Forests with many different tree species or with a blend of different biotopes are called mixed forests. Mixed forests exist in infinite variations with no exact definitions and can contain both conifers and broadleaf deciduous trees.
Today man decides which species the forests contains and how they grow; most forests in Sweden are the result of forestry activities during the 20th century. Natural forests, not affected by mans activities, are called primary or virgin forests.
The composition of a natural forest depends on local climate and environment. On dry land we find pine forests mixed with some oak, birch, aspen and sallow. More fertile soils are dominated by the big broadleaf trees, oak, elm, linden, sometimes also spruce. Elder and ash prefer wet soils.
In Sweden there are but a few virgin type forests left. Natural forests, rich in species and with many old trees, growing as well as dead ones, are of great importance for endangered species of plants and insects. 23% of Sweden’s forests are mixed forests, according to the Swedish national forest inventory.