Research on Spatial-temporal Dynamics and Landscape Pattern Change of Grassland in Songnen Plain

Grassland had heavily degraded in Songnen Plain,and it is important to maintain balance of ecosystem by studying on spatial-temporal dynamics and change of landscape pattern of grassland.Based on RS and GIS technique,three-period(1986,1995,2000) remote sensing images were interpreted to extract spatial information of grassland landscape in the region,and spatial-temporal dynamics of grassland and change of landscape pattern were analyzed.The results showed that grassland area decreased by 25.6%,grassland degradation is serious.Patch number of grassland decreased by 18.38%,and degree of fragmentation is enhanced,patch shape changed little.During 1986~1995,low coverage grassland rapidly developed,and high coverage grassland fast declined during 1995~2000,and it actively contributes to decrease of grassland.Grassland is mainly converted into cropland and saline-alkalized land,conversion area reaches 1116219.53hm~2 and 313708.75hm~2,respectively.From 1986 to 2000,centroids of various grasslands moved towards northeast direction,and in different stages,centroids change of each kind of grassland are irregular and multi-directional.Both natural factors and human activities result in grassland degradation in the studying region,natural factors are basic condition of grassland degradation,and human activities are crucial factors.