Specialist species of wood‐inhabiting fungi struggle while generalists thrive in fragmented boreal forests

Summary The loss of suitable habitats is one of the main causes behind the loss of species and communities. Habitat fragmentation, that is, the division of the remaining habitat into small and isolated fragments, often co-occurs with the process of habitat loss. The spatial division of habitats decreases connectivity among local populations and generally has a negative effect on population viability, but it can also have a positive effect for some species, for example, due to released competition pressure. In both animals and plants, certain characteristics such as low dispersal ability and narrow ecological niche are known to be associated with fragmentation vulnerability, but in fungi, systematic analyses have so far been lacking. With their small and highly dispersive spores, fungi could be mainly resource-limited, not dispersal-limited. In this study, we analysed spatial occurrence data on 119 species of wood-inhabiting fungi to identify the species characteristics that are associated with high extinction risk and fragmentation vulnerability in particular. We modelled resource use and connectivity dependence separately for each species using the presence–absence data on 98 318 dead trees in 496 sites located on a gradient in the duration and intensity of land use in eastern Fennoscandia. We then related species' responses to connectivity to their resource-use patterns, life-history characteristics and red-list status. Our results show that red-listed species are highly specialized in their resource use and suffer from loss of connectivity at three spatial scales: along the large-scale gradient, at the landscape scale and at the scale of a forest stand. In contrast, many of the non-red-listed generalist species are actually more likely to occur (per resource unit) in fragmented managed forests than well-connected natural forests. Synthesis. We show that the expected number of red-listed species per a fixed amount of similar resources (dead trees) can be even more than 10 times higher in well-connected than in fragmented surroundings, and thus, protecting high-quality areas that are well connected is conservationally more effective than protecting small fragments distributed across the landscape.