Agro-pastoral Ecotone Research Articles

Patterns and driving factors of soil ecological stoichiometry in typical ecologically fragile areas of China

Researchers are paying increasing attention to soil stoichiometry (carbon:nitrogen:phosphorus (C:N:P) ratios) in efforts to explore biogeochemical cycles, but little is known about the spatial pattern, implications, and driving factors of this stoichiometry in large, ecologically fragile areas. To explore these factors, we established three transects that covered a total length of about 4300 km in ecologically fragile areas of China, and sampled at intervals of about 25 km. These transects covered the karst area and the agro-pastoral ecotone of southwestern China, the Qinghai-Tibet Plateau, the Loess Plateau, and the forest-grassland ecotone. We collected 312 soil samples to a depth of 30 cm from 156 plots. The soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the ecologically fragile areas showed strong coupling relationships. Soil C:N:P was 51:4:1 to a depth of 30 cm, which is lower than the average global C:N:P (111:8:1). SOC and TN concentrations at 0 to 20 cm were significantly higher than that at 20 to 30 cm, but TP did not differ significantly among depths. SOC, TN, and TP concentrations were highest in the agro-pastoral ecotone, and were lowest in the Loess Plateau. C:N, C:P, and N:P were highest in the karst area. C:N were lowest in the Qinghai-Tibet Plateau, and C:P and N:P were lowest in the Loess Plateau. The spatial pattern of C, N, and P stoichiometry along environmental gradients was variable. The contributions to explaining the soil stoichiometry were highest for climate (21.7%), vegetation (8.9%), soil properties (6.4%), and topography (0.6%) to a depth of 20 cm, versus vegetation (35.9%), climate (5.3%), soil properties (3.3%), and topography (2.1%) at 20 to 30 cm. The results provide new insights into the biogeochemical cycles of C, N, and P and guidance for their impacts on ecological restoration in ecologically fragile areas.

Effects of long-term application of organic manure and chemical fertilizer on soil properties and microbial communities in the agro-pastoral ecotone of North China

Long-term irrational fertilizer inputs affect soil nutrients conditions in the agro-pastoral ecotone of North China. However, the mechanisms by which biotic and abiotic factors are affected by different fertilizer types remain unclear. A 16-year, long-term fertilization experiment was conducted to explore how soil physicochemical properties and microbial communities respond to different fertilizer types at an experimental site in North China. The key environmental factors that drove changes in soil microbial communities were also determined. In September 2019, soils were collected from plots of four fertilizer treatments: 1) non-fertilization control (CK), 2) chemical fertilization only (CF), 3) organic manure fertilization only (M), and 4) chemical fertilization plus organic manure (CFM). Compared with CK, soil organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium contents were higher in M and CFM, whereas soil pH was significantly lower in CF. Abundances of dominant soil bacterial phyla Proteobacteria, Bacteroidetes, and Gemmatimonadetes were higher in M and CFM than CK. Abundances of dominant soil fungal phyla Ascomycota was lower in CFM than in other treatments. The pathogenic fungi Fusarium, Paramyrothecium, Cladosporium, and Alternaria had the highest abundances in CK and CF, whereas abundances of the beneficial fungi Mortierella were significantly higher in M and CFM than in CF and CK. According to partial least squares path modeling, differences in fertilizer types had direct positive effects on fungal communities but little effect on bacterial communities. Overall, CFM maintained higher soil fertility and a healthy ecosystem because it increased beneficial microorganisms and inhibited pathogenic microorganisms, whereas CF increased the risk of crop infection with soil-borne diseases. The study provided a better understanding of how long-term fertilization affects microbial community composition and their associated ecosystem functions.

Exploring subjective well-being and ecosystem services perception in the agro-pastoral ecotone of northern China.

Understanding stakeholders' perceptions about human well-being and ecosystem services is essential for designing efficient public policies and sustainable environmental management that help to improve people's quality of life. Despite the fragile ecosystem and poverty concentration in the agro-pastoral ecotone, research in this field remains scarce. We selected a typical agro-pastoral ecotone, Duolun County, Inner Mongolia, China, to explore how socioeconomic and demographic factors affect subjective well-being and perceptions of ecosystem services through structural equation modelling (SEM) and canonical correspondence analysis (CCA). Our results showed that health had the highest correlation with subjective well-being among the five dimensions, but respondents were least satisfied with it. Formal education had the greatest effect on subjective well-being, followed by age, income, and livelihood. Gender had no effect on subjective well-being. Older respondents with lower formal education who had a lower level of subjective well-being considered supporting and provisioning services more important for well-being. In contrast, younger respondents with higher education levels (mostly jobs not associated with working the land) mainly valued cultural services. Finally, we discussed the factors that influence subjective well-being and perceptions of ecosystem services and their implications for local management decision-making.

Dynamic of land use, landscape, and their impact on ecological quality in the northern sand-prevention belt of China.

Changes in land use and landscapes have a direct impact on the regional eco-environment. It is of great importance to understand the change pattern of land use, landscapes, and their mechanism on the ecological quality, especially ecologically fragile areas. The northern sand-prevention belt (NSPB) is an important ecologically fragile area in China, which has a large influence on the ecological security of the entire country. Based on the land use data of the NSPB in 2000, 2010, and 2018, we studied the spatio-temporal characteristics of land-use change and change in landscape patterns. The ecological quality represented by the remote sensing-based desertification index (RSDI) was calculated using satellite images. The effects of land use and landscape patterns on RSDI were analyzed by geographic detector and geographically weighted regression. Important results include the following: (1) Land-use change in the study area was high during 2000-2010 but slower in 2010-2018. Grassland was the largest land-use type in the NSPB, and varied greatly in terms of total change and spatial location. The major change was the conversion between dense and moderate grass, with 64,860km2 of dense grass turning into moderate grass, and 48,505km2 changing the other way. (2) Among the four landscape metrics, patch density, area-weighted mean fractal dimension, and edge density increased, whereas the aggregation index decreased, which indicated that the landscape was developing towards heterogeneity, fragmentation, complexity, and aggregation. Spatially, the landscape metrics presented a strip distribution in the east of the NSPB. (3) The effects of various land-use types on ecological quality, from high to low, were unused land, woodland, dense grass, cropland, moderate grass, built-up land, sparse grass, and waterbody. The areas where the ecological quality was greatly affected by the landscape patterns were concentrated in the agro-pastoral ecotone and the forest-steppe ecotone. The results of this study reveal the trends of land use and landscape patterns in the NSPB over 18 years and can help to understand their mechanism on ecological quality, which is of significance for the management of this area.

Increasing land-use durations enhance soil microbial deterministic processes and network complexity and stability in an ecotone

Studies of community assembly and species interactions are updating our view of the mechanisms underpinning microbial diversity in single-type ecosystems, yet they are rarely conducted in ecotones, such as the agro-pastoral ecotone of northern China (APEN) undergoing frequent land-use conversions. In this study, soil microbial assembly processes and co-occurrence patterns were examined in different land-use types and durations across the APEN. The interpretation of remote sensing images revealed that current land-use types lasted 1 to 9 years for all samples. None of measured soil properties changed significantly between cropland and grassland, while silt and sand differed between the long (5 to 9 years) and short (1 to 4 years) duration. Soil microbial communities were assembled under consistent processes in both land-use types, but determinism clearly exhibited greater influences in the long duration than in the short one. The β-nearest taxon index (βNTI) decreased significantly with the durations in all samples and was also affected by total nitrogen (TN), soil organic matter (SOM), total phosphorus (TP), and clay. For the co-occurrence networks, nodes, edges, modularity, and the proportion of negative edges were similar between cropland and grassland, but obviously higher in the long duration than in the short one. Simultaneously, these metrics of the sub-networks had strong positive correlations with the durations, and weaker but significant correlations with TN, SOM, silt, and sand. Altogether, this study demonstrated that frequent land-use conversions might alleviate the impact of current land-use types, but highlight the importance of land-use durations on soil microbial community assembly and co-occurrence patterns in the APEN, and the deterministic processes and network complexity and stability increased with the durations, which advance the understanding of the mechanisms maintaining soil microbial diversity in ecotones.

Impacts of regional land-use patterns on ecosystem services in the typical agro-pastoral ecotone of northern China

ABSTRACT A comprehensive understanding of the spatial-temporal evolution and driving forces on ecosystem services (ES) is essential for the agro-pastoral ecotone’s ecological security in northern China. However, the land-use pattern (LULC) agglomeration with spatial differentiation in the pastoral and agricultural areas has been rarely concerned. Taking distinct LULC (1980–2018) in Chifeng as an example, we compared four crucial categories of ESs with InVEST. Using SEM, we further contrasted the effects of several variables on regional ES variations in pastoral-dominated (North) and agriculture-dominated (South) regions, respectively. Results revealed the conversion between forest and grassland oriented the LULC transformation in the North. In contrast, human-activitiy-oriented land tended to occupy environmentally sensitive places in the South. Similar ES variations were supplied with the North outperforming the South when soil conservation was omitted. As for the impacts of regional ES variations, the natural and LULC policies both showed positive effects, whereas the anthropogenic factors showed positive in the North, which was negative in the South. Therefore, the ecologically-maintained-dominant and ecologically-restored-dominant strategies should be separately adopted in the North and South. Our study provided appropriate regional ecological management suggestions for balancing the LULC-driven conflicts between ecological protection and regional development.

Influence of Different Proportion Intercropping on Oat and Common Vetch Yields and Nutritional Composition at Different Growth Stages

Crop yield mainly depends on environment and cultivation practices that vary according to a growing environment. However, an oat (Avena sativa L.)-common vetch (Vicia sativa L.) intercrop system has not been fully developed in the agro-pastoral ecotone of Inner Mongolia, China. This study evaluated the effects of seven treatments, including five oat-common vetch intercropping patterns, sole oat, and sole vetch on yield and quality performance at different growth periods [75 days after sowing (DAS), 90 DAS, 105 DAS], on the basis of field experiments conducted in the agro-pastoral ecotone of Inner Mongolia in 2015 and 2016. The OV3:1 (oat intercropped with common vetch at seeding ratios 3:1) treatment at 105 DAS in 2016 was superior to other treatments, as it achieved the highest shoot dry matter, increasing by 24.1% and 37.1% compared to sole oat and common vetch. The crude fat (CF) contents, CF yield, and crude protein (CP) yield increased under OV3:1, and acid detergent fiber (ADF) decreased under OV3:1, compared to monoculture. The results indicate that intercropping is an efficient cropping system for the agro-pastoral ecotone of Inner Mongolia. The appropriate proportion of oat and common vetch intercropping at 3:1 and harvesting time not only increases crop yield but also improves the crop quality.

Regional Potential Wind Erosion Simulation Using Different Models in the Agro-Pastoral Ecotone of Northern China.

Wind erosion is crucial for assessing regional ecosystem services and sustainable development. The Agro-Pastoral Ecotone of northern China (APEC) is a typical region undergoing wind erosion and soil degradation. In this study, the National Wind Erosion Survey Model of China, the Integrated Wind Erosion Modeling System, and the regional versions of the Revised Wind Erosion Equation and Wind Erosion Prediction System were used to evaluate the regional potential wind erosion of the APEC during 2000 and 2012. The results showed that the potential wind erosion predicted by National Wind Erosion Survey Model of China (NWESMC), Revised Wind Erosion Equation (RWEQ), Wind Erosion Prediction System (WEPS), and Integrated Wind Erosion Modeling System (IWEMS) were significantly related to the observed wind erosion collected from published literature, but the observed data were generally smaller than the predicted values. The average potential wind erosions were 12.58, 25.87, 52.63, and 58.72 t hm−2 a−1 for NWESMC, RWEQ, WEPS, and IWEMS, respectively, while the spatial pattern and temporal trend of annual potential wind erosion were similar for different wind erosion models. Wind speed, soil moisture, and vegetation coverage were the dominant factors affecting regional wind erosion estimation. These results highlight that it is necessary to comprehensively calibrate and validate the selected wind erosion models. A long-term standard wind erosion monitoring network is urgently required. This study can serve as a useful reference for improving wind erosion models.

Conversion of natural grassland to cropland alters microbial community assembly across northern China.

To feed the growing human population, natural grasslands are being converted to agricultural use at a massive scale. This conversion may have negative consequences for soil biodiversity, but its impact on the community assembly of differentially microbial groups remains largely unknown. Here, we investigated the diversity and community compositions of bacteria, archaea, fungi and protists, using a paired sampling of grassland and cropland soils across the agro-pastoral ecotone of northern China. Land-use conversion decreased α diversity of bacteria, fungi and protists, and altered the structures of the entire soil microbial community (archaea, bacteria, fungi and protists). The community assembly of archaea and bacteria was dominated by stochastic processes, and that of protists dominated by deterministic processes in both land-use types. By contrast, the fungal community was governed more strongly by stochastic processes in grassland soil, than by deterministic processes in cropland soil. Our findings support the 'size-plasticity' hypothesis that smaller body-sized microorganisms (archaea and bacteria) are more structured by stochastic processes, and larger one (protist) is more influenced by deterministic processes. Our study demonstrates that distinct ecological processes govern microbial community assembly, and land-use change regulates the balance between determinism and stochasticity.

Responses of Land-Use Changes to Drought and its Disparate Impact on Livelihoods of Farmers and Herders in the Agro-Pastoral Ecotone of Northwestern China

The agro-pastoral ecotone is an ecologically fragile region where drought is the main factor influencing land use and livelihoods. In this paper, we took two farmer villages and two herder villages in Ar Horqin Banner, located in the agro-pastoral ecotone of northwestern China, as the research areas, and where we conducted participatory rural appraisal and questionnaire survey to analyze the responses of land-use changes to drought and its disparate impact on the livelihoods of farmers and herders. Results show that: 1) Under drought, farmers tended to abandon rain-fed land, and herders tended to abandon grassland. 2) The livelihood activities of farmers were more stable than those of herders under drought. Farmers abandoned rain-fed farming, and herders just retained cattle rearing. The per capita net income of each farmer in Pingandi and Fenghuangling in the drought year of 2016 was only 9.27% and 12.52% lower than those in 2012, respectively, which was 132.88% and 128.25% lower than those in 2012 of each herder in Wuriduhubu and Haolibao. 3) Diversified livelihoods, especially non-agricultural ones, are the key to ensuring the sustainable livelihoods of farmers and herders. It is an effective way for farmers to encourage more labor force to emigrate to non-agricultural sectors. Regarding herders, it is urgent to develop artificial pastures and animal products processing industry with the support of government.

Tillage Promotes the Migration and Coexistence of Bacteria Communities from an Agro-Pastoral Ecotone of Tibet.

In the Tibetan agro-pastoral ecotone, which has an altitude of 4000 m above sea level, small-scale cropland tillage has been exploited on the grassland surrounding the houses of farmers and herdsmen. However, knowledge of the effects of land change from grassland to cropland on soil nutrients and microbial communities is poor. Here, we investigated the structure and assembly mechanism of bacterial communities in cropland (tillage) and grassland (non-tillage) from an agro-pastoral ecotone of Tibet. Results indicated that soil nutrients and composition of bacterial communities changed dramatically in the process of land-use change from grassland to cropland. The pH value and the content of total nitrogen, organic material, total potassium, and total phosphorus in cropland soil were well above those in grassland soil, whereas the soil bulk density and ammonia nitrogen content in grassland soil were higher than those in cropland soil. Proteobacteria (30.5%) and Acidobacteria (21.7%) were the key components in cropland soil, whereas Proteobacteria (31.5%) and Actinobacteria (27.7%) were the main components in grassland soils. Tillage promotes uniformity of bacterial communities in cropland soils. In particular, the higher migration rate may increase the coexistence patterns of the bacterial community in cropland soils. These results also suggest that the tillage promotes the migration and coexistence of bacterial communities in the grassland soil of an agro-pastoral ecotone. In addition, the stochastic process was the dominant assembly pattern of the bacterial community in cropland, whereas, in grassland soil, the community assembly was more deterministic. These findings provide new insights into the changes in soil nutrients and microbial communities during the conversion of grassland to cropland in the agro-pastoral ecotone.

Effect of Center-Pivot Irrigation Intensity on Groundwater Level Dynamics in the Agro-Pastoral Ecotone of Northern China

Groundwater-based irrigation is an effective buffer against water disconnects during droughts in areas of intensive agriculture. However, it is difficult to implement effective measures to sustainably utilize aquifers due to the unclear understanding of irrigation intensity in the agro-pastoral ecotone. To explore the influence of regional irrigation intensity on groundwater level (GL), we investigated the dynamics of Kernel density for irrigation well from 2000 and the changed GL (ΔGL in three groups) in a typical center-pivot irrigation (CPI) area (about 1,000 km2). The results showed that the implementation of CPI systems caused a rapid land-use change from natural grassland (NG) to cultivated pasture (CP). The observed ΔGL in deeper group (0.63 m yr−1, GL > 20 m) was significantly (p < 0.05) higher than that in shallower group (0.38 m yr−1, GL < 10 m) and medium group (0.43 m yr−1, 10 m < GL < 20 m). The predicted ΔGL and GL were significantly and positively correlated with the CPI well density (R2 = 0.447 and 0.429, p < 0.001), respectively, and showed a fitted plane function based on the variables (R2 = 0.655, p < 0.001). It indicted that the intensive cropping in the agro-pastoral ecotone profoundly changed regional irrigation intensity, resulting in a rapid response of the GL. To reduce the risk of increased irrigation costs and ensure sustainable availability of groundwater, it’s necessary to control the density of CPI systems in hotspot areas, and implement water-saving measures to balance water usage and recharge rates for sustainable groundwater management.

Mapping of Soil Organic Carbon Stocks Based on Aerial Photography in a Fragmented Desertification Landscape

Northern China’s agropastoral ecotone has been a key area of desertification control for decades, and digital maps of its soil organic carbon (SOC) stocks are needed to reveal the gaps between the actual SOC levels and baseline to support land degradation neutrality (LDN) under the Sustainable Development Goals. However, reliable soil information is scarce, and accurate prediction is hindered by the fragmented landscape, which is a dominant characteristic of desertified land. To improve the patchiness identification and accuracy of SOC prediction, we conducted field surveys and collected low-altitude aerial images along the desertification degrees (severe and extremely severe, moderate, slight) in the Horqin Sandy Land. Linear regressions were performed on the relationships between the normalized difference vegetation index and the fractional vegetation cover (FVC) extracted from aerial images, and regression kriging was applied to predict SOC stocks based on the soil-forming factors (vegetation, climate, and topography). Our prediction and cross-validation showed that the fragmented structure and prediction accuracy of SOC stocks were both greatly improved for desertified land. The FVC (R2c = 0.94) and evapotranspiration (R2c = 0.86) had significant positive effects on SOC stocks, respectively, with indirect and direct causal relationships. Our results could provide soil information with better patchiness and accuracy to help policymakers determine the future LDN status in this fragmented desertification landscape. As drone technology becomes more available, it will fully support digital mapping of soil properties.

Spatial Distribution of Optimal Plant Cover and Its Influencing Factors for Populus simonii Carr. on the Bashang Plateau, China

The Bashang Plateau is the core zone of the agro-pastoral ecotone in northern China and represents an ecological barrier for preventing the invasion of wind-blown sand in the Beijing–Tianjin–Hebei region. Increasing plant cover to control soil erosion is an effective measure to address land degradation; however, plant cover is different from climatic conditions. In this study, we determined the optimal spatial distribution of Populus simonii Carr., which is a widely planted species used for revegetation on the Bashang Plateau. A modified Biome-BGC model was used to simulate the dynamics of the net primary productivity (NPP), actual evapotranspiration (AET), and leaf-area index (LAI). The model was validated using field-observed tree-ring and MODIS AET and NPP data. The dynamics of AET, NPP and LAI for P. simonii at 122 representative sites in the study area for the period 1980–2019 were simulated by the validated model. The results showed that the spatial distributions of mean AET, NPP, and LAI generally decreased from southeast to northwest. The ranges of optimal plant cover in terms of maximum LAI for P. simonii were 3.3 in the Fengning–Weichang area, 1.9 in the Shangyi–Zhangbei–Guyuan area and 1.3 in the Kangbao area. Mean annual precipitation (MAP), elevation, soil texture and mean annual temperature were the main factors influencing the distribution of AET, NPP and LAI. As the MAP decreased, the correlations between AET, NPP, LAI and precipitation gradually decreased. In different subregions, the factors influencing optimal-plant-cover distribution varied significantly. These quantitative findings provide the optimal plant cover for the dominant tree in different subregions and provide useful information for land degradation management on the Bashang Plateau.

Measuring Compound Soil Erosion by Wind and Water in the Eastern Agro–Pastoral Ecotone of Northern China

Land degradation induced by soil erosion is widespread in semiarid regions globally and is common in the agro–pastoral ecotone of northern China. Most researchers identify soil erosion by wind and water as independent processes, and there is a lack of research regarding the relative contributions of wind and water erosion and the interactions between them in what is referred to here as compound soil erosion (CSE). CSE may occur in situations where wind more effectively erodes a surface already subject to water erosion, where rainfall impacts a surface previously exposed by wind erosion, or where material already deposited by wind is subject to water erosion. In this paper, we use the Chinese Soil Loss Equation (CSLE) and the Revised Wind Erosion Equation (RWEQ) to calculate the rate of soil erosion and map the distribution of three types of soil erosion classified as (i) wind (wind-erod), (ii) water (water-erod), and (iii) CSE (CSE-erod) for the study area that spans more than 400,000 km2 of sand- and loess-covered northern China. According to minimum threshold values for mild erosion, we identify water-erod, wind-erod, and CSE-erod land as occurring across 41.41%, 13.39%, and 27.69% of the total area, while mean soil erosion rates for water-erod, wind-erod, and CSE-erod land were calculated as 6877.65 t km−2 yr−1, 1481.47 t km−2 yr−1, and 5989.49 t km−2 yr−1, respectively. Land subject to CSE-erod is predominantly distributed around the margins of those areas that experience wind erosion and water erosion independently. The CSLE and RWEQ do not facilitate a direct assessment of the interactions between wind and water erosion, so we use these equations here only to derive estimates of the relative contributions of wind erosion and water erosion to total soil erosion and the actual mechanisms controlling the interactions between wind and water erosion require further field investigation. It is concluded that CSE is an important but underappreciated process in semiarid regions and needs to be accounted for in land degradation assessments as it has substantial impacts on agricultural productivity and sustainable development in regions with sandy and/or loess-covered surfaces.

Study on the Structural Properties of an Ecospatial Network in Inner Mongolia and Its Relationship with NPP

In the context of strengthening the construction of ecological civilization and accelerating the “carbon peak” in China, the regional ecological pattern and its connection with carbon sink capacity have become an urgent topic. Given that Inner Mongolia is a large carbon emission province and the conflict between economic development and ecological protection is particularly prominent, we took Inner Mongolia as an example to extract its ecospatial network, then calculated the integrity index, topological indices, and recovery robustness of the network and evaluated integrity and other properties of the ecospatial network structure by combining them with the ecological background. In addition, we analyzed the relationship between the topological indices and net primary productivity (NPP). The results showed that the network was scale-free and heterogeneous, with low integrity, connectivity and stability, which were the focus of future optimization. The nodes with important functions were mainly distributed in the farm-forest ecotone, grasslands, and the agro-pastoral ecotone; under the simulation attack, the node recovery robustness was stronger than the corridor recovery robustness, and NPP was negatively and significantly correlated with the woodland nodes and grassland nodes. In terms of ecological restoration, the unused land in the west is a key area, and it is necessary to add new ecological nodes and corridors. In terms of enhancing carbon sequestration capacity, under the premise of ensuring network connectivity, the appropriate and rational merging of ecological nodes and corridors within woodlands and grasslands is a particularly effective means. This study provides a reference for evaluating and optimizing the ecological pattern of areas with prominent ecological problems and improving the carbon sink of ecosystems in terms of their ecospatial network structure.

Village-level landscape succession and its driving mechanism in the agro-pastoral ecotone of Ningxia, China

The relationship between human activities and landscape patterns and its regulation are one of the core fields in landscape ecology. The ecological conditions and local cultures of agro-pastoral ecotone are gradually wea-kening due to environmental fluctuations, land-use characteristics (suitable for both farming and grazing), and unstable policy. Therefore, protecting and restoring this semi-natural landscape and the resulting biological, ecolo-gical and cultural functions are becoming increasingly urgent. Here, by combing remote sensing data with interview survey and geographic investigation, we characterized the landscape changes (1964 to 2019) of Wanjigou Village in Yanchi County of Ningxia Hui Autonomous Region, which lay within the agro-pastoral ecotone. We further explored the rules of landscape succession and the underlying natural and social mechanism, as well as the interactions between landscape types. Results showed that Wanjigou Village had been subjected to a succession from the landscape characterized by grassland, arable land and sandy land to that characterized by grassland, shrub land, sandy land and arable land. The change from the competition of landscape function separation to the preliminary integration had formed a definite succession path for grassland-arable land-sandy land-shrub land. The main driving factors were a synthesis of policy, human needs, and environment. Policy often promoted landscape change through large-scale and intensified human activities, while environment promoted landscape succession through internal driving force of ecosystem toward a mutual adaption between landscape and the innate conditions. The driving factors of landscape succession were soil moisture variations caused by the change of soil physical structure, and vegetation change in adapting to new environment. In agro-pastoral ecotone with low resource density, the separation of landscape functions was one of the main reasons for land desertification. The integration and coordination of landscape functions greatly alleviated the situation of ecological deterioration. The critical path to maintain sustainable development of agro-pastoral ecotone was to achieve complementation among landscape types and even integrating with external resources by transforming landscape separation competition into landscape symbiosis.

Study of Spatiotemporal Changes and Driving Factors of Habitat Quality: A Case Study of the Agro-Pastoral Ecotone in Northern Shaanxi, China

Habitat quality is a key indicator for assessing the biodiversity-maintenance functions of ecosystem services. The issue of habitat quality changes in semi-arid and arid areas has been becoming serious, but there are few deep investigations of habitat quality in these regions, such as studies of the temporal and spatial changes of habitat quality and its driving forces. This study focuses on the agro-pastoral ecotone of northern Shaanxi with vulnerable biodiversity. By using the Fragstats software, the InVEST model, and the Geo-detector model, we analyzed land-use data collected from 1990, 2000, 2010, and 2020, and we explored the landscape pattern index, the spatial and temporal variation of habitat quality, and the influence of its drivers. GDP, population density, precipitation, temperature, land use, NDVI, elevation, and slope were detected by Geo-detector. The research results show that: (1) Arable land and grassland were the dominant land types from 1990 to 2020, and there was significant mutual circulation between arable land and grassland. Forest area increased by 24%. Many other land-use types were transformed into construction land, and construction land increased by 727% compared with the base period. (2) Landscape heterogeneity increased in the study region, shown by the fractured structure of the overall landscape and by the aggravated human disturbance of the landscape. (3) Average habitat quality underwent a trend of oscillation. Regarding spatial distribution, habitat quality was higher in the east than in the west. (4) The influencing factors of habitat quality monitored by Geo-detectors show that the driving force of land use on habitat quality was the strongest, followed by precipitation and vegetation coverage. Elevation, slope, GDP, and population density had the least influence on habitat quality. The bi-factor interaction enhanced habitat quality to different levels. This study is critical to the conservation of biodiversity and to ecological civilization construction in arid and semi-arid regions.

Expansion of irrigation led to inland lake shrinking in semi-arid agro-pastoral region, China: A case study of Chahannur Lake

Study regionChahannur Lake, an inland lake of the Inner Mongolia Plateau, is located in the typical agro-pastoral ecotone, China. Study focusChange of lake area is highly sensitive to climate change and human activities, but the internal driving mechanism so far remains unclear. In this study, the spatiotemporal distribution of Chahannur Lake over the past 30 years was accurately extracted using the NDVI data, and the corresponding driver analysis was conducted. New hydrological insights for the regionBefore 2000, Chahannur Lake was always remaining watery state throughout the year and the maximum area reached 90 km2; however, after 2000 it became a seasonal lake with a long-term dry state. During the observed period, the recovery of water body had only occurred in two stages both of which belonged to historically heavy rain years, and the maximum lake area was only 40 km2. Although the climate has tended to be warm and humid after 2000, it cannot completely reverse the lake’s drying. Additionally, the irrigated arable increased by 392 km2 in 2000–2017, and the increased arable consumed substantial groundwater for meeting agricultural demands, which consequently caused rapid shrinkage of the Lake. Notably, the increase of NDVI is widely distributed in irrigated arable with high water-consuming crops. Overall, groundwater over-exploitation and strong water consumption from crops have jointly led to the drying of Chahannur lake.

How land-use change affects soil respiration in an alpine agro-pastoral ecotone

Land-use change alters soil carbon (C) storage in terrestrial ecosystem through affecting soil respirations (Rs). However, the long-term effects of land-use change on Rs are poorly understood. We undertook a field experiment to examine the effects of long-term land-use change on Rs. The land-use types included grazed grassland (GGL), enclosed grassland (EGL), continuous cropland (CCL), rotation cropland (RCL) and abandoned cropland (ACL) in an alpine agro-pastoral ecotone in Qinghai-Tibetan Plateau in China. Our results showed that the accumulative Rs was shown a decreasing order of EGL > CCL > RCL > GGL > ACL, with the highest value of 12.2 t CO2 ha−1 and the lowest value of 5.3 t CO2 ha−1. Soil bulk density, moisture, pH and C/N ratio were the key factors regulating Rs with land-use change in Tianzhu alpine agro-pastoral ecotone. Soil pH and C/N ratio regulated Rs indirectly by affecting bacterial diversity, while soil moisture had indirect impacts on Rs mainly by regulating microbial biomass. The net effects of soil bulk density on Rs was mainly through the direct pathway. Considering the soil C stocks showed an increasing order of ACL < RCL < CCL < GGL < EGL, even though ACL had the lowest Rs, grasslands probably the favorable land-use type in alpine agro-pastoral ecotone. Our findings highlight the importance of the land-use change on Rs, which may need to be incorporated into regional and global models for better predicting C-climate feedbacks.