By now China is one of the countries facing the most serious desertification problems in the world. The total area affected by desertification is approximately 2.6 million km2 , covering 27.3% of total territory of China. Increasing stocking rate exacerbated the extensive degradation of grasslands in Inner Mongolia accompanied by increased soil erosion and desertification. Since grasslands represent one of the largest stocks for organic carbon, its degradation has a significant feedback on the biosphere-atmosphere exchange for carbon and nitrogen. Hence grassland degradation leads to volatilization and dislocation by erosion of huge amounts of C and N previously stored in this ecosystems.
The MAGIM Research Unit, funded by the German Science Foundation (DFG), with its 11 subprojects compares four differently managed grasslands, two ungrazed since 1999 and 1979, respectively, and two moderately and heavily grazed in the Xilin river catchment in Inner Mongolia, PR China. At these experimental sites the C and N pools in the soil (P1), the above- and belowground net primary production (P2), C and N turnover and fluxes (P5), carbon and water exchange (P6), the water balance (P7), soil stability (P8), and wind erosion (P9) are studied. P3 and 4 investigate biomass availability, fodder uptake and quality and animal productivity in a newly established experiment with five different grazing intensities and two management strategies (continuous grazing and hay making versus rotation). P10 and 11 work on a larger scale: P10 analyzes the influence of grazing pressure on the carbon isotope composition of the grasslands, and P11 tries to infer rain rates within the Xilin catchment with surface and satellite based remote sensing.
In the scope of the MAGIM project the validity of the following main hypotheses will be tested:
- Intensive grazing replaces slow growing plant species, and affects abundance of C 4 species.
- Differences in productivity of plant communities are related to differences in water use efficiency.
- Overgrazing leads to a reduced belowground C input in grassland soils, which in turn leads to a decline of soil organic carbon and increases gaseous volatilisation/emissions.
- Overgrazing affects soil bulk density, crusting, aggregation and infiltration capacity with major effects on the soil water balance. Due to increased runoff and reduced groundwater recharge, overgrazing reduces water availability.
- Overgrazing destroys plant cover and soil aggregates, inducing wind erosion (P8 and P9). Wind erosion is the major process of nutrient dislocation in the study area.
- Grazing intensity and management (continuos, rotational) are key factors for persistence and productivity of the sward.
- Parameters of growth analysis (tiller density, leaf area index) as well as the chemical composition (WSC) of sward dominating species can be used as indicators for the stability of the plant community.
- Long-term high animal productivity is not in conflict to ecosystem stability of grasslands.