3 Results

3.1 Changes in population structure ofS. moorcroftiana under different topographies

The population coverage, plant height and CPA in different topography had obvious difference (Table 3). The mean coverage of these S. moorcroftiana populations was 58%, 34% and 30% in T1, T2 and T3, respectively. For different topography, T2 had the maximum mean height of 0.74 m and largest mean CPA of 4.13 m2, respectively. The plant heights followed the order of T2 (0.74 m) > T3 (0.54 m) > T1 (0.43 m), while there was no significant difference between T1 and T3 for CPA value. The total number of individuals was decreasing trend along T1 (2750), T2 (1475) and T3 (554). However, the height distribution structure in different topography was consistent (Fig. 3). The distribution of height classes followed the normal distribution curve (p < 0.001) and the class 2 of (0.3-0.6) m was most prominent in all survey plots. The percent of class 2 reached to 83.2%, 80.5% and 89.2% in T1, T2 and T3, respectively. The class 1 reached to 13.9 % in T1 and the class 3 reached to 13.7 % in T2. The significant linear positive correlation (p < 0.01) was shown between height and CPA of eachS. moorcroftiana populations in Fig. 4. The regression slope of linear equation followed the order of T3 (0.33) > T1 (0.20) > T2 (0.09).

3.2 Spatial distribution of S. moorcroftiana population

3.2.1 Elevation

Fig. 5 and Fig. 6 showed the changes of individual distribution ofS. moorcroftiana extracted in each topography along elevation. In three topographies, the elevation spans from 3550 m (T1) to 3695 m (T3). The population density decreased with increasing elevation (Fig. 5). The ρ value spanned from 1.7 to 0.1 and showed the decreasing trend along elevations, with the largest and smallest values in T1 and T3, respectively (Fig. 6). However, there were some differences for the different topographies. The decreasing trend along elevations was showed in T1 and T3, with the ρ value of 1.7-0.5 and 0.4-0.1, respectively. While the ρ value for T2 had increased minimally from 0.2 to 0.5 with increasing elevation. In general, the height of individual S. moorcroftiana shrubs was positively related to elevation from 3550 m to 3695 m (r = 0.167; p < 0.01) (Fig. 7).

3.2.2 Slope

The spatial distribution of S. moorcroftiana population for different topography along slope was showed in Fig. 8 and Fig. 9. The order of overall slope in different topographies was T3 (35°) > T2 (25°) > T1 (5°). The value of slope ranged between 0° and 80° in T1 and spanned from 0° to 84° in T2 and T3. Although the spatial distribution of S. moorcroftiana population in different topography along slope had differences, there was similar to the overall trend, which was decreasing firstly, increasing secondly and decreasing finally with increasing slope (Fig. 9). In T1, the ρ value was decreasing from 1.74 to 0.85 with the slope of 0° - 2.6°, and then increasing to 1.52 with the slope of 2.6° - 15.8°, and finally showed irregular fluctuation with the maximum value of 2.84 at 48° and minimum value of 0.01 at 42°. However, there was obvious regulation for the changes of ρ value along slope in T2 and T3. In T2, the decreasing trend was happened before the slope of 10.6° and after the slope of 20.3°, with the ρ value of 1.88 – 0.42 and 0.75 - 0.03, respectively. While the maximum ρ value was 0.27 at 50.6° and the minimum ρ value was 0.10 at 5.6° in T3. In general, the individual height of S. moorcroftiana population exhibited significant correlation with slope from 0° to 84° (r = 0.145; p < 0.01) (Fig. 7).

3.2.3 Aspect

Fig. 10 and Fig. 11 showed the spatial distribution of S. moorcroftiana population had large difference for the changes of aspect in different topographies. The minimum ρ value was showed on the north for all of topographies. In T1, the ρ value in different aspects follows the order of Southwest (1.23) > Southeast (1.21) > South (1.10) =West (1.10) > East (1.06) > North (0.62). In T2, the ρ value was Southwest (0.78) > Northeast (0.68) > East (0.63) > West (0.55) > South (0.53) > North (0.38). While the maximum ρ value was 0.26 on the Northeast and then followed as East (0.23), South (0.21), West (0.16), North (0.13) decreasingly in T3.