, but the fungus continues to decay its wood. Eventually the tree dies, and the fungus produces its short-lived fruiting layer.
Why birch?
Chaga grows mainly on birch, though it is occasionally recorded on other broadleaved trees. Its association with birch is also reflected in its chemistry: chaga contains betulin and betulinic acid, compounds associated with birch bark. See Chaga Compounds Explained.
Where it grows
In cold northern forests where birch is common: Russia, Scandinavia, Finland, Canada, the northern United States and occasionally Scotland.
Why it matters for harvesting
Because chaga grows slowly on living trees, responsible harvesting leaves part of the conk and avoids over-collection. See Chaga Harvesting and Sustainability.