A dark soil with a thick, peat layer of poorly decomposed vegetation, which is usually underlain by a frozen layer of soil. Translocation is limited and there is, therefore, little development of horizons. Tundra soils range from brown earths in the more humid areas to polar desert soils in arid areas. Climate change may cause tundra soil to dry—accelerating oxygen uptake and hence heterotrophic respiration, which would result in increased CO₂ and methane emissions (Grant et al. (2003) Glob. Change Biol. 9, 1).