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1 Sorbonne Universités 2 LSCE - Laboratoire des Sciences du Climat et de l-Environnement Gif-sur-Yvette 3 CSIRO - Commonwealth Scientific and Industrial Research Organisation 4 Ecosystem Services and Management 5 Dept Biol 6 Lhasa Plateau Ecosystem Research Station, Key Laboratory of Ecosystem Network Observation and Modeling 7 State Key Laboratory of Vegetation and Environmental Change 8 GSFC - NASA Goddard Space Flight Center 9 Laboratoire de Météorologie Dynamique 10 Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences 11 LGGE - Laboratoire de glaciologie et géophysique de l-environnement 12 Key Laboratory of Alpine Ecology and Biodiversity 13 UAR 0233 Collège de Direction 14 Institute of Soil Science and Agrochemistry, Siberian Branch Russian Academy of Sciences

Abstract : Grassland management type grazed or mown and intensity intensive or extensive play a crucial role in the greenhouse gas balance and surface energy budget of this biome, both at field scale and at large spatial scale. However, global gridded historical information on grassland management intensity is not available. Combining modelled grass-biomass productivity with statistics of the grass-biomass demand by livestock, we reconstruct gridded maps of grassland management intensity from 1901 to 2012. These maps include the minimum area of managed vs. maximum area of unmanaged grasslands and the fraction of mown vs. grazed area at a resolution of 0.5° by 0.5°. The grass-biomass demand is derived from a livestock dataset for 2000, extended to cover the period 1901–2012. The grass-biomass supply i.e. forage grass from mown grassland and biomass grazed is simulated by the process-based model ORCHIDEE-GM driven by historical climate change, rising CO2 concentration, and changes in nitrogen fertilization. The global area of managed grassland obtained in this study increases from 6.1  ×  106 km2 in 1901 to 12.3  ×  106 km2 in 2000, although the expansion pathway varies between different regions. ORCHIDEE-GM also simulated augmentation in global mean productivity and herbage-use efficiency over managed grassland during the 20th century, indicating a general intensification of grassland management at global scale but with regional differences. The gridded grassland management intensity maps are model dependent because they depend on modelled productivity. Thus specific attention was given to the evaluation of modelled productivity against a series of observations from site-level net primary productivity NPP measurements to two global satellite products of gross primary productivity GPP MODIS-GPP and SIF data. Generally, ORCHIDEE-GM captures the spatial pattern, seasonal cycle, and interannual variability of grassland productivity at global scale well and thus is appropriate for global applications presented here.

Author: Jinfeng Chang - Philippe Ciais - Mario Herrero - Petr Havlik - Matteo Campioli - Xianzhou Zhang - Yongfei Bai - Nicolas Viovy - J



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