呼伦贝尔草原MODIS NDVI的时空变化特征

基于2000—2008年的MODIS NDVI数据，研究了呼伦贝尔草原4种主要草原类型（低地草甸、温性草原、温性草甸草原和山地草甸）年NDVI_max的空间变化趋势、波动程度、出现时间.结果表明：2000—2008年，呼伦贝尔草原植被趋于恶化的形势较严峻；研究区类草原NDVI_max平均值的年际波动明显，特别是温性草原NDVI_max平均值的年际最大波动接近50%；在各等级草原面积的变化上，尽管NDVI_max在(0.4,1］之间的草原平均面积约占研究区总面积的91%，说明呼伦贝尔草原植被状况总体较好，但NDVI_max值在(0.2,0.4]、(0.8,1］之间的草原面积趋于减少，NDVI_max在(0.4,0.8］之间的中高盖度草原面积趋于增加，总体形势不容乐观；66.25%的研究区草原植被状况趋于恶化，33.75%趋于好转；62.85%研究区的NDVI_max出现在每年第193天至第225天（即7月中旬至8月初），该时期是呼伦贝尔草原植被最重要的生长季节.

Spatiotemporal characteristics of MODIS NDVI in Hulunber Grassland

Time-series MODIS NDVI datasets from 2000 to 2008 were used to study the spatial change trend,fluctuation degree,and occurrence time of the annual NDVI_(max) of four typical grassland types,i.e.,lowland meadow,temperate steppe,temperate meadow steppe,and upland meadow,in Hulunber Grassland.In 2000-2008,the vegetation in Hulunber Grassland presented an obvious deterioration trend.The mean annual NDVI_(max) of the four grassland types had a great fluctuation,especially in temperate steppe where the maximum change in the mean value of annual NDVI_(max) approximated to 50%.As for the area change of different grade grasslands,the areas with NDVI_(max) between 0.4 and 1 accounted for about 91% of the total grassland area,which suggested the good vegetation coverage in the Grassland.However,though the areas with NDVI_(max) values in(0.4,0.8]showed an increasing trend,the areas with NDVI_(max) values in(0.2,0.4]and(0.8,1]decreased greatly in the study period.Overall,the deteriorating grassland took up about66.25 % of the total area,and the restoring grassland took the rest.There was about 62.85 % of the grassland whose NDVI_(max) occurred between the 193rd day and the 225th day in each year,indicating that this period was the most important vegetation growth season in Hulunber Grassland.