Assessing revegetation effectiveness on an extremely degraded grassland, southern Qinghai-Tibetan Plateau, using terrestrial LiDAR and field data

The Qinghai-Tibetan Plateau (QTP) is one of the most difficult eco-regions for revegetation on degraded grassland because of its harsh environment. Micro-topography could affect habitat conditions important to ecological restoration on sandy land; however, the interaction between revegetation and micro-topography has been rarely reported on sand dunes of the QTP. Here, we quantified vegetation (including coverage, leaf area index (LAI), height, and crown diameter) and micro-topographic parameters (including elevation, slope, and aspect) to assess the effects of topography on revegetation using field observation data during 2008-2017 and terrestrial laser scanning (TLS) in 2017. The results showed that: 1) the tested plant species for revegetation has changed significantly from 2008 to 2017, and the current dominant plant species were mainly introduced from north China, including Hedysarum scoparium, H. fruticosum, and Artemisia sphaerocephala. 2) The effectiveness of revegetation has been improved remarkably over the past ten years. The vegetation coverage varies from 68.4% to 80.5% at four big quadrats of 20 m x 20 m, while the LAI value varies from 2.30 to 3.27, the shrub height ranges from 1.12 m to 7.57 m, and the crown diameter ranges from 0.24 m to 6.96 m. 3) A total of 153 shrubs were extracted in these four quadrats using TLS; and 56.9%, 21.6% and 10.5% of them are distributed on the southeastern, southern, and eastern aspects, respectively. The height and crown diameter of individual shrubs are significantly correlated with the local slope (p < 0.05) of which could affect the distribution of artificial seeding. These results suggest that aspect and slope are two key limiting factors for revegetation, and the habitat conditions on the southeastern and eastern aspects favor revegetation on valley-slope sand dunes. These findings provide a useful guidance in developing an integrated ecological restoration plan for sand dunes and selecting the best practice management of ecosystem services on degraded grassland on the QTP.