A heart-rot fungus, Inonotus obliquus (chaga), mediates microhabitat creation in birch snags and contributes to forest fungal diversity

Ecological significance of fungi in terrestrial ecosystems is generally acknowledged but the ecological networks mediated by particular fungal species are seldom described. In this note, we draw attention to an undescribed function of a well-known heart-rot fungus, Inonotus obliquus (chaga). This species mostly inhabits live birches (Betula), where it forms sterile conks used in ethnomedicine. Less known is that its short-lived fruit-bodies develop under the bark after the tree death and release the spores by cracking the bark. Based on studies in Estonia, we report that this process is a major mechanism that removes bark from standing dead birches and that the exposed wood becomes a distinct woody substrate. We report nearly 50 species of epixylic lichens and allied fungi on birch snags, most notably calicioid fungi, which include several species of conservation concern. Because forest management suppresses that stage through multiple mechanisms (removal of trees with conks and dead trees; shortened rotations; preference for conifer monocultures), the keystone function can be lost even if I. obliquus persists in the area. Additionally, multi-functional forestry that supports chaga for its conk use should pay attention to that later phase of fruit-body formation to maintain natural functioning of this species. Such microhabitat providing functions may be more widespread among fungi that currently acknowledged.