Record vole numbers raise risk of tree damage and vole fever

Vole populations have reached record levels in parts of Kainuu, increasing the risk of damage to forest seedlings and vole fever infections this winter, Yle reports.

The Natural Resources Institute Finland says vole numbers in Kainuu and North Ostrobothnia are at a peak in their multi-year cycle this autumn. Kainuu has exceptionally high numbers of both field voles and bank voles.

Populations have also grown significantly over the summer in south-western Finland and parts of Lapland. Voles remain scarce elsewhere in the country. Research professor Otso Huitu of the institute says regional differences are considerable. Population cycles have partly returned to a regular three-to-four-year pattern, but remain unpredictable in Forest Lapland. A vole peak is forecast for Upper Lapland next year.

The institute says the risk of vole damage to forest seedlings is significant in Kainuu this winter. Field voles eat and gnaw the bark of young trees beneath the snow. Bank voles chew the tops of conifers several metres above the ground and can destroy small seedlings entirely.

The institute advises forest owners to trap voles, protect tree trunks with guards and pack snow firmly around seedlings. Owners of plantations established last summer should consider taking out forest insurance that covers vole damage.

High bank vole numbers also increase the risk of vole fever as the animals move into residential areas in late autumn. The Puumala virus that causes the illness spreads through the air from dust contaminated with vole excretions. Infections are most commonly contracted in outbuildings such as woodsheds that voles can enter.

Bank voles that enter indoor spaces should be trapped as soon as possible. Their droppings should be cleaned with a damp cloth rather than a brush or vacuum cleaner.