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The term tundra is generally applied to treeless areas that are situated beyond the climatic limit for tree growth. This definition can denote both regions of high latitude north or south of the tree line (i.e. arctic/Antarctic or polar tundra), or high altitude belts above the natural tree line in all climatic zones (i.e. alpine tundra). Arctic and alpine tundras have many similarities, but also great differences. This chapter describes the processes of carbon (C) and nutrient cycling in arctic or arctic-alpine tundra, the latter referring to high elevation belts in the boreal region above 60 °N. The majority of this area is located in northern parts of Russia, North America and Scandinavia. For a comprehensive description of tundra systems, see Wielgolaski (1997).

Nutrient cycling in forests and to a lesser extent, in heathlands, has been regularly and thoroughly reviewed, especially in the past 15 or so years. For example, there have been numerous major projects, conferences and meetings focused on nutrient cycling in forests since 1990 (e.g. Boyle and Powers 2001; Nilsson et al. 1995; Schultze et al. 2000). These compendia are complemented by nutrient cycling contributions to more broadly based meetings (e.g. to Press et al. 1999). Seminal texts on biogeochemistry such as that by Schlesinger (1997) are essential reading and deal with forests, woodlands, shrublands and heathlands in varying detail. More recent works by Melillo et al. (2003), Schultze et al. (2001) and Vitousek (2005) are focused on biogeochemistry and global change. Even encyclopaedic treatments of aspects of nutrient cycling in forests are now available (e.g. Burley et al. 2005; Evans 2001).

Models evolve together with the evolution of our notion and perception of reality. Models can be narratives, graphical or mathematical descriptions, or computer simulations. More than two millennia ago, Chinese and Greek philosophers already had the notion that the environment was composed of the interacting elements earth, air, water, life and metals, but the complex relationships between these factors could only be understood after the birth of modern chemistry, at the end of the eighteenth century. The chemist Justus von Liebig (1803–1873) played an important role in unravelling how plants acquire nutrients from soil, air and water, but other chemists and microbiologists in the eighteenth and nineteenth centuries also contributed to improving the understanding of nutrient cycling processes (Smil 2001). Since that time, numerous (long-term) field experiments have been carried out to test Liebig’s mineral theory and its modifications. For over a century and a half, dose-response experiments have addressed one or more of the following five basic questions (Van Noordwijk 1999): (1) to what extent do nutrients limit crop yield and quality?; (2) what is the quantity of nutrients supplied by the soil?; (3) what constitutes an effective fertiliser?; (4) how much fertiliser should be applied?; and (5) what are the environmental consequences of fertiliser use?