The class Vaccinio-Piceetea comprises coniferous forests (taiga) of the Eurasian, and maybe also North American, boreal zone and the montane belt of temperate mountains. These forests are typical of areas with cold winters and short growing seasons. In Europe the tree layer consists of species of Abies, Larix, Picea or Pinus, but it is often monospecific in particular stands. In places small-leaved angiosperm trees such as Betula spp., Populus tremula and Sorbus aucuparia can be scattered in the subcanopy, especially in post-disturbance stands. Betula can also dominate on organic soils such as at peatland margins. The herb layer is usually poor in vascular plants, containing species of boreo-continental distribution such as the dwarf shrubs Vaccinium myrtillus and V. vitis-idaea and various herbs and grasses. The moss layer is well developed, rich in species and attains high cover values. Soils are usually acidic and nutrient-poor, with a thick layer of poorly decomposed humus.