Wind erodibility indices of aeolian sandy soils impacted by different vegetation restoration:a case study from the Shannan valley of the Yarlung Zangbo River

Controlling aeolian desertification is a key ecological target on the Tibetan Plateau,especially within the widespread river valleys.Vegetation recovery can change the near-soil surface characteristics,which thus may influence wind erodibility of soils.However,these potential effects are not sufficiently evaluated for aeolian sandy soils.This study selected the Shannan valley of the Yarlung Zangbo River on the southern Tibetan Plateau as a case to investigate the variations in wind erodibility of aeolian sandy soils impacted by different vegetation restoration,since many ecological measures have been implemented in recent decades in the river valley.Eight vegetated sandy lands with different restoration types and ages and two bare sandy lands(as controls)were chosen as test sites.Four vegetated sandy lands were covered by Artemisia wellbyi,Hedysarum scoparium,Sophora moorcroftiana,and Populus L.with the similar restoration age of 10 years.For Sophora moorcroftiana and Populus L.communities,two restoration ages of 6 and over 30 years were also selected respectively.Wind erodibility was reflected by wind erodible fraction(EF),mean weight diameter of dry aggregates(MWD),capillary water capacity(CWC),soil cohesion(CS),and soil penetration resistance(PR)from different aspects.A comprehensive wind erodibility index(CWEI)was further produced by a weighted summation method to combine those five indices together and comprehensively quantify the effects of vegetation restoration on wind erodibility of aeolian sandy soils.The results showed that revegetation was efficient to reduce wind erodibility of aeolian sandy soils.EF generally decreased,while MWD,CWC,CS,and PR increased after vegetation restoration on the aeolian sandy lands.The CWEI of vegetated sandy lands varied greatly from 0.850 to 0 under different restoration types and ages and decreased by 14.4%to 100%compared to the control.Under the four different restoration types,Populus L.had the relatively minimum CWEI,followed by Artemisia wellbyi,Sophora moorcroftiana and Hedysarum scoparium.With succession from 6 to over 30 years,CWEI gradually declined for both the Populus L.and Sophora moorcroftiana restored sandy lands.The decreases in wind erodibility(reflected by CWEI)on vegetated sandy lands were dominantly controlled by the improvement of soil texture and the increases of organic matter and calcium carbonate contents with vegetation restoration.The combined vegetation measure of Populus L.mixed with shrubs and grasses was suggested as the optimal restoration type for mitigating wind erodibility of aeolian sandy soils in the Shannan valley of the Yarlung Zangbo River.

Diverse Climatic and Anthropogenic Impacts on Desertification in the Middle Reaches of Yarlung Zangbo River Catchment on the Tibetan Plateau

The unique desertification processes occurring under the Alpine climate and ecosystem on the Tibetan Plateau could provide critical clues to the natural and anthropogenic impacts on desertification.This study used the Landsat data to investigate the spatial and temporal distribution of desertification from 1990 to 2020 in two areas(Shannan and Mainling),within the Yarlung Zangbo River Basin.The results show not only distinct spatial patterns but also various temporal changes of desertification.In Shannan,aeolian sand was distributed over wide areas from valley floor to mountain slope,while in Mainling,it is distributed sporadically at the footslope.The aeolian sandy land initially expanded before undergoing long-term shrinkage in Shannan.While in Mainling,it steadily expanded followed by a rapid decrease.These changes are attributed to both climate change and human activites.The increase in temperature causes desertification expansion in Shannan,while favorable climate conditions coupled with decreasing human activity promoted desertification reversal.However,both the expansion and shrinkage of desertification were sensitive to human activity in Mainling.This highlights the diverse responses of desertification to natural and anthropogenic impacts on different backgrounds of climatic and vegetation coverage.A threshold of climatic conditions may control the dominance factors in desertification,shifting from natural to anthropogenic elements.

Land surface roughness impacted by typical vegetation restoration projects on aeolian sandy lands in the Yarlung Zangbo River valley,southern Tibetan plateau

Aeolian sandy lands are widespread and desertification is recognized as one of the main environmental issues in the Yarlung Zangbo River valley,southern Tibetan plateau.The surface microtopographic var-iations induced by the near soil surface characteristics of plant communities are important compositions of land surface roughness,which likely influence wind erosion.This study was conducted to quantify the effects of typical vegetation restoration on land surface roughness on the aeolian sandy lands,and to identify the main influencing factors of land surface roughness in the Yarlung Zangbo River valley.Two bare sandy lands(as controls)and eight vegetated sandy lands with different restoration communities and ages were selected,and land surface roughness(LSR),as represented by surface microtopographic variations in this study,was measured by photogrammetric surveys.The results showed that LSR significantly increased by 7.9-16.8 times after vegetation restoration on the aeolian sandy lands,and varied among different restoration communities and ages.The mostly restored communities of Sophora moorcroftiana and Populus L.had greater LSR as compared to Artemisia wellbyi and Hedysarum scoparium.With succession from 6 to over 30 years,LSR gradually increased in the Sophora moorcroftiana restored sandy lands,but decreased in the Populus L restored sandy lands.The variations of LSR were mainly attributed to the differences in near soil surface characteristics of vegetation(plant stem diameter and coverage,and plant residue density)and biological soil crusts(coverage and thickness).Mixed plantation of Populus L and Sophora moorcroftiana was considered as the best restoration communities because of their effectiveness in increasing land surface roughness on the aeolian sandy lands in the Yarlung Zangbo River valley.The results would facilitate the understanding of the benefits of vegetation restoration in controlling wind erosion on the aeolian sandy lands.