Cervids and biodiversity in boreal forests

Kjell Danell

Department of Animal Ecology, Swedish University of Agricultural Sciences,
SE-901 83 Umeå, Sweden

During the last decades the populations of ungulates, especially moose and roe deer, have increased in Fennoscandia. There are several underlying factors behind this change. Forestry has created large young forests with plenty of food, the pressure from predators has declined, the winters have been more favourable and the cervid populations have been managed in order to increase the production of meat and trophies.

With the increase of the cervid populations there followed a significant increase in  damages to the forest trees, especially on Scots pine. Now there is also concerns on the negative impact on biodiversity and the long term production of the forest ecosystems. Similar trends are seen in e.g. central Europe and North America and the cervids have become a "hot" issue in nature conservation.

A common observation is that preferred browse species, i.e. rowan and aspen, are not allowed to grow above the browse line. Therefore, reproductive and full-grown trees become less abundant. Will these deciduous trees be exterminated? If so, a high number of red listed species of cryptogams and invertebrates that are highly dependent upon e.g. large aspen trees  will likewise be extinct.  

In order to better understand the impact, both negative and positive, of cervids on biodiversity we need a better understanding on how the different activities affect the species richness and the population sizes of rare and abundant plant and animal species, the habitat structure and composition, and the plant succession as well as the soil processes.

Often we study the responses of cervids by comparing plant and animal communities inside and outside exclosures. This gives us valuable information, but do not answer the question: How many cervids shall we have in order to balance positive and negative effects? Are there other methods?