Special Column:Celebration of the 70th Anniversary of IGSNRR, CAS
FENG Xiu, TONG Chuan, ZHANG Lu, MIAO Bai-ling, DING Yong, ZHANG Yuan-ming
Grassland degradation is a major ecological problem in the Inner Mongolia region,because it causes drop of grassland productivity and leads to desertification.The objective of this study was to grade grassland degradation by using field quadrat data,and to assess the spatial extent and severity of grassland degradation using TM digital data in the Baiyinxile Ranch,which was the largest state-run ranch in Inner Mongolia. TWINSPAN(Two-Way Indicators Species Analysis,TWINSPAN)and DCA(Detrended Correspondence Analysis,DCA)were used to analyze the communities quatrat data of the 32 sample spots in the Baiyinxile Ranch,Inner Mongolia.The grassland in the study area was divided into three different degraded grades according to the results of quantitative analysis,and the relation between dry biomass per m2 and different degraded grades was proposed,and then the above ground biomass values for dividing the three degraded grades were developed.Using Landsat TM digital data in August 2004 and combining the investigation on grassland communities in the study area,the relations between the above ground biomass and RVI and NDVI were calculated,and the model of grassland above ground biomass estimation was established.The grassland degradation map was compiled by assessing the degraded grades of grassland in every pixel in the TM digital data,and the grassland above ground biomass at Ranch scale was estimated.The results indicate that:(1)there is a positive relation between the aboveground dry biomass and grassland degraded grades;2)the relation between the biomass and RVI was best(R2=0.644);and 3)the areas of slightly-degraded,moderately-degraded,and heavily-degraded grassland account for 24.51%,43.63% and 24.12% of the total study area. This study demonstrates the effectiveness of combining remote sensing data with field survey data in assessing grassland degradation in a regional scale,and provides useful information for improving grassland management and restoring the degraded grassland in the Baiyinxile Ranch.Grassland with different degraded grades needs different measures for their restoration.For the heavily-degraded grassland,the elimination of grazing by fencing may be necessary;for slightly-and moderately-degraded grassland,ecologically sound,advanced rangeland management measures,including grazing rotation,seasonal enclosures,and constructing artificial and semi-artificial grasslands should be considered.
