5 Conclusion

The TLS, a new and powerful tool, was used to accurately extract the parameters of vegetation and micro-topography during the natural restoration of S. moorcroftiana population on the degraded land in this study. The changes of structure of S. moorcroftianapopulation and effect of micro-topography on spatial distribution ofS. moorcroftiana population after natural restoration on an extremely degraded land were evaluated by the field investigation and TLS scans in the middle reaches of Yarlung Zangbo River in 2017. Since 2008, the effectiveness of natural restoration for S. moorcroftiana population had gradually improved in the Yarlung Zangbo River valley, Shannan city and the vegetation coverage had reached 30% - 58% in 2017. The dominant age structure ofS. moorcroftiana population were adults. The heights of individual shrubs ranged from 0.43 m to 0.74 m in different topographies, and the CPA ranged from 0.52 m2 to 4.13 m2. The west slope of approximately 25° with altitudes of 3593-3643 m (T2) has highest individual growth. The positive correlation between height and CPA reached the 99% confidence level (p < 0.01).
The measured elevation and slope spanned from 3550 m to 3695 m and from 0° to 84°, respectively. The elevation and slope exhibited significant positive correlations with plant height (r = 0.167 and 0.145, respectively; p< 0.01). However, the distribution of S. moorcroftianapopulation decreased along increasing elevation, while the overall trend of distribution of S. moorcroftiana population was decreasing firstly, increasing secondly and decreasing finally with increasing slope. There was little distribution of individuals on the west and north. Therefore, our results showed that the habitat conditions on the southwest slope of approximately 20°-25° with altitudes of 3593-3643 m most favor to the distribution and growth of S. moorcroftianapopulation in this region. In order to be able to advise managers on the effectiveness of natural restoration in producing ecological benefits of high value for community distribution and growth, along with optimized strategies of ecological restoration in the restored process, it is necessary to monitor and evaluate the structural development of population and spatial distribution of individuals after natural restoration.