•We simulated the human-induced alpine grassland NPP over the Qinghai–Tibet plateau.•We separated the influences caused by climate change and anthropogenic activities.•We found the different driving ...forces for the consistently enhanced actual NPP.•National grassland protection policy has achieved positive ecological effects.
Climate change and anthropogenic activities are two factors that have important effects on the carbon cycle of terrestrial ecosystems, but it is almost impossible to fully separate them at present. This study used process-based terrestrial ecosystem model to stimulate the potential climate-driven alpine grassland net primary production (NPP), and Carnegie–Ames–Stanford Approach based on remote sensing to stimulate actual alpine grassland NPP influenced by both of climate change and anthropogenic activities over the Qinghai–Tibet plateau (QTP) from 1982 to 2011. After the models were systematically calibrated, the simulations were validated with continuous 3-year paired field sample data, which were separately collected in fenced and open grasslands. We then simulated the human-induced NPP, calculated as the difference between potential and actual NPP, to determine the effect of anthropogenic activities on the alpine grassland ecosystem. The simulation results showed that the climate change and anthropogenic activities mainly drove the actual grassland NPP increasing in the first 20-year and the last 10-year respectively, the area percentage of actual grassland NPP change caused by climate change declined from 79.62% in the period of 1982–2001 to 56.59% over the last 10 years; but the percentage change resulting from human activities doubled from 20.16% to 42.98% in the same periods over the QTP. The effect of human activities on the alpine grassland ecosystem obviously intensified in the latter period compared with the former 20 years, so the negative effect caused by climate change to ecosystem could have been relatively mitigated or offset over the QTP in the last ten years.
•Grazing exclusion increased ecosystem carbon stocks in degraded grasslands in China.•Grazing exclusion is more efficient in humid than arid grasslands in terms of C sequestration.•Soil carbon ...sequestration rates decayed rapidly over time.•Grazing exclusion has little effect on plant diversity recovery.•The RGLG program over ten years should be ceased and substituted by other integrated practices.
Widespread land degradation has strengthened the urgent need to restore overgrazing grasslands. China has implemented the program ‘Returning Grazing Land to Grassland’ (RGLG) through grazing exclusion by fence since 2003. Despite a lot of field experiments, there is still controversy on the effects of grazing exclusion on rangeland restoration, highlighting the need for synthetic analysis. We conducted a meta-analysis of 447 entries from 78 papers to analyze the spatiotemporal effects of grazing exclusion on plant diversity, productivity and soil carbon sequestration in the major RGLG-implemented provinces of China. Our results showed that, compared with the grazed sites, grazing exclusion significantly increased carbon stored in aboveground biomass, litter mass, belowground biomass and soils by 84.7%, 111.6%, 25.5% and 14.4%, respectively. Plant coverage, soil available nitrogen, soil available phosphorus and soil microbial biomass carbon increased by 52.0%, 21.7% 22.8% and 26.3%, respectively. However, grazing exclusion had little effects on recovering plant diversity in China’s grasslands. Of the factors examined, climatic factors strongly modified the effects of grazing exclusion on ecosystem carbon stocks, for example, precipitation significantly amplified the positive effects. Grazing exclusion played a positive role in soil carbon sequestration in most grassland types except in temperate desert-steppe. But annual soil carbon sequestration rates decayed rapidly over time in both alpine meadow and temperate steppe. Short-term (≤5years) grazing exclusion remarkably increased species richness, but not significantly in the long run. The threshold from neutral to negative effects of grazing exclusion on species evenness occurs after approximately ten years. Our findings provide evidence that grazing exclusion is an effective way to restore vegetation and sequestrate carbon in degraded grasslands, but not beneficial to plant diversity maintenance. The benefits of grazing exclusion are more effective in humid area than arid area. We suggest that grazing exclusion should be ceased after about six to ten years. Additionally, grazing exclusion should integrate with other appropriate management practices instead of operating on a stand-alone basis.
Biomass allocation is an essential concept for understanding above- vs. below-ground functions and for predicting the dynamics of community structure and ecosystem service under ongoing climate ...change. There is rare available knowledge of grazing effects on biomass allocation in multiple zonal alpine grassland types along climatic gradients across the Northern Tibetan Plateau. We collected the peak above- and below-ground biomass (AGB and BGB) values at 106 pairs of well-matched grazed vs. fenced sites during summers of 2010-2013, of which 33 pairs were subject to meadow, 52 to steppe and 21 to desert-steppe. The aboveground net primary productivity (ANPP) was represented by the peak AGB while the belowground net primary productivity (BNPP) was estimated from ANPP, the ratio of living vs. dead BGB, and the root turnover rate. Two-ways analyses of variance (ANOVA) and paired samples comparisons with t-test were applied to examine the effects of pasture managements (PMS, i.e., grazed vs. fenced) and zonal grassland types on both ANPP and BNPP. Allometric and isometric allocation hypotheses were also tested between logarithmically transformed ANPP and BNPP using standardized major axis (SMA) analyses across grazed, fenced and overall sites. In our study, a high community-dependency was observed to support the allometric biomass allocation hypothesis, in association with decreased ANPP and a decreasing-to-increasing BNPP proportions with increasing aridity across the Northern Tibetan Plateau. Grazing vs. fencing seemed to have a trivial effect on ANPP compared to the overwhelming influence of different zonal grassland types. Vegetation links above- and below-ground ecological functions through integrated meta-population adaptive strategies to the increasing severity of habitat conditions. Therefore, more detailed studies on functional diversity are essentially to achieve conservation and sustainability goals under ongoing climatic warming and intensifying human influences.
•A red-edge spectral indices (RESI) was firstly applied to detect rubber plots.•The 20-m Sentinel-based map of the rubber was first generated in northern Laos.•A twelfth of rubber plantations were ...planted in the protected area of Luang Namtha.
Rubber (Hevea brasiliensis) tree cultivation is being continuously expanded northward by replacing evergreen forests and swidden-related regenerated vegetation across the uplands of mainland Southeast Asia (MSEA), e.g., Laos, a landlocked mountainous country. The non-native tree establishment in the northern tropical edge, or the non-traditional suitable planting area, provides stable supplies of natural latex, yet also leads to severe ecological degradation and environmental effects in water conservation, soil quality, rainforest fragmentation and biodiversity. Rubber plantations in the northern part of MSEA are normally characterized by periodic deciduous during the dry season, along with a lengthy defoliation-foliation duration, because of seasonal variations in temperature and precipitation. It thus lays a phenological and physiological base for dynamics monitoring with common multispectral (e.g., near-infrared and short-wave infrared bands) satellites, particularly Landsat. However, whether Sentinel-2 red-edge based algorithms are suitable for discriminating rubber plantations is not yet exclusively reported. Here, we developed a red-edge spectral indices (RESI) method through the normalization of three red-edge bands and applied it to identify and map rubber plantations in Luang Namtha Province of northern Laos, where a rubber boom begun in the mid-2000s. The RESI algorithm highlights the sensitivity of red-edge bands to the changes in moisture content and canopy density of rubber plantations. The area of mature rubber plantations was estimated to be 771.2 km2 in this province bordering southwest China in 2018, which was nearly twice as much as that of 2011, with the overall accuracy and kappa coefficient up to 92.50% and 0.91, respectively. Our phenology-based RESI approach not only indicates that Sentinel-2 imagery holds significant potential for monitoring rubber plantations, but also improves the remotely-sensed methods of rubber boom mapping via introducing the red-edge channel.
Driver fatigue is one of the leading factors contributing to road crashes. Environmental stress, such as unwanted seat vibration, is a key contributor to fatigue. This article presents the design and ...development of a magnetorheological elastomer isolator for a seat suspension system. By altering the magnetorheological elastomer isolator’s stiffness through a controllable magnetic field and selecting suitable control strategy, the system’s natural frequency can be changed to avoid resonance, which consequently reduce the vehicle’s vibration energy input to seat, and thus suppress the seat’s response. Experimental results show that the developed magnetorheological elastomer isolator is able to reduce vibration more when compared with the passive isolation system, indicating the significant potential of its application in vehicle seat vibration control.
Aim Carbon use efficiency net primary production (NPP)/gross primary production (GPP) ratio is a parameter related to the allocation of photosynthesized products by plants and is commonly used in ...many biogeochemical cycling models. But how this parameter changes with climates is still unknown. Faced by an aggravated global warming, there is a heightened necessity in unravelling the dependence of the NPP/GPP ratio on climates. The objective of this study was to examine how ongoing climate change is regulating global patterns of change in the NPP/GPP ratio. The study finding would elucidate whether the global vegetation ecosystem is becoming more or less efficient in terms of carbon storage under climatic fluctuation. Location The global planetary ecosystem. Methods The annual NPP/GPP ratio of the global terrestrial ecosystem was calculated over a 10-year period based on Moderate Resolution Imaging Spectro-radiometer data and an ecosystem productivity model. The temporal dynamics of the global NPP/GPP ratio and their dependence on climate were investigated. Results The global NPP/GPP ratio exhibited a decreasing trend from 2000 to 2009 due to decreasing NPP and stable GPP over this period. The temporal dynamics of the NPP/GPP ratio were strongly controlled by temperature and precipitation. Increased temperature lowered the NPP/GPP ratio, and increased precipitation led to a higher NPP/GPP ratio. Conclusions The NPP/GPP ratio exhibits a clear temporal pattern associated with climatic fluctuations at a global scale. The associations of the NPP/GPP ratio with climatic variability challenge the conventional assumption that the NPP/GPP ratio should be consistent independent of environmental conditions. More importantly, the findings of this study have fundamental significance for our understanding of ongoing global climatic change. In regions and time periods experiencing drought or increased temperatures, plant ecosystems would suffer a higher ecosystem respiration cost and their net productivity would shrink.
Density functional theory (DFT) calculations were performed for a series of imidazole derivatives. B3LYP and B3P86 functionals with 6-31G** basis set were used. Heats of formation (HOFs) were ...predicted through designed isodesmic reactions. Calculated results show that the HOFs relate to the number and the position of nitro groups. The HOFs increase with the augment of the number of the NO
2 group for the direct imidazole derivatives and decrease with the augment of the number of the NO
2 group for 1-picrylimidazole derivatives. Thermal stabilities were evaluated via bond dissociation energies (BDEs). The result shows that the increase of nitro group number on imidazole ring reduces the stability of the molecule. Further, the correlation was developed between impact sensitivity
h
50 and the ratio (BDE/
E) of the weakest bond BDE to the total energy
E. The detonation performance data were also calculated.
The natural shift in land cover from non-vegetated to vegetated land is termed as vegetation expansion, which has substantial impacts on regional climate conditions and land surface energy balance. ...Barrens dominate the northwestern Tibetan Plateau, where vegetation is predicted to expand northwestward with the ongoing climate warming. However, rare studies have confirmed such a forecast with large-scale vegetation monitoring. In this study, we used a landcover dataset, classified according to the International Geosphere–Biosphere Program criteria, to examine previous model-based predictions and the role of climate on the expansion rate across the plateau. Our results showed that shrublands, open forests, grasslands, and water bodies expanded while evergreen and deciduous broadleaf forests, croplands and barrens shrank during the period 2001–2018. Vegetation expanded by 33,566 km2 accounting for about 1.3% of the total area of this plateau and the land cover shifting from barrens to grasslands was the primary way of vegetation expansion. Spatially, the vegetation expanded northwestward to lands with colder, drier, and more radiation in the climate. Increasing precipitation positively correlated with the vegetation expansion rate for the arid and semi-arid northwest Tibetan Plateau and warming contributed to the vegetation expanding in the semi-humid southeast Tibetan Plateau. Our results verified the predictions of models and highlighted the “greening” on barrens in recent years.
Increasing atmospheric nitrogen (N) deposition has the potential to alter plant diversity and thus the function and stability of terrestrial ecosystems. N-limited alpine ecosystems are expected to be ...particularly susceptible to increasing N deposition. However, little is known about the critical loads and saturation thresholds of ecosystem responses to increasing N deposition on the Tibetan Plateau, despite its importance to ecosystem management. To evaluate the N critical loads and N saturation thresholds in an alpine ecosystem, in 2010, we treated an alpine meadow with five levels of N addition (0, 10, 20, 40, and 80 kg N ha⁻¹ year⁻¹) and characterized plant and soil responses. The results showed that plant species richness and diversity index did not statistically vary with N addition treatments, but they both changed with years. N addition affected plant cover and aboveground productivity, especially for grasses, and soil chemical features. The N critical loads and saturation thresholds, in terms of plant cover and biomass change at the community level, were 8.8–12.7 and 50 kg N ha⁻¹ year⁻¹ (including the ambient N deposition rate), respectively. However, pronounced changes in soil inorganic N and net N mineralization occurred under the 20 and 40 kg N ha⁻¹ year⁻¹ treatments. Our results indicate that plant community cover and biomass are more sensitive than soil to increasing N inputs. The plant community composition in alpine ecosystems on the Qinghai-Tibetan Plateau may change under increasing N deposition in the future.
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