Voles can cause considerable damage in young forests and in gardens. Most of the damage occurs during the winter in peak population years. Vole populations typically fluctuate in 3–4-year cycles.
At times voles can cause more damage than moose and deer. The biggest vole population boom of all time in southern Finland was recorded in the winter of 2008/2009, when voles destroyed approximately 20,000 hectares of young forest. Less severe damage occurred across an area approximately three times larger. The economic impact of the damage exceeded EUR 20 million.
There are 11 species of voles in Finland. The two most common and most pestilent are the field vole and the bank vole. Water voles, which spend the winter in underground burrows, can cause local damage to roots in soft soil. Field voles usually operate under snow, where they gnaw at the base of plants. Bank voles, on the other hand, readily climb up the seedlings of coniferous trees to feed on the terminal buds and the bark on the tree crown.
Research to reduce damage to seedlings
The Natural Resources Institute Finland conducts extensive research on vole population fluctuations, factors that contribute to vole damage, forest management practices aimed at minimising the risk to seedlings, and the recovery of seedlings after a vole attack. We also study and develop repellents to protect seedlings. Ground cover prevention, the choice of tree species, the origin and size of seedlings, the fertilisers used in the nursery, and the time of planting can all have an effect on the scale of vole damage.
The Natural Resources Institute Finland carries out research in collaboration with various Finnish and international research organisations and universities. Cooperation with practical operators is also important.
Vole inventories to support forest management planning
Carrying out national inventories on the fluctuation of vole populations is a statutory duty of the Natural Resources Institute Finland. The results of vole inventories are published twice a year. The objective is to help customers, especially forest owners, to identify times when the risk of damage to seedlings is the highest and to plan their planting schedule accordingly. Research on vole damage produces detailed information for customers on forest management practices that help to minimise and mitigate vole damage.
Picture on top of the page: Erkki Oksanen, Luke