Chaga (Inonotus obliquus) is a parasitic fungus that is widely distributed in the circumboreal region of the Northern Hemisphere. It forms sterile black conks mainly on Birch (Betula spp.), but also on other deciduous trees. When the host tree dies, which may take 50-80 years, it will form fruitbodies that develop under the bark of the tree and are hardly visible. The sterile growths are harvested because of their (presumed) health benefits. Over-harvesting, especially near settlements and along roads into the northern birch forests can be local and form a regional threat. The state of Alaska (USA) limits harvesting of all conks (excl. Laricifomes officinalis) on public land to 10,000 lbs per year per person. Poaching on private lands is becoming a problem in some parts of the USA and northern Europe. However, the species is common and widespread in Eurasia and there is no evidence of declines. It can be locally abundant where suitable habitat exists. Therefore, it is assessed as Least Concern (LC).

This is a predominantly circumboreal species (Gilbertson and Ryvarden 1986, GBIF 2024), known from Canada, USA, United Kingdom, Norway, the Netherlands, Belgium, Germany, Austria, Italy, Denmark, Czechia, Estonia, Latvia, Lithuania, Finland, Sweden, Poland, Belarus and the Russian Federation.

It is a widely distributed and common species globally. It is very common in northern Europe and typically with several trees colonized within stands. Collecting is not thought to affect its status in northern Europe. In Russia 1–20% of the trees in a natural birch stand show signs of infection (Kuzmichev et al. 2001).

Inonotus obliquus is a parasite and necrotroph, mainly on Betula species, but also on Alnus (e.g. in northern Europe). It forms sterile tissue in the tree (the conk, also called Chaga), and after the tree dies, mature sexual fruitbodies develop under the bark. A Chaga only produces sexual fruitbodies after the death of the host tree. Harvesting full Chaga conks eliminates the ability for Chaga to reproduce. Its spores are beetle and wind dispersed.

The most significant threat to Chaga is from commercial foragers and loggers. In Canada, loggers are harvesting birch wood which may have Chaga growing on them. In Alaska, every non-timber forest product harvester is legally permitted to harvest 10,000 lbs of Chaga and other conks (excluding Laricifomes officinalis) per year, with no regard to the sustainability of the conk or the survival of its host tree. Commercial foragers are already exploiting this quota. Alaska has not set any guidelines for sustainable harvesting of the conk, despite the fact that improper harvesting techniques can cause damage to the tree and eliminate any potential future growth of Chaga. It is traditionally used in Russia for making tea and for medicinal purposes, but is a common and widely distributed species, as is its host Betula, and there is no indications of decline from Russia.

Its sterile growths are harvested because of their (presumed) health benefits to make tea and other health products. Chaga is also being studied extensively for its anti-cancer, anti-fungal, anti-diabetes, and anti-bacterial properties, and even in HIV research.

Some botanists and health writers, such as Arthur Haines and David Wolfe have produced educational videos and books informing individuals on how to conserve their Chaga usage. It is unknown if efforts are being made to track the population of Chaga while commercial Chaga foragers and sales of Chaga have grown significantly over the past decade. A 2004 assessment of sustainable commercial harvesting in Khabarovsk and Primorsky Krais, Russia concluded that commercial harvesting of Chaga did not endangered this abundant conk, but that the species could be locally over-harvested. Without efforts at enhancing production, the harvest might become economically unsustainable, as collectors need to travel further from towns and cities to find specimens. However, further research is likely needed as the demand for Chaga has grown significantly since 2004. Forest ecologists have a vested interest in understanding the long-term ecological role of Chaga, as the chopping off of wild Chaga may accelerate beetle and other blights with untold downstream impacts. This onslaught for short-term profit may inflict long-term ecological damage, though more research is needed to fully understand the scope and long-term impacts.