While many claim otherwise, from the data that we’ve seen it definitely looks to be sustainable.
The only sustainability report that we’ve found was done in Russia, which is done by a large exporter of Chaga. It showed that Chaga could easily sustain existing demand for the foreseeable future.
It also estimated that 20% of all birch forest in Russia are infected with Chaga.
The Finnish Forest Research Institute has said that anywhere from 6-30% of birch forests in Sweden and Finland are infected with Chaga.
Our own personal take is that Chaga is definitely sustainable as there are vast birch forests all across the northern hemisphere. The problem being that harvesters will have to go further and further into the woods to find Chaga which will further increase the price of raw Chaga. At some time, there may be a tipping point where Chaga will become too expensive for supplements which will curb demand well before there is any worry about over-harvesting.