Spatio-Temporal Variation of Grassland in Western Songnen Plain

This paper analyzed temporal and spatial variation of various vegetation fractions and inner configuration of the grassland in western Songnen Plain where ecological environment was fragile based on the remote sensing data and classification of grassland resource with the support of GIS technology.It educes the quantities and characteristics of transformation among higher-coverage grassland,mid-coverage grassland,and lower-coverage grassland and other land use types from 1989 to 2001.The results indicate that the areas of three kinds of grassland are decreasing during 12 years.The transformation proportions to glebe are 77.78%,70.13% and 36.57% respectively,which illuminate that the main reason for the decrease of grassland is human's durative exploitation of grassland.The transformation proportion from grassland to saline-alkalized land increases with the decrease of grassland's vegetation fraction and is 0%,4.62%,and 32.81% for higher-coverage grassland,mid-coverage grassland and lower-coverage grassland,respectively.It shows that a crucial factor for saline-alkalized grassland is vegetation fraction.From the dynamic changing of grassland's inner configuration,we conclude that degenerative characteristic of grassland is from higher-coverage to mid-coverage and from mid-coverage to lower-coverage;moreover,the evolution is almost non-reversible under the current human activities.The degraded grassland is mostly located at the north of Zhenlai County,the south of Taonan City,the north of Tongyu County and the west of Qian'an County.Analysis of saline-alkalized grassland show that the most important reason causing saline-alkalized grassland is the continuous impact of human activities,and the status of mid-coverage grassland is the key affecting holistic quantity of grassland and the outspread speed of saline-alkalized grassland.Therefore,the only way for socio-economic and ecological environmental sustainable development is to utilize grassland resource soundly and restore the saline-alkalized grassland synthetically.At the end,the authors put forward the measures of ecological environmental restoration and grassland's sustainable development based on rational utilization of existing grassland resource and integrative prevention and rehabilitation of saline-alkalized grassland in research area.