内蒙古白音锡勒牧场区域尺度草地退化现状评价

采用双指示种分析(TwoW-ay Indicators Species Analysis,TWINSPAN)和无偏对应分析(Detrended Correspondence Analysis,DCA)对内蒙古白音锡勒牧场范围内32个草地植物群落样点的样方数据进行群落数量分析,根据数量分析结果将研究区草地划分为轻度、中度和重度退化3个不同等级。分析了单位面积草地地上生物量干重与退化等级的关系,在此基础上给出了划分草地不同退化等级的生物量判别指标值。利用2004年的TM遥感数据,结合同期地面植物群落样方调查,比较了不同植被指数与地上生物量和群落盖度的相关性,建立了研究区草地地上生物量估产模型,估算了白音锡勒牧场区域尺度草地地上生物量,结合不同草地退化等级的生物量判别指标值进行了草地植被退化空间分析。结果表明:①草地生物量与草地植物群落退化密切相关,一般草地退化越严重,群落生物量越低;②比值植被指数(R VI)与地上生物量干重相关性最好(R 2=0.644);③研究区轻度退化、中度退化和重度退化的草地面积分别占研究区总面积的24.51%、43.63%和24.12%。

Assessment on Grassland Degradation at Regional-scale in the Baiyinxile Ranch, Inner Mongolia

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.