Analysis of spatial pattern and competition relationship of shrub community in arid desert of Western Ordos Plateau

The dominant shrub community(quadrat area 50 m×50 m)of Tetraena mongolica Maxim.,Sarcozygium xanthoxylon Bunge,Nitraria tangutorum Bobr.and Reaumuria songarica(Pall.) Maxim.in arid desert of Western Ordos Plateau was investigated,and four shrubs were divided into four shrub groups according to the root distribution depth(0-30,30-60,60-90 and 90 cm) in soil.Using functions of univariate g(t),markcorr(t) and bivariate g12(t),the spatial pattern and competition relationship among shrubs in four shrub groups were researched.The analysis results of g(t) and markcorr(t) functions show that the spatial pattern of shrubs in all four shrub groups almost is significant random distribution in 0-25 m scale,only that of shrubs with root distribution depth of 0-30 cm is uniform distribution in small scale(1 m).Except mark of the shrubs with root distribution depth more than 90 cm appearing more significantly negative correlation in 12-13 m scale,all marks among different shrub groups have no correlation in 0-25 m scale,which means that there is no obvious rejection among shrubs with similar root distribution depth,and individual size of shrubs is not affected by other shrub individuals around them.The analysis result of g12(t) function shows that except correlations between the shrub groups with root distribution depth of 0-30 and 30-60 cm and between those of 30-60 and 60-90 cm being significant in some meso-or small scales(3.0-3.5 m,1.5 m and 7.0-7.5 m),almost there are no significant interactions between any two shrub groups with contiguous root distribution depth in 0-25 m scale,which means the shrub individuals with different root distribution depths have no influence on each other.It is suggested that shrubs possessing different ecological characters occupy respective soil layers and stratify to use water and nutrient in soil,and have no competition to resources with each other in arid desert of Western Ordos Plateau.