[Spatial pattern of two dominant shrub populations at transitional zone between oasis and desert of Heihe River...

Based on the field investigation in a 500 m x 500 m plot and applying geo-statistical theory and methods, this paper described the spatial pattern of the coverage, density, height and volume of two shrub populations Nitraria sphaerocarpa and Reaumuria soongorica at the transitional zone between oasis and desert of Heihe River Basin. The average coverage of the two populations was 1.56 +/- 2.34% and 0.23 +/- 0.22%, and their average density was 1.5 +/- 1.8 clump x 100 m(-2) and 2.3 +/- 2.1 individual x 100 m(-2), respectively. The height of N. sphaerocarpa was 0.18 +/- 0.15 m, and its volume 0.10 +/- 0.18 m3. N. sphaerocarpa population exhibited strip distribution pattern, while R. soongorica population showed uniform distribution pattern. The nugget (c0)/sill (c0 + c) ratio of the semivariogram of the two populations was 0.08-0.12, which indicates that the random variance of spatial heterogeneity occupied 8%-12%. In semivariogram model, the range value (A0) of the coverage and density was 14.7 and 33.9 m for N. sphaerocarpa, and 25.2 m and 24.9 m for R. soongorica, respectively. As a whole, the random spatial heterogeneity existed at the scale of 10 m, and autocorrelated spatial heterogeneity existed at the scale of 34 m. The spatial heterogeneity of the coverage and density of the two dominant populations showed both isotropy and anisotropy, and the isotropy scope of R. soongorica population was larger than that of N. sphaerocarpa. The spatial pattern of N. sphaerocarpa population was controlled by two factors. The first was precipitation and surface runoff, and the second was oasisofication and desertification.