Nutrient Cycling in Terrestrial Ecosystems

Volume 10 of the series Soil Biology pp 271-307

Dryland Ecosystems

  • Anne HartleyAffiliated withEnvironmental Studies Department, Florida International University
  • , Nichole BargerAffiliated withInstitute of Arctic and Alpine Research, University of Colorado, UCB 450
  • , Jayne BelnapAffiliated withU.S. Geological Survey
  • , Gregory S. OkinAffiliated withDepartment of Geography, University of California

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Drylands occupy approximately 40% of the Earth’s land surface and have low inputs of mean annual precipitation (P) relative to mean annual potential evapotranspirational (ET) losses (Millennium Ecosystem Assessment 2005). The United Nations Educational, Scientific and Cultural Organization (UNESCO 1979) proposed the following classification scheme for drylands: hyper-arid zone (P/ET <0.03), arid zone (P/ET 0.03–0.20), semi-arid zone (P/ET 0.20–0.05) and subhumid zone (P/ET 050–0.75). The majority of studies summarised in this chapter were conducted in arid and semi-arid zones with mean annual precipitation ≤300 mm.