Xinwen Xu’s research while affiliated with State Key Laboratory of Desert and Oasis Ecology, Chinese Academy of Sciences and other places

Tumbleweeds participate in a common seasonal biological process in temperate grasslands, creating hanging grass fences during the grass-withering season that result in distinct ecological phenomena. In this study, we addressed the urgent need to understand and restore the degraded desert steppe in Central Mongolia, particularly considering the observed vegetation edge effects around hanging grass fences. Using field surveys conducted in 2019 and 2021 in the severely degraded desert steppe of Central Mongolia, we assessed vegetation parameters and soil physical and chemical properties influenced by hanging grass fences and identified the key environmental factors affecting vegetation changes. The results indicate that the edge effects of hanging grass fences led to changes in species distributions, resulting in significant differences in species composition between the desert steppe's interior and edge areas. Vegetation parameters and soil physical and chemical properties exhibited nonlinear responses to the edge effects of hanging grass fences, with changes in vegetation coverage, aboveground biomass, and soil sand content peaking at 26.5, 16.5, and 6.5 m on the leeward side of hanging grass fences, respectively. In the absence of sand dune formation, the accumulation of soil organic carbon and available potassium were identified as crucial factors driving species composition and increasing vegetation coverage. Changes in species composition and plant density were primarily influenced by soil sand content, electrical conductivity, and sand accumulation thickness. These findings suggest that hanging grass fences have the potential to alter vegetation habitats, promote vegetation growth, and control soil erosion in the degraded desert steppe of Central Mongolia. Therefore, in the degraded desert steppe, the restoration potential of hanging grass fences during the enclosure process should be fully considered.

The Taitema Lake Basin serves as an ecological barrier in the south of the Tarim Basin, connecting with the Qiemo, Ruoqiang, and Milan oases, collectively preventing the expansion and merging of the desert, specifically inhibiting the convergence of the Taklamakan Desert and Lop Nur. In recent years, with changes in the natural environment and an increase in water usage, the downstream flow of the Tarim River has decreased, leading to the gradual drying up of Taitema Lake and exacerbating desertification, resulting in frequent sandstorms. Subsequently, under the influence of ecological water transfer projects, Taitema Lake has gradually recovered, and the ecological environment has improved. This study focuses on Taitema Lake and its nearby regions, constructing the Regional Landscape Ecological Risk Index (ERI) to assess landscape ecological risks before and after ecological engineering and determine ecological benefits. The results indicate that the EWC (Ecological Water Conveyance) project effectively supplements water in the intermediate and lower courses of the Tarim River and the terminal lakes, significantly bolstering ecological conditions in the lake basin and reducing risks. However, the current EWC project is relatively extensive, and the water reaching the Tarim River and Taitema Lake depends entirely on the surplus water from upstream production and daily life. Additionally, the distribution of downstream water depends entirely on natural topography, leading to uneven spatiotemporal distribution of water resources and significant evaporation losses. Rational hydraulic engineering measures should be taken to re-plan the distribution of rivers and lakes, achieving the maximum ecological benefits of the EWC project.

The spread of woody plant encroachment is a major concern as it adversely affects herbaceous plant community composition in a savanna ecosystem. Assessing the canopy effects of co-occurring encroaching and non-encroaching woody plant species on the understory herbaceous vegetation biomass and the soil nutrient status can improve our understandings of the link between biological invasions and herbaceous plant community ecology. We examined the canopy and adjacent inter-canopy effects of encroaching and non-encroaching Vachellia species which was previously known as Acacia on herbaceous vegetation biomass in Southern Ethiopia. A total of 12 encroaching (Vachellia drepanolobium) and 12 non-encroaching (Vachellia tortilis) tree species were selected both at an upland and a bottomland site. A 1 m × 1 m quadrat was used to investigate the canopy effects of individual tree species and inter-canopy habitats on herbaceous vegetation biomass. Soil samples were collected under the canopy of selected tree species and the adjacent inter-canopy habitat at a depth of 0–10 cm and 10–20 cm both at the upland and bottomland site. With fixed effect ANOVA, we evaluated the effects of landforms (upland or bottomland), tree species (Vachellia drepanolobium or Vachellia tortilis) and habitats (canopy or inter-canopy habitat) on total herbaceous biomass, perennial herbaceous species biomass and annual herbaceous species biomass. There was no significant (P > 0.05) difference between the canopy and inter-canopy habitat of V. drepanolobium and V. tortilis in terms of the total herbaceous biomass and annual herbaceous vegetation at the bottomland position. The canopy of V. drepanolobium had a negative effect on the biomass production of herbaceous perennial species both at the bottomland and upland site. On the contrary, the canopy of V. tortilis had a significantly positive (P < 0.05) effect on the biomass production of herbaceous perennial plants at the bottomland site. Generally, more soil organic matter accumulation was recorded under the canopy of V. tortilis than it was either under the canopy of V. drepanolobium or in the open savanna grasslands. Our findings indicated that encroaching tree species canopy and co-occurring non-encroaching tree species canopy had a predominantly different influence on herbaceous vegetation biomass. It seemed that encroaching tree species in savannas had a high acquisition and competition for resources. The findings can help improve our understanding on the herbaceous biomass predictions of different life forms in a community of encroached grasslands and non-encroached grasslands in southern Ethiopia.

Woody plant encroachments are major concerns across the grasslands biome, while the patterns of individual species existence at a landscape level can be limited locally and regionally. The paper assesses the species composition, community structure, and density of individual and combined encroacher woody species in terms of tree equivalent per hectare (TE ha⁻¹) within five different height classes at four elevation levels in Borana arid thorn bush savanna grasslands in Southern Ethiopia. At each elevation class, a grid of 20 × 20 m main plot was placed, and samples were collected randomly from three 100 m² sub-plot within the main plot. Using a single-factor analysis of variance, the effects of four elevation classes were considered on encroacher woody plant species composition, total, and individual density (TE ha⁻¹) within height classes. A total of 22 encroacher woody plant species composition were identified. The identified woody plants are seemingly a threat to the Borana rangelands of Southern Ethiopia with various patterns of distribution and density (TE ha⁻¹) among the different elevation levels. Of the identified species, Acacia reficiens had the highest density (1052.22 ± 265.34 TE ha⁻¹) at elevation level II. The most important encroaching species in each elevation level was varied considerably, while the combined woody plants density (TE ha⁻¹) within height classes across elevation levels showed minimal variations. This suggests that the management of a specific ecological site might require greater focus in terms of the functional traits of individual woody species composition, density coverage within height classes, and community structure. Hence, identifying the patterns, distribution, and density of encroaching woody species is crucial for the control of key encroacher woody species at a landscape level.

Haloxylon ammodendron is crucially important for stabilizing sand dunes in the desert area of the Junggar Basin and has thus been widely planted in the oasis–desert ecotone for windbreak and sand fixation purposes since the 1980s. The spatial distribution and structural characteristics of Haloxylon ammodendron plantations of three different ages—planted in 1983 (36a), 1997 (22a), and 2004 (15a)—on the southwestern edge of the Gurbantünggüt Desert were studied. The results showed that the spatial distribution patterns for the different stages of growth showed a trend of cluster that was random during the transformation from seedlings to juvenile and mature trees. Forest density for the 15a, 22a, and 36a plantations was, respectively, 1110, 1189, and 1933 plants ha−1; the base stem diameter for the main forest layer was 5.85, 8.77, and 6.17 cm, respectively, and the tree height was concentrated in the range of 1.5–3.0 m, 2.0–3.5 m, and 1.5–2.5 m. In the regeneration layers, the proportion of seedlings was the largest in all three stand ages, followed by juvenile trees, and mature trees only appeared in the 22a plantation. The proportion of deadwood in the 36a forest was the highest, and there were no mature trees in the regeneration layer. These results indicate that the three Haloxylon ammodendron plantation stages were in the period of rising at 15a, stable and degenerate with increasing age at 22a, and at 36a the regeneration ability was very weak and presented degradation due to species competition for soil moisture, because of too many seedlings and mature plants. In this case, measures such as thinning could be taken to prevent rapid degradation and to accelerate regeneration when the stand age exceeds 20 years. Considering the sand fixation effect, the pressure of competition for water resources, and forest capacity for renewal and sustainability, the most suitable forest density in the Haloxylon ammodendron plantation would be 8.5–9 m2 per plant.

Political instability (PI) occurs between governments and other political elites either at the local, regional, and/or national levels. Planning, implementing, and monitoring of sustainable rangeland management strategies have a significant impact on the political environment of an area. In this study, the term PI implies an unsafe and unstable exercise of political power, and is a major obstacle to the implementation of sustainable rangeland management. The main purpose of this research was to provide empirical and theoretical knowledge by testing hypotheses about the impact of PI on the implementation of sustainable practice of rangeland management. Using in-depth interviews, this study conducted both structured and unstructured group discussions with 300 representative households of local pastoralists and others who were considered the key stakeholders in the sustainable activities of rangeland management. Results indicated that the local communities are significantly susceptible to the economic, environmental, and socio-cultural effects of sustainable management of rangeland due to PI. Furthermore, the impact of PI on the economic, environmental, and socio-cultural aspects of rangelands indicators was evaluated. The findings also proved that the satisfaction of pastoralists with rangeland productivity and function was significantly affected, and prevented pastoralists from participating in rangeland management practice.

Abstract A study on the effect of bush control methods on encroaching woody species, namely Acacia drepanolobium, Acacia mellifera and Acacia reficiens was conducted for a 2 years’ time. A 3 ha of land was divided into two plots. Each replication with an area of 300 m × 50 m was again sub-divided into six plots (each 50 m × 50 m) to accommodate six treatments. Bush control treatments were assigned randomly to the plots and replicated two times across sites of similar topography. During the post-treatment period, responses of woody species to different treatments in terms of mortality and coppicing were monitored. Data was analysed using R software and Tukey’s studentized range tests for comparisons of means. The applied treatments significantly influenced (P

Desertification is one of the most serious environmental problems in the world, especially in the arid desert regions. Combating desertification, therefore, is an urgent task on a regional or even global scale. The Taklimakan Desert in China is the second largest mobile desert in the world and has been called the “Dead Sea” due to few organisms can exist in such a harsh environment. The Taklimakan Desert Highway, the longest desert highway (a total length of 446 km) across the mobile desert in the world, was built in the 1990s within the Taklimakan Desert. It has an important strategic significance regarding oil and gas resources exploration and plays a vital role in the socio-economic development of southern Xinjiang, China. However, wind-blow sand seriously damages the smoothness of the desert highway and, in this case, mechanical sand control system (including sand barrier fences and straw checkerboards) was used early in the life of the desert highway to protect the road. Unfortunately, more than 70% of the sand barrier fences and straw checkerboards have lost their functions, and the desert highway has often been buried and frequently blocked since 1999. To solve this problem, a long artificial shelterbelt with the length of 437 km was built along the desert highway since 2000. However, some potential problems still exist for the sustainable development of the desert highway, such as water shortage, strong sandstorms, extreme environmental characteristics and large maintenance costs. The study aims to provide an overview of the damages caused by wind-blown sand and the effects of sand control measures along the Taklimakan Desert Highway. Ultimately, we provide some suggestions for the biological sand control system to ensure the sustainable development of the Taklimakan Desert Highway, such as screening drought-resistant species to reduce the irrigation requirement and ensure the sound development of groundwater, screening halophytes to restore vegetation in the case of soil salinization, and planting cash crops, such as Cistanche, Wolfberry, Apocynum and other cash crops to decrease the high cost of maintenance on highways and shelterbelts.