| The number of plant individuals of plant populations is important to evaluate community dynamics as the fundamental ecological parameter in grassland community, but so far few studies have dealt with spatial pattern of the number of plant individuals in grassland. In addition, the power law model has been applied to analyze spatial heterogeneity based on the occurrence of plant, but the shortcoming of occurrence is that the quantitative description and accuracy are not satisfactory. Therefore we explore whether the power law model can be used to evaluate spatial heterogeneity of the number of plant individuals in grassland community, and compared the power law model and the negative model. Our objective is to explore whether the power law model is validity and high efficient to analyze the spatial heterogeneity of number of individuals of plant populations, and analysis the spatial pattern of plant populations and community.As reference data, surveys of individuals were conducted on a natural grassland and a weed community in Guanzhong Region of Shaanxi Province, following random sampling method using 100 0.5 m × 0.5 m quadrats. We recorded the number of plant individuals of each species occurring in each quadrat, in which counted the number of tillers of gramineae and cyperaceae plants, and counted independent individuals as the number of individuals of other species. We analyzed the spatial heterogeneity of plant populations and the whole community through established the power law model of the number of individuals, then deduced the formula to calculate out the spatial heterogeneity index value, and draw the line graph of the power law model. In addition, the analytic method and results were compared between the power law model and the negative binominal.Our results show that(1) In the line graph of power law model for all species in two plant communities, R2(coefficients determinant) of the regression line > 0.92, the regression residual(?i) of all species are close to zero, and the absolute value < 0.8. Therefore, the power law model fits well to the spatial pattern of number of individuals in plant populations.(2) The spatial heterogeneity index value of same plant population and community are different, When using power law model and negative binominal model to calculate that, but they have the tendency to positive correlation, and spatial pattern are consistent of every plant population and community, so the power law model can be applied to evaluate spatial pattern of the number of individuals of plant populations in grassland.(3) Correlation coefficient are-0.225 and 0.550 between the number of individuals of plant population and spatial heterogeneity index value in the negative binominal model, while, correlation coefficient are 0.712 and 0.925 in the power law model, and have a significant positive relationship(P < 0.01). so spatial heterogeneity index value in the power law model was more positively associated with average number of individuals of plant population.(4) The contribution value of plant population to spatial heterogeneity level of community are decided by the product of the number of individuals and spatial heterogeneity value of plant population.Therefore, the power law model can be applied to evaluate the spatial pattern of number of individuals in plant population on grassland, the power law model are more simple, convenient and reliable than the negative model, and it can intuitively analyze the spatial heterogeneity of number of plant individuals through the line diagram of power law model. In addition, the spatial heterogeneity index value and contribution value of each plant population to community increase with the number of individuals of plant populations. |
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