The taiga is the world’s largest terrestrial biome. In North America it covers most of inland Canada and Alaska as well as parts of the extreme northern continental United States(northern Minnesota through the Upper Peninsula of Michigan to Upstate New York and northern New England) and is known as the Northwoods. It also covers most ofSweden, Finland, much of Norway, lowland/coastal areas of Iceland, much of Russia from St. Petersburg in the west to the Pacific ocean (including much of Siberia), northernKazakhstan, northern Mongolia, and northern Japan (on the island of Hokkaidō). However, the main tree species, the length of the growing season and summer temperatures vary. For example, the taiga of North America consists of mainly spruces; Scandinavian and Finnish taiga consists of a mix of spruce, pines and birch; Russian taiga has spruces, pines and larches depending on the region, the Eastern Siberian taiga being a vast larch forest.
The term “boreal forest” is sometimes used (particularly in Canada but also in Scandinavia and Finland) to refer to the more southerly part of the biome, while the term taiga is often used to describe the more barren areas of the northernmost part of the taiga approaching the tree line and the tundra biome.
Taiga is the world’s largest land biome, and makes up 29% of the world’s forest cover. According to some sources, the boreal forest grades into a temperate mixed forest when mean annual temperature reaches about 3 °C. Discontinuous permafrost is found in areas with mean annual temperature below 0 °C, whilst in theDfd and Dwd climate zones continuous permafrost occurs and restricts growth to very shallow-rooted trees like Siberian larch. The winters, with average temperatures below freezing, last five to seven months. Temperatures vary from −54 °C to 30 °C (-65 °F to 86 °F) throughout the whole year. The summers, while short, are generally warm and humid. In much of the taiga, -20 °C would be a typical winter day temperature and 18 °C an average summer day.
Taiga soil tends to be young and poor in nutrients. It lacks the deep, organically enriched profile present in temperate deciduous forests. The thinness of the soil is due largely to the cold, which hinders the development of soil and the ease with which plants can use its nutrients. Fallen leaves and moss can remain on the forest floor for a long time in the cool, moist climate, which limits their organic contribution to the soil; acids fromevergreen needles further leach the soil, creating spodosol, also known as podzol. Since the soil is acidic due to the falling pine needles, the forest floor has only lichens and some mosses growing on it. In clearings in the forest and in areas with more boreal deciduous trees, there are more herbs and berries growing. Diversity of soil organisms in the boreal forest is high, comparable to the tropical rainforest.