Forest biodiversity in boreal Europe: Species richness and turnover among old-growth forests, managed forests and clearcut sites

Boreal Europe is a highly forested region, but a large proportion of its forests are managed for wood production. Consequently, clearcut sites are frequent, forest structures are modified, and the forest age distribution is truncated. Understanding the impacts of these habitat modifications on forest species assemblages is crucial for the maintenance of biodiversity. Here, we systematically reviewed published studies ( n = 99) that compared the species assemblages of three types of forests in boreal Europe, stratified based on age and management status: old-growth forests (>120 years old, unmanaged), managed forests (20–120 years old), and recently clearcut sites (<20 years old). We identified three main patterns: 1) The responses to habitat modifications induced by forest management varied considerably between taxa. The species richness of birds, epiphytic vegetation, wood-inhabiting fungi and saproxylic insects was higher in older forests. For understory vegetation, ground-dwelling invertebrates and non-saproxylic insects, species richness was higher in younger forests. No differences in species richness were found for soil fungi. 2) There was a high level of species turnover between clearcut sites and closed forests, i.e., they were inhabited by distinct sets of species. This applied to nearly all taxa. 3) Within closed forests, species richness increased with forest age or was higher in unmanaged forests, but some species groups were unaffected by the age of closed forests. The old-growth forests of boreal Europe are inhabited by unique species assemblages. As these forests are currently rare, the conservation of old-growth forests is crucial for maintaining forest biodiversity. • Species groups differed in their response to forest age and/or management. • There was a high level of species turnover between clearcut sites and closed forests. • Within closed forests, species richness increased with forest age.