Fluctuation ratio theory and the practice of grassland vegetation in the north farming-pastoral ecotones of China

Vegetation fluctuation is an important part of vegetation dynamics.The characters of vegetation fluctuation are quite different between the grassland community and the forestry community.Based on the meanings of ecology and statistics,the grassland vegetation fluctuation and its fluctuation ratio were defined,the fluctuation ratio was built at the first time,and the fluctuation coefficients were specified by the method of expert weighting.The grassland vegetation quantitative fluctuation and its fluctuation ratio between year 2002 and 2006 in Yanchi County,Ningxia of northwestern China,in the north farming-pastoral ecotones were studied.Resultsshowed that the biggest positive fluctuation ratio was 0.685,meaning the best vegetation growth during recent years,which was in 2003.While the most negative fluctuation ratio was-1.098,meaning the worst vegetation growth during this period,which was in 2005.