PARENT SESSION
Symposium 17: Biogeochemistry of Grassland and Shrubland Ecosystems: Local to Regional Linkages and Impacts of Land Use
Organized by: R Nowak and S Fuhlendorf
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Chatham Ballroom B.

Global role of rangelands in biogeochemical cycles.

Schlesinger, William^*,1, ¹ Nicholas School of the Environment and Earth Sciences, Durham, NC, USA

ABSTRACT- Arid and semiarid systems cover nearly 30% of the Earth's land surface and harbor nearly 20% of the human population. Many of these lands are used for grazing and managed as "rangeland." Not contributing a large fraction to global NPP, soil carbon sequestration, or nitrogen cycling, can arid lands be ignored in studies of global biogeochemistry? Studies of past changes in the transport of dust to the polar ice caps indicate that the signature of arid lands on global function has varied widely-with large transports of dust at the Last Glacial Maximum affecting planetary albedo, ocean productivity, and the transport of loess and soil microorganisms to distant lands. Model predictions of transient mid-continental drought with global warming compel us to understand local biogeochemical processes in deserts, to predict how they might change in the future. Studies in the Jornada Basin (LTER) in southern New Mexico and other sites in the arid Southwest show that the biogeochemistry in deserts is often determined by the distribution of the sparse plant cover-with semiarid grasslands showing a relatively uniform distribution of soil nutrients in contrast to a patchy distribution in associated with vegetation in shrublands. Nutrient losses by erosion are greater in shrubland habitats. However, when semiarid grasslands are lost in favor of desertified shrublands, the total nutrient pool in the landscape shows relatively little change. Rather, desertification is associated with a redistribution of soil nutrients on the landscape. Future studies of biogeochemistry in arid habitats should focus on the episodic removal of soil fertility by wind erosion.

Key words: Biogeochemistry, Desertification, Arid lands