Studies On Fine-scale Spatial Pattern Of Agropyron Mongolicum Population In Desert Steppe In Ningxia

In order to study the ecological process and environmental plasticity mechanism of Agropyron mongolicum population.The desert steppe which dominated by A.mongolicum in Yanchi,Ningxia was selected as investigative plots by using the method combining of point pattern analysis and geostatistics analysis.The plant structure,the spatial distribution pattern and association of intraspecific and interspecific in the fine scales were studied.The spatial characteristics of A.mongolicum population and the geographical factors in the heterogeneous habitat,the effects of different sampling scale and zoning approaches were discussed.The results were as follows:The proportion of 0-5 cm and 5.1-10 cm clusters were significantly higher than those of 15-20 cm and more than 20 cm clusters in A.mongolicum population,accounting for 79.24%of the total population.The population had adequate regenerative seedlings and exhibited good development trend in the 10 mx 10 m sample plot.The 0-15 cm clusters mainly aggregated at a small spatial scale(less than 4 m),and the aggregation degree strengthened with the decrease of individual size.As the scale increased,the aggregation degree decreased and gradually transformed to random and uniform distribution.The clusters larger than 15 cm of A.mongolicum appeared as random distribution at all scales.The association within 0-15 cm cluster degrees of A.mongolicum showed significant positive relationship at a small scale(less than 4 m),and tended to be unassociated with the increase of the scale.The remaining cluster levels showed no association at the 0-5 m scale.The A.mongolicum population mainly appeared as aggregated distribution in different communities,with the aggregation scale of less than 4 m.As the scale increased,the aggregation degree decreased and gradually transformed to random and uniform distribution.The associations between A.mongolicum and Stipa breviflora population,A.mongolicum and Lespedeza potaninii population showed significant negative relationship at a small scale(less than 4 m)and tended to be unassociated with the increase of the scale;and it showed no association between A.mongolicum and Cynanchum komarovii population at the 0-5 m scale.Soil total potassium showed weak variation;the soil water content,organic carbon,total nitrogen,total phosphorus,and the coverage and aboveground biomass of A.mongolicum population showed moderate variation in the investigative plot.The soil total nitrogen,organic carbon and water content showed strong spatial dependence,in which the structural factors had a dominant function.The soil total phosphorus,total potassium,and the coverage and aboveground biomass of A.mongolicum population showed moderate spatial dependence,which affected by the structural factors and random factors.The coverage and aboveground biomass of A.mongolicum population presented an irregular patchy distribution in the study area,which increased from southeast to northwest.The spatial distribution patterns were more similar to the soil water content.The spatial variation of A.mongolicum population were significantly influenced by sampling scale and zoning approach.In order to get more representative vegetation information of spatial heterogeneity,the sampling area should be more than 60 m×100 m for A.mongolicum population.