Using a mixture of species in forest management has been common in Europe for the last three centuries. Hegre and Langhammer (1967) and Stewart et al. (2000) have presented overviews of the importance of mixed stands and their management in different countries worldwide.

In Finland and Norway, a forest stand is defined as being mixed if 20 % of its basal area is made up of broadleaved species, with conifers comprising the dominant species (Frivold, 1982). In Sweden, the proportion is 30 % and in Italy 10 % of the basal area. The Swedish definition of a mixed broadleaved and coniferous stand is "a type of stand in which the total percentage of broadleaved species is 30-70 % of the growing stock" (Anon., 2010). In Nordic countries mixed stands are the most frequent type of stand.

Mixed stands mostly establish spontaneously i. e. a planted or naturally regenerated conifer stand is mixed with naturally regenerated broadleaves. Areas of clear felling that are moist are readily colonized by broadleaves, which can establish from seeds, sprouts or suckers. The number of stems can amount to 5000 to 50,000 per hectare. However there is a conflict between broadleaf cover preventing frost damage to young spruce trees and the strong competition between broadleaves and conifer seedlings. In older stands, both species become established, competition is stabilized and the risk of frost damage declines (Johansson, 2003).

Mostly, Nordic forestry is focused on the management of stands for the production of softwood. A large number of young broadleaves are likely to compete with the conifer seedlings in such stands. In the past, the broadleaves were cut or treated with herbicides. Nowadays, with increasing interest in the supply of biomass for bioenergy production, other management systems have been introduced.

When managing mixed forest stands, a stratified mixture of shade-tolerant, late-successional species in the lower stratum and early successional species in the upper stratum is recommended (Assmann, 1970; Kelty, 1992). Mixed stands may contain alder, aspen or birch and Norway spruce (Johansson, 2003), (Fig. 4). The management of mixed stands is often based on stands which have not been cleaned at the correct time. The spontaneous establishment of broadleaved trees takes up to10 years.