RESULTS
Beta diversity values
As shown in Table 2, the expected β-diversity of each plot at the
region, zone, area, district, and plot levels ranged between 0.332 and
0.684, 0.107 and 0.664, 0.046 and 0.694, 0.042 and 0.695, and 0.000 and
0.537, respectively. The mean values of the expected β-diversity
decreased as the pooling size decreasing from the regional to the plot
level. In addition, the observed β-diversity of each plot ranged between
0.000 and 0.737, and the mean value was found to be higher than the
expected β-diversity at the plot level.
Effects of the environmental filtering and spatial
aggregation
processes
As shown in Table 3, the effects of the environmental filtering at the
region-zone, zone-area, area-district, and district-plot scales were
0.077, 0.027, 0.019, and 0.189, respectively. The environmental
filtering effects at each spatial scale were all observed to be
significant. The effect of the spatial aggregation was 0.074 and found
to be significant at the within-plot scale. The change in the
β-diversity patterns (Figure 4) indicated that the magnitude of
ecological effects was the strongest at the district-plot scale,
followed by that at the region-zone and within-plot scales. The
comparison of ecological effects along the latitudinal gradients (Figure
5) showed that the environmental filtering effects at the region-zone
and area-district scales had significantly increased with increasing
latitude. In addition, the environmental filtering effects at the
district-plot scale, and the spatial aggregation effects at the
within-plot scale, decreased significantly with increasing latitudes.
Key factors of the environmental filtering
processes
At the region-zone, zone-area, area-district, and district-plot scales,
approximately 74%, 22%, 20%, and 33% of the environmental filtering
effects, respectively, could be explained by the climate variables and
plot attributes (Table 4). At all four scales, both the temperature and
precipitation factors significantly contributed to the environmental
filtering. Furthermore, the other climate variables and plot attributes
had contributed to the environmental filtering effects, including the
wind speed, elevation, and soil depth at the region-zone scale; solar
radiation, wind speed and litter thickness at the zone-area scale; solar
radiation and litter thickness at the area-district scale; and slope,
aspect and litter thickness at the district-plot scale.