Short-term responses of a Stipa grandis/Leymus chinensis community to frequent defoliation in the semi-arid grasslands of Inner Mongolia, China.

摘要

Grassland degradation due to over-grazing causes severe ecological and economical problems in the semi-arid grasslands of Inner Mongolia, PR China. The development of sustainable management systems is required, but basic information regarding the degradation process in its formation and development is rare. In 2004 and 2005 a cutting-frequency experiment was conducted in the Xilin River Basin, Inner Mongolia, subjecting a non-degraded grassland area to 3 different cutting frequencies: single defoliation at the end of growing season and defoliations every 6 and 3 weeks. It was hypothesised that the productivity of the S. grandis/L. chinensis community will be reduced by frequent defoliations. The cumulative dry matter yield increased with increasing defoliation frequency from 204 to 277 g DM m-2 in 2004 and from 87 to 158 g DM m-2 in 2005. The low aboveground biomass productivity in 2005 resulted from the low amount of precipitation, which was only 50% of the long-term mean. The nitrogen yield increased from 2.9 to 6 g N m-2 in the frequently defoliated treatments in 2004 and from 1.2 to 2.8 g N m-2 in 2005. Total leaf area was significantly reduced by frequent defoliation, but specific leaf area increased both in S. grandis and L. chinensis. Root mass (0-15 cm) was on average 929 g OM m-2 in 2004 and 882 g OM m-2 in 2005 and, as well as species composition, not significantly influenced by frequent defoliations. It was concluded that frequent defoliation positively affected the productivity of the S. grandis/L. chinensis community, and that the annual amount of precipitation essentially determined the biomass production of this grassland ecosystem. Because the community increased its productivity after frequent defoliation in the 2 experimental years, it was suggested that the community is resistant to defoliation stress in the short-term.