The modifiable areal unit problem of spatial heterogeneity of plant community in the transitional zone between oasis and desert using semivariance analysis

The modifiable areal unit problem has significant implications for ecological research that involve investigating and analyzing the spatial heterogeneity of plant community. In this paper, semivariance analysis was used to evaluate the spatial characteristics of plant community in the transitional zone between oasis and desert. The spatial structures of the plant community were characterized using exponent model variogram parameters, including nugget (C-0) range (A(0)) and sill (C-0+C). Two methods were employed to determine the scale effect of spatial heterogeneity. (1) A constant grain size (10x10 m(2)) and variational plot areas have been used to analyze spatial heterogeneity of the plant community. (2) The grain size was only changed to analyze spatial heterogeneity. In addition, the plot of 500x500 m(2) was clustered into nested units of different shapes and different directions to analyze zoning effect. Finally, using semivariance analysis, we obtained a suitable plot area and zoning approach to weaken the scale and zoning effects. The results showed that the effects of scale on different variogram parameters had significant difference. For example, C-0 and C-0+C were very sensitive at small scales, A(0) was influenced significantly by plot area at larger scales, and C-0 and A(0) were relatively sensitive to different zoning approaches. In order to get more representative characteristic of spatial heterogeneity of the plant community, the sampling area should be more than 200x200 m(2) for Nitraria sphaerocarpa populations, 100x100 m(2) for Reaumuria soongorica populations, and a grain size from 20x20 m(2) to 30x30 m(2) for both populations.