Figure 8 Vegetation diversity indices at two scales:
Margalef, Pielou, Simpson and Shannon-Wiener indices.
The spatial distribution of diversity indices shows a gradual decrease
from east to west (Figure 8), influenced by species composition. The
eastern region with mixed shrub-grassland has high diversity values, the
middle region dominated by trees and shrubs has moderate values, and the
western region with shrubs like Artemisia and Salix has low values.
Salix possibly has a strong ability to occupy resources, which
suppresses the growth of other species. Additionally, its large canopy
limits the amount of sunlight reaching vegetation underneath its
branches and leaves, resulting in little nearby vegetation (Alvarez et
al., 2011; Pierce et al., 2019).
3.2.3 Spatial Autocorrelation
Analysis
Spatial autocorrelation analysis was conducted to examine the
distribution of vegetation diversity and to determine the presence of
clustering. The analysis showed that global Moran’s I index for each
diversity index was greater than 0, indicating clustering. Shannon index
had the highest global Moran’s I value among all indices. For example,
at two scales, the Moran scatter plots were mainly distributed in the
first and third quadrants with global Moran’s I indices of 0.469 and
0.463, respectively (Figure 9). Both were statistically significant at
the significance level of α=0.05 (z>1.96), indicating
strong positive spatial autocorrelation and significant spatial
clustering rather than random distribution in space. High-high
clustering was mainly located in the east of the study area,
corresponding to areas of high diversity. In contrast, low-low
clustering was mainly located in the west, corresponding to the
low-diversity region. High-low and low-high clustering were sporadically
distributed throughout the study area. These results demonstrate the
spatial distribution characteristics of clustering and differentiation
using the Shannon index.