Field guide to tree-related microhabitats. Descriptions and size limits for their inventory

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A habitat tree is defined as a tree bearing at least one tree-related microhabitat. A tree-related microhabitat (abbreviated as TreM) is a morphological feature present on a tree, which is used by sometimes highly specialised species during at least a part of their life cycle. These features may create shelters, breeding spots or crucial hibernating or feeding places for thousands of species. Various biotic or abiotic events can create tree-related microhabitats: for example, a falling rock could injure the bark, lightning could strike a tree and crack open the wood, or a woodpecker could dig a breeding cavity in the trunk. For some TreMs like vertebrate nests or witches’ broom, the tree is merely a physical support. Only morphological features that are known to have a direct link with one or more associated species are classified as TreMs.

To reinforce biodiversity in a stand and thus improve its resilience, it makes sense to know which tree-related microhabitats are present, and to preserve and favour them through adapted management practices.

This field guide describes 47 different tree-related microhabitats and classifies them into 15 groups and seven types. The guide also indicates recommended minimum inventorying sizes for each TreM and gives information about its frequency of occurrence and its replacement rate in the stand.