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.