Peat (turf) is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands, bogs, or mires. The peatland ecosystem is the most efficient carbon sink on the planet because peatland plants capture the CO₂ which is naturally released from the peat, thus maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m, which is the average depth of the boreal peatlands". One of the most common components is Sphagnum moss, although many other plants can contribute. Soils that contain mostly peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs flows of oxygen from the atmosphere, slowing rates of decomposition.