Study On Vegetation Characteristics Of Elm Sparse Forest Grassland In The Southern Margin Of Hunshandake Sandy Land

Ulmus pumila sparse forest in Hunshandake sandy land is a kind of super-zonal top community vegetation developed on sandy parent soil.It plays an extremely important role in social economy and ecological value of sandy area.Taking Ulmus pumila community in sandy land as the research object,this paper divides Ulmus pumila sparse forest in the southern margin of Hunshandake sandy land into three site types,i.e.interdune lowland,leeward slope and windward slope.The vegetation characteristics,spatial pattern and the relationship between vegetation and environmental factors of Ulmus pumila sparse forest in Hunshandake sandy land were studied.The community structure characteristics were analyzed by correlation analysis,variance analysis,multiple comparison and other statistical methods.The main results were as follows:(1)Among the three site types,the indexes(average DBH,average plant height and average crown width)of Ulmus pumila are the highest in the hilly lowlands,and the hilly lowlands are the best habitats for the growth of Ulmus pumila.The age structure of Ulmus pumila population in different habitats is typical pot-shaped,the population regeneration is poor,and there is a gradual decline trend;Caragana microphylla and Spiraea trifida are distributed in all three site types,while Salix minor and Salix yellow grow mainly in the hilly lowlands and leeward slopes,and the hilly lowlands are still the habitats suitable for most shrubs.(2)Ulmus pumila was aggregated on small scale in three site types.With the increase of age and scale,it showed a pattern of random distribution.Shrubs were aggregated on the whole.In three site types,the spatial correlation between young trees and middle trees was very small.There was a negative spatial correlation between young trees and mature trees,middle-aged trees and mature trees on medium and small scale,but not between shrubs.The spatial correlation between elm and shrubs is different,which is mainly determined by the physiological and ecological characteristics of shrubs themselves.(3)Among the three site types,the species diversity of shrub layer was inter-hill lowland>leeward slope>windward slope,herb layer species diversity was leeward slope>inter-hill lowland>windward slope,Pielou index of shrub layer and herb layer had no significant difference.Soil nutrient content of three site types was inter-hill lowland>leeward slope>windward slope,and soil PH had no significant difference among the three site types.Water is a limiting factor for vegetation growth in Hunshandake sandy land.