The taiga is situated in between the tundra and temperate biomes and crosses the northern sections of North America and Eurasia. Also called the boreal forest, its landscapes are marked by coniferous trees, shrubs and moss and bodies of water such as lakes, rivers and bogs. The taiga's soils are not as fertile as those of tropical, subtropical or temperate biomes and thus cannot accommodate the same variety of vegetation. The taiga's harsh winters also influence soil characteristics.
The spodosol soil is not very fertile since it contains few nutrients and forms slowly, although it is home to coniferous trees. It is acidic because it is made mostly of decomposed conifer needles. The roots of conifers share a symbiotic relationship with a fungus that extends filaments to the soil's surface that attach to and break down the needles that have fallen off the trees. The top layer of spodosol soil is generally ash-gray in color. Below the layers are red due to the presense of iron and aluminum oxides.
Gelisols are found both in the tundra and taiga. In a gelisol soil type, permafrost is within 3 feet or less from the soil's surface. Generally, the top layer of gelisol soil is a dark gray followed by lighter to almost white horizons. Small water bodies and bogs tend to develop on top of the permafrost terrain since the water cannot seep through the frozen ground. Some vegetation survives in gelisols.
The Canadian Shield in North America and the Baltic Shield, in Norway, Sweden and Finland are both part of the taiga biome. They are composed of Precambrian and other ancient rock outcrops exposed at the surface. The Canadian Shield has a shallow layer of soil covering its igneous and bedrock structure. The Baltic Shield is composed of crystalline metamorphic rock and glacial sediments. Both are home to tree stands due to the presence of lakes, bogs and rivers.