Fig. 3 Population density difference diagrams of Cleistogenes
songorica at different grazing intensities and spatial scales. Mean
values (±SD ; n = 24) of density. Different lowercase
letters indicate that grand means differ significantly between the
grazing treatments (P < 0.05). (1) 5 cm×5 cm; (2) 10
cm×10 cm; (3) 20 cm×20 cm; (4) 25 cm×25 cm; (5) 50 cm×50 cm; (6) 100
cm×100 cm.
Inter-specific association between Stipa breviflora andCleistogenes songorica populations
It can be seen from the Jaccard index (Table 3) of S. brevifloraand C. songorica populations that the value of Jaccard index
under grazing treatment was greater than that under non-grazing
treatment at different scales, indicating that grazing does increase the
inter-specific affinity of S. breviflora and C. songorica .
When comparing two sites under the same grazing intensity, we observed
that the value of the Jaccard index increased as our sampling sized
increased, implying an increase in the inter-specific affinity. At the
spatial scale of 5 cm×5 cm, the Jaccard index showed a strong
inter-specific competition between S. breviflora and C.
songorica . At the spatial scale of 100 cm×100 cm, we observed the
highest compatibility between S. breviflora and C.
songorica under grazing. At this scale, it appears that grazing
intensity has little effect the relationship between these grass
species. With the increase of grazing intensity, the inter-specific
affinity between the two species increased. Notably, we observed that
the influence of grazing on inter-specific affinity was greatest at the
smallest sampling resolution, and generally decreased as sampling
resolution was increasingly coarse. In summary, grazing increased the
inter-specific relationship affinity (competitive ability decreased)
between S. breviflora and C. songorica in order to resist
grazing disturbance, and this affinity was particularly prominent in
large scale.
Table 3 Jaccard index of Stipa breviflora and Cleistogenes
songorica populations