Forest damage caused by the Canadian beaver (Castor canadensis) in South Savo, Finland

Abstract

1999. Forest damage caused by the Canadian beaver ( Castor canadensis ) inSouth Savo, Finland. Silva Fennica 33(4): 247–259.The increasing Canadian beaver (Castor canadensis) population has caused forestdamage in Finland. However, the occurrence, extent and importance of the damage havenot been comprehensively studied. The field inspection was carried out in all of thebeaver damage areas (n = 50) in the Anttola, Juva and Pieksamaki game managementunits in summer 1998. The characteristics of the damage areas, types of damage and theseverity of the damage were examined. The size of the damage areas averaged 2.2 ha.The damage areas occurred on peatland forest more (p < 0.05) than expected. Thedominant tree species were commercially valuable trees such as Scots pine (Pinussylvestris) (33 %), Norway spruce (Picea abies) (18 %) and birches (Betula spp.) (47%). Birch occurred as dominant tree species more (p < 0.05) than expected. Theproportion of older forest development classes was considerable. The most importanttype of damage was flooding (50 %) caused by the damming activity of beavers. Thetrees were dead or dying in 18 % of the damage areas. It was estimated that theecosystem engineering performed by beavers was of no importance in 28 % of thedamage areas. Prevention of beaver damage has been carried out in 80 % of the damageareas. In the study area, beaver numbers have steadily increased, although the number ofbeavers taken by hunting and the allowed hunting harvest have sharply increased. It issuggested that the methods used to prevent beaver damage should be improved and acompensation system should be provided by the state for the most damaged areas.Beavers can cause damage to commercial forestry, and this should be taken into accountmore effectively in the management plans made by the game management districts.