Peat is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. It is the surface organic layer of a soil that consists of partially decomposed organic matter, derived mostly from plant material, which has accumulated under conditions of waterlogging, oxygen deficiency, high acidity, and nutrient deficiency. Peat is formed mainly from bryophytes (mostly sphagnum mosses), herbs, shrubs, and small trees in temperate, boreal, and sub-arctic regions, where low temperatures reduce the rate of decomposition. Peat moss, also called sphagnum moss, is one of the most common components in peat. Peat is used by gardeners and for horticulture in certain parts of the world, but this is being banned in some places due to environmental concerns. By volume, there are about 4 trillion cubic meters of peat in the world. Over time, the formation of peat is often the first step in the geological formation of fossil fuels such as coal, particularly low-grade coal such as lignite.