Monitoring and conservation of endangered Siberian flying squirrel (Pteromys volans) populations – Implications for sustainable forest management.

In this thesis, I focused on the endangered Siberian flying squirrel (Pteromys volans) and its habitats, which are under pressure from widespread forest clear-cutting in Finland. I used long-term capture-recapture data from nest-box populations of the flying squirrel, in Western Finland. I studied variation in population size and demographic rates focusing on the impacts of habitat destruction caused by forestry and environmental factors 1993-2018.

In 25 years, 76.4% of the breeding habitat in my study area in Luoto was lost due to clear-cutting. The flying squirrel population size declined towards the middle of the study and increased again in the latter half of the study but was constantly clearly below the carrying capacity. Yearly survival rates were rather low (0.43-0.48). In Luoto, survival of females declined towards the middle of the study but increased towards the end of the study suggesting a major contribution of survival to the population growth rate. Annual variation in survival was linked to predation risk and climatic conditions. Importantly, survival increased with breeding habitat patch size until about 4-6 ha in size. Population recovery was associated with females crowding into larger breeding habitat patches with larger nest site resources. On the national level occurrence of flying squirrels decreased 36,9% between 2006 and 2017.

The second part of my thesis examines habitat requirements of the flying squirrel. I demonstrate that environmental authority conservation practices were inefficient in protecting breeding sites and resting places of flying squirrels. Areas with breeding sites where forests were cut according to guidelines failed to support flying squirrels, whereas occupancy of flying squirrels remained unchanged in untouched areas. Occupancy of flying squirrels increased strongly with the amount of suitable habitat and patch size, which is in line with the patch size effect on survival. This illustrates that the delineated areas of 0.07-0.24 ha were far too small to support breeding flying squirrels. Since 2016 it has been impossible to monitor protection of breeding sites from forestry as no delineations are made by the authorities and stakeholders have no possibility to evaluate the conservation efficiency.

The patch size of breeding habitat used by flying squirrels decreased strongly over the course of the study. In the latter years, occupied patches were on average 3.91 ha whereas unoccupied were 1.49 ha. These results warrant radical changes in the legislation regarding forestry practices if we are to maintain flying squirrel populations. Currently, breeding habitat for the flying squirrel is rapidly disappearing and fragmentation in my study area has reached an alarming level as the median size of remaining breeding habitat patches is only 1,5 ha. There is an actual risk that all of the breeding habitat can be clear-cut in the near future.

Keywords: Biodiversity, Endangered species, Forestry impact, Habitat destruction, Ecocide, Habitats Directive, Legislative protection, Pteromys volans, Survival, Science-policy gap.