Alpine tundra is another formation class that occurs above the treeline at high elevation, and resembles arctic tundra in appearance. Permafrost , permanently frozen soil, is present, and its upper layer melts in the summer creating marshy conditions over wide areas. Decomposition of dead plants is slow due to cold temperatures, so a thick organic layer of topsoil develops here. Tundra plants are small, and consist of sedges, grasses, mosses, lichens, forbs, and occasionally the dwarf willow, a very low shrub. Also found in higher elevations in some mountain ranges, like the Rocky Mountains.
Species are few , in fact, sometimes consisting of only one or two conifer species.
The shape of these trees helps minimize effects of heavy snowfalls. More commonly called the boreal forest , which mainly consists of white, red, and Engelmann spruce, and subalpine and balsam fir in North America, and European and Siberian larch and Scots pine in Eurasia. In northern Russia, this biome is called taiga . Some deciduous trees occur, like quaking aspen, willow, and birch, but minor, usually as pioneering species in land that has been cleared, perhaps due to fire. The boreal forests have been shown to be an important sink for excess carbon dioxide, and may mitigate effects of the increased greenhouse gases.