Land-use change in the tropical savannah (Cerrado) of South America

Tropical grasslands of Latin America originally occu- pied more than 250 million ha of land and thus reached the same dimension as that of the global arе of irrigated arable land. However, during the last few decades, the grasslands of Latin America have been subjected to significant land-use changes in favour of arable land to produce cash crops such as soybeans, maize and sugarcane. During 1980–2000, the total grassland area halved, while soybean cultivation area increased by five times (FAOSTAT, 2012). Given the current situation on the world agricultural market, which is characterized by a high demand for cash crops, land-use change of grassland into arable land is likely to remain at high rates leading to an additional loss in area of 22 million ha by 2020 (Thomas et al., 2004). This trend implies a serious threat to the South American grassland biomes (Hecht, 2005), which cor- responds with an increase in soybean area expansion rates in the Cerrados of 935% between 1980 and 2006 (Souza et al., 2007). To protect grassland and rainforest ecosystems, different measures have been implemented in recent decades, such as designation of protection areas. Nevertheless, economic interests still prevail in the producing as well as in the consuming country (Brannstrom, 2009). Land-use-change-induced losses of forest and grass- land biomes not only threaten biodiversity but also imply further environmental burdens, such as deplet- ing soil organic carbon stocks or gaseous and water- borne nutrient losses. Both the depletion of soil organic carbon stocks and gaseous losses of nitrous oxide burden the GHG balance of soybean cultivation in South America. Brazilian scientists estimate that the ongoing land conversion of grassland into soybean-dri- ven arable cropping leads to an annual loss of soil organic matter of 2–4% (Zach et al., 2006). This implies further environmental impacts such as soil compaction, erosion and increasing application of pes- ticides to manage weeds, pests and diseases. A promis- ing way out of the land-use dilemma is provided by integrated production approaches (Dros, 2004). For instance, integrated soy–cattle systems, which include the cultivation of high-yielding tropical grasses, pro- vide much greater forage productivity than extensively used grasslands while preserving soil organic carbon. Therefore, integrated crop–livestock zero tillage sys- tems are considered promising for the sustainable intensification of the agricultural production in Brazil (Guimara ˜es et al., 2004). An important grass species in tropical forage systems is Brachiaria brizantha (Hochst. ex A. Rich) Stapf., a typical C4-grass with high water- and nitrogen-use efficiency. Digestibility of around 70% and pronounced root growth makes this grass a valuable forage plant and an important carbon source (Figure 6). Whether or not the intensified forage production in South America meets the criteria of sustainability is thus predominantly determined by the system applied. The interdependencies between environment and management system are also of great importance for the ecological assessment of the agricultural produc- tion in Europe. For instance, large quantities of South American soybeans and soybean meal are imported by the EU as a feed basis for the production of milk or meat. Therefore, environmental burdens, such as GHG emissions, associated with the cultivation of soybeans or the production of soybean meal are closely linked with the production of milk and meat in the EU; i.e. considerable amounts of soya-based feed from South America are imported to raise pigs, poultry, cattle and dairy cows. Thus, competition on the global meat market between South America and the EU has increased in the last decade. In total, the virtual net import of agricultural land into the EU accounts for 36 million ha (V. Witzke and Noleppa, 2010), predom- inantly through the import of South American soya. In this context, comparative life cycle assessments (LCA) (e.g. carbon footprinting) of milk or meat pro- duced in different regions of the world according to common criteria of sustainability are strongly demanded. However, in the context of the European debate on whether or not land-use change of native grasslands into intensified, integrated agroecosystems in South America (e.g. for exporting beef and soybean produc- tion) are tolerable, it should also be borne in mind that the area of native forest vegetation in Europe has decreased markedly during the last 5000 years, pre- dominantly induced by the land-use change from for- est to arable land. Expressed simply, the South Americans are just catching up with the land changes that Europeans began in the late Stone Age. Neverthe- less, there is an ongoing debate on how to assess the land-use change at different temporal and regional scales (e.g. Gerber et al., 2010; Hortenhuber et al., 2010; Flysjo et al., 2012; Zehetmeier et al., 2012). Soy- beans fed to dairy cows may have been harvested on areas that have recently been converted from grassland or forest into arable land, which needs to be assessed when evaluating sustainable intensification of dairy farming in Europe or elsewhere in the world.

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