Northeast Region Of China Research Articles

基于发生指数的中国森林生物灾害趋势与突变特征

PDF HTML阅读 XML下载 导出引用 引用提醒 基于发生指数的中国森林生物灾害趋势与突变特征 DOI: 10.5846/stxb202110132891 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中国林业科学研究院基本科研业务费专项（CAFYBB2016SY014，CAFYBB2020ZD001） Trend and abrupt change analysis of forest biological disasters in China based on forest pest outbreak index Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:监测分析森林生物灾害时空变化特征对了解森林生物灾害的动态演变和综合治理具有重要意义。基于1998-2019年森林有害生物灾害面积及同期森林面积增长统计数据，计算衍生了森林有害生物发生指数（FPOI）、灾害发生率（FPOAR）两个系列指标集，分别采用Sen's斜率估计（Sen+Mann-Kendall）和曼-肯德尔（Mann Kendall，M-K）突变检验、滑动T检验、变异系数和赫斯特指数（Hurst exponent）指数方法分析中国森林生物灾害的时空分异特征。研究表明：（1） FPOI、FPOAR指标用于森林生物灾害不同尺度分析具备可操作与适用性，两指标均可分析有害生物发生趋势与突变，但表现程度有所差别。（2）历史变化特征，全国尺度FPOI森林生物灾害总体表现为下降趋势，FPOAR表现为上升趋势，省区尺度，新疆、西藏、天津等局部省区森林生物灾害呈上升趋势，而华北、东北、华东、西北等大部分省区表现为下降态势。（3）突变特征，全国尺度上趋势突变仅在2001年发生，其它年度趋势未变。在省区尺度则大部分区域并未展现突变，局部省区多展现一次趋势改变，且不同省区突变时间有一致性。（4）稳定性特征，全国大部分省区显示稳定，但FPOI、FPOAR指标衡量存在差异，以FPOAR指标海南、青海、浙江、重庆、上海等5省区表现不稳定，但以FPOI指标，不稳定区域扩大到11省区，增加了除以上省区的甘肃、西藏、山西、河南、江苏、吉林6省区。（5）未来趋势特征，全国森林生物灾害与历史趋势保持一致，大部分省区呈现持续下降趋势。局部省区如新疆、西藏仍然显示持续增加态势。 Abstract:Monitoring and analyzing the spatio-temporal patterns changes is of great significance for understanding the dynamic evolution and integrated management of forest biological disasters. Based on the open statistical data of forest pest disaster area and forest cover area at national and provincial scale from 1998 to 2019, two series of indicators, the Forest Pest Outbreak Index (FPOI) and the Forest Pest Occurrence Area Rate (FPOAR), were calculated and derived. The spatial and temporal differentiation characteristics of forest biological disasters in China were revealed by the indicators data analysis with various methods. Sen's Slope Estimator and Mann Kendall test, Mann Kendall mutation test, sliding T test, coefficient of variation, and Hurst exponent were adopted separately in analyzing the trend, sudden changes and stability of occurred disasters. The results are as follows:(1) Both of FPOI and FPOAR indicators are suitable for different scales analysis of forest biological disasters. With the clearly differentiation of the consistent spatio-temporal data of the two indicators, the characteristics of forest biological disasters could be analyzed and quantitative visualized. However, there might be partially different between the results by the two indicators. (2) Regarding the characteristics of historical trend, the FPOI indicator with more weight on severe and moderate disasters showed downward trend at the national scale, while the FPOAR indicator was an upward trend. At the provincial scale, both indicators disclosed that forest biological disasters in Xinjiang, Tibet, Tianjin and a few other provinces were on the rise. However, more provinces in most regions of North, Northeast, East, and Northwest China showed a downward trend. (3) In terms of mutation characteristics, at the national scale, the trend mutation occurred only in 2001, and there was no mutation in other years. At the provincial scale, most regions did not show abrupt changes, and a few provinces showed one trend changes in the same years. (4) According to the stability characteristics of forest biological hazards, forest pest disasters showed stable in most provinces across the country. The performance of 5 provinces included Hainan, Qinghai, Zhejiang, Chongqing, Shanghai were unstable by the FPOAR indicator, the unstable provinces numbers expanded to 11 by the FPOI indicator, 6 more provinces included Gansu, Tibet, Shanxi, Henan, Jiangsu, Jilin provinces were joined. (5) For the characteristics of the future trend, forest pest disasters at the national scale and in regions at the provincial scale are consistent with historical trends, showing a continuous downward trend in most provinces. A few provinces, such as Xinjiang and Tibet, still show a continuous upward trend. 参考文献 相似文献 引证文献

Response of Physiological Growth Characteristics of Rice to Different Biodegradable Mulching and Irrigation Methods in Cold Region of Northeast China

Highlights The tested biodegradable mulch film can be rapidly degraded in rice fields in cold regions and has good applicability. The degradation rate of white mulch film is faster than that of black film before the induction period, and the degradation law after the induction period is opposite. The combination of mulching film and water-saving irrigation can effectively enhance the photosynthetic capacity and dry matter transport of rice in cold regions. Through comprehensive evaluation, we found that the combination of ridge irrigation and mulching FC plastic film has the best effect on environmental protection and rice growth. Abstract. To reveal the mechanism of influence of different types of biodegradable plastic film mulching and irrigation combinations on the physiological growth characteristics of rice in cold regions, eight types of film mulching irrigation methods were designed, which combined four types of plastic film mulching and two types of irrigation methods for a total of nine treatments. The study analyzed the degradation law of degradable plastic film in rice fields in cold regions, and the effects of film-mulching irrigation methods on rice photosynthetic characteristics, dry matter transport, and rice yield. The results showed that the three biodegradable plastic films were suitable for the rice fields in the northeast cold region. Except for the jointing stage, mulching irrigation treatments could increase the chlorophyll content and net photosynthetic rate of rice, and the improvement degree showed a downward trend with the growth of rice. The film mulching irrigation treatments improved rice stems and leaves dry matter transport and grain contribution. The comprehensive evaluation based on the comprehensive index method showed that the combination of ridge irrigation and thin black biodegradable mulch is the best combination of biodegradable plastic film mulching and irrigation in the study area. Keywords: Biodegradable mulching, Comprehensive index method, Dry matter transportation, Irrigation method, Photosynthetic character.

Nutrient retranslocation strategies associated with dieback of Pinus species in a semiarid sandy region of Northeast China

In the semiarid sandy region of Northeast China, Mongolian pine (Pinus sylvestris var. mongolica) suffers dieback after the age of 35, while Japanese red pine (Pinus densiflora) and Chinese pine (Pinus tabuliformis) stay healthy. Foliar nutrient retranslocation reflects the nutrient conservation and utilization mechanism of plants in response to their habitats. However, the nutrient retranslocation strategies employed by three Pinus tree species to cope with nutrient limitations remain largely unknown. For this study, we investigated the seasonal variations in nitrogen (N) and phosphorus (P) concentrations of Mongolian pine, Japanese red pine, and Chinese pine plantations in terms of the green needles of all ages, senesced needles, and soil. Further, the N retranslocation efficiency (NRE), and P retranslocation efficiency (PRE), and correlations between the N:P ratios of needles and soil were analyzed. The results showed that, except for the spring NRE in 1-year-old needles of Mongolian pine, the spring NRE and PRE in 1- and 2-year-old needles of the three tree species were greater than zero. The autumn PRE was higher than zero for Mongolian pine, but lower than zero for Japanese red pine and Chinese pine. Among the three Pinus species, Mongolian pine showed greater spring PRE in 2-year-old needles, and PRE from 1- to 2-year-old needles, and from 2-year-old needles to litter. However, Japanese red pine had higher P concentrations and lower N:P ratios in senesced needles, while greater PRE was found in Chinese pine litter. Significant relationships between the N:P ratios were found in the current year and 1-year-old needles and soil in the Mongolian pine plantation, while there was an insignificant relationship between the N:P ratios of the needles and soil in the Chinese pine plantation. Thus, for Mongolian pine, the removal of P from needles in autumn, and higher P translocation from older needles under P-deficient soil may have contributed to the tree dieback. In contrast, Japanese red pine and Chinese pine stored P in their needles during autumn. Japanese red pine returned more P to the soil via litter, while Chinese pine maintained N:P homeostasis and increased P withdrawal prior to needle abscission.

Spatiotemporal changes of cultivated land use system resilience in the black soil region of Northeast China under food supply security: A case study of Qiqihar City

Spatiotemporal changes of cultivated land use system resilience in the black soil region of Northeast China under food supply security: A case study of Qiqihar City

Spatial and temporal changes of erosion in the black soil region of Northeast China from 2000 to 2020

Spatial and temporal changes of erosion in the black soil region of Northeast China from 2000 to 2020

Responses of nutrient resorption to interannual precipitation variability and nitrogen addition in a pine plantation

AbstractPlant nutrient concentration and resorption play a major role in determining primary production and development of forests. Yet how plant nutrient concentration and resorption respond to altered interannual precipitation and how interannual precipitation variability mediates the responses of plant nutrient concentration and resorption to N addition remain uncertain. Here, we examined the responses of needle nutrient (N and P) concentrations of all aged classes, nutrient resorption efficiency, and proficiency to N addition (10 g N m−2 year−1) over a 4‐year period (from 2016 to 2019) that experienced high variability in precipitation in a Mongolian pine plantation in a semiarid region of northeast China. There were significant interannual variations in N and P concentrations in all aged needles and litters, N and P resorption efficiency, as well as soil inorganic N and available P concentrations in the control plots. Increased precipitation resulted in increased needle nutrient concentrations across the four consecutive years. However, needle nutrient concentrations did not covary with soil available nutrients. The responses of needle N resorption efficiency (NRE) to N addition differed across the four years, with N addition decreasing NRE in wet years, but not in dry years. Taken together, our results showed that foliar nutrient concentrations are sensitive to altered annual precipitation and that different interaction effects exist between N addition and sampling year for different nutrient variables. Such differential responses highlight the challenge of predicting effects of N addition on nutrient cycling over temporal scales.

Differential Analysis of Biochar Effects on Soil Physicochemical Properties

For a long time, because of China’s large population and small per capita resource occupancy, the use of natural resources is unreasonable. Soil degradation problem due to the long-term irrational utilization of land resources is becoming more and more serious, which seriously damaging the ecological environment and hindering China’s modernization process. Facing the problem of soil remediation, biochar technology has become a research hotspot because of its advantages of green environmental protection, low cost, high efficiency, and wide application. And black soil in northeast China and southern region of red soil as important soil types of agroforestry in China, over the years have experienced serious soil degradation crisis. In this paper, black soil and red soil are selected as research objects to explore the impact of biochar on the physical and chemical properties of the two soils. This paper intends to use the methods of investigation and analysis, and comparison in many aspects. Through the study, it was found that the application of biochar had the same trend of influence on the organic carbon content and C/N ratio of the two soils, but the index of black soil increased more significantly. The change trend of soil bulk density and pH was also consistent with the application of biochar, and the difference was not significant. The effects of biochar applied to the two soils on greenhouse gas emissions were quite different. The soil health of black soil and red soil is of great significance in China’s agricultural production and life. This paper expects to bring reference value to the improvement of the overall soil function and the promotion of ecological restoration process of China’s biochar modification work for different soil types in the north and south, by comparing the impact of biochar on the physical and chemical properties of the two soils. A better soil improvement program can be obtained after comparative analysis, so as to provide suggestions on sustainable development and comprehensively promote ecological construction.

Spatio-Temporal Evolution of the Ecological Environment in a Typical Semi-Arid Region of Northeast China

Increasing trends of groundwater and soil salinization, as well as desertification, is characteristic of many arid and semi-arid regions under climatic and anthropogenic influences. This has led to the implementation of management strategies to protect the ecological environment. Changling County in Northeast China is a typical semi-arid area that has experienced these changes. Thus, management strategies such as the “Three North Shelterbelt Project” which involves planting trees to reduce wind speed and halt desertification, and the Changling local alkaline land restoration project, from the year 2000, involving fencing of grasslands have been implemented in the area. Premised on the dynamic nature of the ecological environmental problems, this study was undertaken to assess the spatio-temporal evolution of the ecological environment using hydro-geochemical, spatial, remote sensing, and statistical techniques from the year 2001 to 2019. It was found that groundwater salinity was stable within the period due to groundwater exploitation that declined depth to groundwater table (DWT) thus reducing the impact of evaporation concentration of salts in groundwater. Salinized land area increased by about 6706 ha at a rate of 0.06%/year as a result of the reduction in the size of water bodies and swampland as the declining water table exposed shallow water to more evaporation. The effect of the conversion of water bodies and swamplands to salinized land is believed to overshadow the climatic influence of decreased evaporation-precipitation ratio that normally decreases soil salinization. Most of the study area was stable in terms of desertification (98.22%, 56,3497 ha) as significantly degraded lands covered only 0.03% (148 ha) of the area while 1.67% (9556 ha) had significantly increased vegetation, respectively. Precipitation had an insignificant relationship with desertification with irrigation believed to be the main driver of significant vegetation improvement. Water-saving irrigation practices and the growing of salt-tolerant or semi-tolerant crop species are recommended to maximize food production while stemming the environmental degradation trend due to declining DWT.

Effects of grain-forage crop type and natural rainfall regime on sloped runoff and soil erosion in the Mollisols region of Northeast China

Clarifying the responses of runoff and soil erosion to crop type and rainfall regime is important for the optimization of crop planting systems and land use and management. This study was conducted to quantify the effects of five grain-forage crop types and rainfall regimes on sloped runoff generation and soil loss, and to further identify the factors influencing runoff and soil erosion in Mollisols region of Northeast China. Runoff and soil loss were monitored from 24 runoff plots including wheat, corn, soybean, alfalfa, and bromegrass, with the bare land as a control. 31 erosive rainfall events were classified into three rainfall regimes: regime Ⅰ with low precipitation (P) and duration (D), moderate intensity (I30) and frequent occurrence; regime Ⅱ with moderate P, long D and low I30; and regime III with high P and I30, moderate D and less frequent occurrence. Soil loss caused by regime III was 3.61–12.93 times greater than that under regimes Ⅰ and Ⅱ. Five crops reduced runoff and soil loss by 21.5%-69.3% and 54.1%-77.0%, respectively, of which bromegrass showed the highest reduction, especially the reductions of alfalfa and bromegrass under regime III, which were significantly higher than those of the three grain crops. Wheat showed a higher runoff reduction than soybean and corn but its soil loss reduction was lower due to harvest in mid-July. Crop type greatly influenced the correlations between runoff and soil erosion and rainfall and plant properties. Changes in runoff were significantly related to P, rainfall erosivity (EI30), coverage, plant height and root density, and the variations in soil erosion were dominated by runoff depth, D, EI30, and coverage. Path analysis showed that the rainfall and runoff properties produced larger influences on runoff depth and soil loss rate than plant traits. More attention should be paid to rainfall regime III, and grain and forage crops with shorter stems and higher coverage and earnings are preferred.

Heat storage and release performance experiment of externally hung phase change solar greenhouse in severe cold regions of Northeast China - Taking Fuxin City as an example

The traditional solar greenhouses in severe cold regions of northeast China have poor heat storage and thermal insulation performance, and the abundant solar energy resources cannot be utilized rationally. Phase change energy storage is considered to be one of the effective ways to cope with this problem. The price, encapsulation leakage and arrangement of PCM are the bottleneck problems restricting its practical application. This paper used the modified calcium chloride hexahydrate-based phase change material as the energy storage medium. A PVC-U tube was used for encapsulation and external hanged on the inner surface of the north wall of the partitioned greenhouse. Based on the 51 days of field comparison test, the comparative greenhouse heat storage and release performance under typical sunny, cloudy and snowy conditions was discussed. Through the experiments, it was found that the externally hung phase change energy storage device increased the effective accumulated temperature by 21.1 %, changing the dynamic heat transfer relationship between the envelope structure and indoor air. It confirmed the feasibility of promoting the externally hung phase change energy storage device in the severe cold region of Northeast China.

Variability in mollic epipedon thickness in response to soil erosion–deposition rates along slopes in Northeast China

The Mollisol region of Northeast China is one of the most significant grain-producing areas. Intense soil erosion has led to a sharp decline in both the mollic epipedon (ME) thickness and soil quality, and these processes have in turn resulted in a serious threat to the national food security. Soil erosion–deposition processes influence the soil thickness. However, the quantitative relationship between the ME thickness and soil erosion–deposition rate along slopes remains unclear. In this study, the ME thickness and soil erosion–deposition rate along three typical long, gentle slopes in Heilongjiang Province were investigated by using ground-penetrating radar (GPR) and 137Cs tracing technology. Variations in the spatial characteristics of the ME thickness and soil erosion–deposition rate on slopes were obtained. Wavelet analysis was employed to analyse the soil erosion–deposition rate on these slopes. The results indicated that the soil erosion rate along the three slopes was periodic and oscillated between high and low values. The range of primary cycle variation was 73–80 m, and the range of secondary cycle variation was 44–47 m. A negative correlation was found between the soil erosion–deposition rate and ME thickness within each cycle. The periodic variability in the soil erosion rate on these slopes also yielded a periodic variability in the ME thickness. Fitted equations were derived based on the ME thickness, slope length and soil erosion–deposition rate. The error range for soil thickness prediction was 0.30–9.40 %. This study could provide an efficient and accurate method to predict ME thickness change patterns along slopes and to help arrange soil erosion control measures at appropriate locations.

Soil Anti-Scourabilities of Four Typical Herbaceous Plants and Their Responses to Soil Properties, Root Traits and Slope Position in Northeast China

Vegetation has been proven to be an effective measure to mitigate soil erosion in most regions and climates. However, it is not clear how some herbaceous plants affect the ability of soil to resist slope flow erosion in the Mollisol region of Northeast China. In this study, four herbaceous plant plots of 50 m × 4.5 m, including Zea mays L., Sorghum bicolor × Sudanense, Avena sativa L. and Lolium multiflorum Lam., were established in a sloping land with an abandoned land as the control to detect the effect of herbaceous plants on soil anti-scourability (ANS). A hydraulic flume experiment was carried out to determine the soil ANS, and the root traits and soil properties were also measured at different slope positions. The results showed that the mean soil ANS ranged from 17.55 to 94.77 L g−1 among different herbaceous plants, of which the Lolium multiflorum Lam. showed the strongest controlling effect on soil ANS (259.87%), followed by Sorghum bicolor × Sudanense (66.87%) and Avena sativa L. (18.12%), while the soil ANS of Zea mays L. decreased by 33.37% compared with the control. Soil ANS varied with slope position, and the mean soil ANS at the upslope was 116.50–134.21% higher than that of the middle slope and downslope. Additionally, soil ANS was positively related to root mass density (RMD), root length density (RLD), root surface area density (RSAD), soil total porosity and field capacity but was negatively related to soil bulk density (p < 0.05). Furthermore, the Lolium multiflorum Lam. exhibited better root distribution (i.e., high RSAD, RLD, RMD, and low root diameter) and soil physical structure (i.e., high soil porosity structure, water-holding capacity and low bulk density) than other plant species. Thus, the Lolium multiflorum Lam. is beneficial for enhancing soil erosion resistance to overland flow, especially at the up and middle slopes, and it could be preferred to control sloped soil erosion in Northeast China.

Enrichment characteristics of potential risk elements in the black soil region of Northeast China

Heavy metals in topsoil mainly originate from the natural geological background and human activities, and once the soil is contaminated with heavy metals, it is difficult to restore it to its original natural state. Therefore, it is important to assess the level of influence of heavy metals in soil to provide information for agricultural production. To clarify the intensity of anthropogenic impact on the soil environment in the black soils region (BSR), we used the geochemical data of 0–20cm topsoil (anthropogenic impact depth) and 150–180cm subsoil(natural background) to analyze the topsoil heavy metal enrichment coefficient for cadmium, mercury, lead, arsenic, zinc, nickel, copper, chromium, and their spatial distribution characteristics in BSR . The analysis showed that the heavy metal enrichment coefficients of lead, arsenic, zinc, nickel, copper and chromium are basically less than 2.0 in BSR, and there are only localized points with enrichment coefficients of greater than 2.0. Cadmium and mercury are more obviously enriched in the black soils area, and the enrichment areas are mainly distributed south of Harbin. The mercury enrichment area is distributed in a north–eastward strip along Shenyang, Changchun, and Harbin, and the cadmium enrichment areas are mainly distributed south of Changchun, with a continuous distribution to Tieling City. the enrichment of heavy metals in the topsoil is closely related to the population density by comparing spatial distribution patterns of the geological background, topography and land use, and the obvious enrichment areas for heavy metals are located in and around cities, especially in industrial cities and their surrounding areas. The enrichment depth of 40 cm is further evidence that the heavy metals in topsoil mainly originate from human activities.

Improving nitrogen contribution in maize post-tasseling using optimum management under mulch drip irrigation in the semiarid region of Northeast China.

Film-mulched drip irrigation has become an important strategy in maize cultivation in the semiarid region of Northeast China. Most farmers concentrate nitrogen (N) fertilizer use early in maize growth, which leads to low N use efficiency and large N losses. Therefore, a three-year (2018 to 2020) field experiment was conducted to determine the optimal N management strategy for maize under film mulch with drip irrigation in the semiarid region of Northeast China. The experiment included five treatments with the total amount of N fertilizer (210kg N ha-1) applied in different proportions at sowing, sixth-leaf (V6), twelfth-leaf (V12), tasseling (VT), and blister (R2) stages of maize growth: N1, 100-0-0-0-0; N2, 50-50-0-0-0; N3, 30-50-20-0-0; N4, 20-30-30-20-0; and N5, 10-20-30-20-20. The control (CK) did not receive N fertilizer. Maize yield, N uptake and use, changes in soil inorganic N content, and N balance were investigated. Compared with the single basal application (N1), split-N applications (N2, N3, N4, N5) increased maize yield from 13.8% to 24.5% by increasing kernel number per ear and 1000-kernel weight and also improved N accumulation from VT to physiological maturity (PM) stages and its contribution to grain N uptake. In addition, compared with N1, split-N applications also decreased N losses by increasing inorganic N contents in the 0-40 cm soil layer and by decreasing N leaching in the 60-200 cm soil layer. Regression analysis demonstrated that N accumulation after the VT stage was positively related with maize yield. Among treatments, N4 had the highest yield, N recovery efficiency, agronomic efficiency, and partial factor productivity, with respective increases of 24.5%, 14.7 percentage point, 11.4kg kg-1, and 11.4kg kg-1 compared with those in N1. As a result, N losses were also reduced by 33.7% in N4 compared with those in N1. In conclusion, the split-N management strategy with four N applications under film-mulched drip irrigation has great potential to improve maize yield, increase N use efficiency, and reduce N loss in the semiarid region of Northeast China.

Temporal and spatial changes in soil organic carbon and soil inorganic carbon stocks in the semi-arid area of northeast China

Soil organic carbon (SOC) and soil inorganic carbon (SIC) has important effects on soil physical, chemical and biological properties. They play an important role in coordinating the relationship between soil water and air, increasing soil water holding capacity and improving plant productivity. In this study, a boosted regression trees (BRT) model was developed to map the spatial distribution carbon stocks in the semi-arid region of Northeast China in 1990 and 2015. During the two periods, 10-fold cross-validation technology was used to test the performance and uncertainty of BRT model. In order to construct the model, 9 environmental variables (derived from climate, topography and biology) and 173 (1990) and 223 (2015) topsoil (0–30 cm) samples were used. The comparison between estimated and observed data shows that the RMSE of SOC and SIC stocks were 0.53 kgm−2 and 0.19 kgm−2 in 1990, and 0.65 kgm−2 and 0.20 kgm−2 in 2015, respectively. Elevation, normalized difference vegetation index, mean annual precipitation and Landsat band 3 were identifies as critical environmental factors for simulating the spatial distribution of SOC, accounting for 76.6 % and 70.3 % of the total relative importance in 1990 and 2015, respectively. Mean annual precipitation, mean annual temperature and topographic wetness index were the critical environmental factors for simulating the spatial variation of SIC during the two periods. Land use change also played an important role in the spatial variability of SOC and SIC stocks. In the past 25 years, soil carbon stocks decreased from 6.2 kg m−2 in 1990 to 5.9 kg m−2 in 2015. The spatial distribution pattern of SOC was high in northeastern area and low in southwestern area during the two periods, while the spatial distribution pattern of SIC was opposite to that of SOC stocks. The mapped soil carbon stock distribution is fundamental to future study of soil carbon cycle and regional carbon balance in semi-arid regions.

Spatio-temporal variations and drought of spring maize in Northeast China between 2002 and 2020.

A lot of spring maize is grown in Northeast China (Liaoning, Jilin, and Heilongjiang), an area that is highly susceptible to drought. Here, remote sensing indexes from 2002 to 2020 were studied using the 8-day surface reflectance and land surface temperature of Moderate-resolution Imaging Spectroradiometer data. Spring maize distribution was extracted using a decision tree classification, and the results were compared to the known distribution based on field investigation data and published statistics. The results showed that mixed pixels of spring maize and soybeans had limited influence on the study of spatio-temporal variations of spring maize, and the error was acceptable. The overall accuracy of verifying the spring maize distribution from 2018 to 2020 was above 85%. The stable, fluctuating, and low-frequency planting areas of spring maize accounted for 11.86%, 17.41%, and 34.86% of the study area, respectively. In 2015, the government directed a reduction of the planting area of spring maize in the "Liandaowan" region of Northeast China. The planting area of spring maize was characterized by a continuous increase before this change (2002-2014), exhibited changes and reductions in response to the change (2015-2017), and exhibited optimization and recovery after this change (2018-2020). Compared with the fluctuating and low-frequency planting areas, moderate and severe droughts were higher in stable planting areas. From 2002 to 2020, the most severe droughts occurred in the expanded planting areas. This rapid and large-scale monitoring of spatio-temporal variations and drought of spring maize provides a foundation for improving grain yield. This method could be easily applied to the study of other regions and combined with high-resolution and hyperspectral satellite data to improve monitoring accuracy.

Large-Scale Renewable Energy Transmission by HVDC: Challenges and Proposals

Renewable energy transmission by high-voltage direct current (HVDC) has attracted increasing attention for the development and utilization of large-scale renewable energy under the Carbon Peak and Carbon Neutrality Strategy in China. High-penetration power electronic systems have gradually formed at the sending end of HVDC transmission. The operation of such systems has undergone profound changes compared with traditional power systems dominated by synchronous generators. New stability issues, such as broadband oscillation and transient over-voltage, have emerged, causing tripping accidents in large-scale renewable energy plants. The analysis methods and design principles of traditional power systems are no longer suitable for HPPESs. In this paper, the mechanisms of broadband oscillation and transient over-voltage are revealed, and analytical methods are proposed for HPPESs, including small-signal impedance analysis and electromagnetic transient simulation. Validation of the theoretical research has been accomplished through its application in several practical projects in north, northwest, and northeast region of China. Finally, suggestions for the construction and operation of the future renewable-energy-dominated power system are put forward.

Gully erosion susceptibility assessment based on machine learning-A case study of watersheds in Tuquan County in the black soil region of Northeast China

Owing to its unique topographic and climatic conditions, agricultural production, and anthropogenic grazing, severe gully erosion has developed in the watersheds of Tuquan County located in the black soil region of Northeast China. Using three machine learning models to assess gully erosion susceptibility in this region, the main purpose of this study was to determine the important factors affecting the occurrence of gully erosion from 25 geo-environmental factors and select the model with the best prediction performance. Field data collection was conducted for 823 gullies. 12,496 pixels corresponding to 823 gullies and 12,496 pixels without gully erosion were randomly selected to form the model calculation database. According to the principle of multiple screening, this study selected 25 geo-environmental factors affecting the occurrence of gully erosion. Two factors, coarse sand content and fine sand content, were excluded by multi-collinearity analysis and using random forest (RF), convolution neural network (CNN), and transformer models, combining the 10-fold cross-validation and related validation metrics to assess the susceptibility of gully erosion in Tuquan County’s small watersheds. The results show that the convergence index (CI), topographical wetness index (TWI), terrain ruggedness index (TRI), and distance from the river based on the RF model are important factors affecting the occurrence of gully erosion. The transformer model (mean AUC of training = 95.338 %, mean AUC of validation = 95.342 %) was superior to the RF (mean AUC of training = 99.997 %, mean AUC of validation = 92.518 %) and CNN (mean AUC of training = 86.995 %, mean AUC of validation = 84.647 %) models in predicting performance. To ensure that the management and decision-making departments take reasonable and effective measures to prevent gully erosion in the study area, the gully erosion susceptibility maps produced using the three machine learning models were beneficial.

Prospects of sediment deposition at small watershed scale in the black soil region of Northeast China: A mini review

Sediment deposition is one of the most significant processes in small watersheds characterized by gentle long hillslopes in the black soil (Mollisol) region of Northeast China, as indicated by severe ephemeral gully and gully erosion on hillslopes and very low sediment concentrations in river systems. Few reviews have been conducted to summarize the related research in this region. The objectives of this review were to identify the potential factors influencing sediment deposition, review related studies, and propose future research needs in the black soil region of Northeast China. Sediment deposition is controlled by the deficit between sediment transport capacity of flow and sediment load. Hence, all factors affecting flow transport capacity and sediment load directly affect sediment deposition. For a specific small watershed, the change in slope gradient along the flow path is the key factor affecting sediment deposition. Shelterbelts, ridge tillage systems, terraces, grass strips, road distribution, ponds and reservoirs, and land-use patterns also influence the spatial distribution and rate of deposition. The trace method has been widely used to quantify sediment deposition in this region. The results of cesium-137 (137Cs), lead-210 (210Pb), and magnetic susceptibility reveal that serious deposition occurs on the back and foot slopes. Distinct deposition occurs in front of contour shelterbelts. Future studies should focus on the methodology, spatial and temporal variations, dominant influencing factors and their mechanisms, and the potential effects on land productivity within specific small watersheds and across the black soil region. This review provides insights into the sediment deposition process in small watersheds characterized by gentle, long hillslopes.

Spatial–Temporal Evolution Patterns and Regulatory Strategies for Land Resource Carrying Capacity of China’s Major Grain-Producing Areas

Research on land resource carrying capacity (LRCC) focuses on the population that regional land resources can support as well as the grain output they can deliver. China’s major grain-producing areas consist of 13 provinces, and the grain produced in these areas makes up 75% of the country’s gross grain output. To boost the land carrying capacity of major grain-producing areas and to ensure national food security, it is crucial to examine the spatial–temporal evolution patterns of LRCC and to devise optimal regulatory strategies. From the perspective of human–grain relationships, this paper looks into the evolutionary features of the spatial–temporal patterns of the LRCC of China’s major grain-producing areas based on a land resource carrying capacity model, a land resource carrying capacity index model, and a land resource limitation model. We obtain three main results: (1) On the temporal scale, the land resource carrying capacity index (LRCCI) of China’s major grain-producing areas as a whole tapered off over a period from 1980 to 2020, whereas the overall LRCC increased in this period, indicating that the human–grain relationship in China’s major grain-producing areas is improving. (2) On a spatial scale, China’s major grain-producing areas ranked by LRCC from the greatest to the lowest, in 2020, were North China, the middle and lower reaches of the Yangtze River, Northeast China, and other regions. In terms of the carrying state of land resources, provinces with grain surpluses significantly rose during 1980–2020, the growth of LRCC of the aforementioned four major regions markedly slowed down in 2015–2020, and a large gap exists in LRCCI between the 13 provinces, revealing an unbalanced, insufficient development of LRCC in each province. (3) From 2000 to 2020, the limit of land resources on population aggregation in most major grain-producing areas was negative, and its absolute value continued to increase; this suggests that the land resources of major grain-producing provinces set small limits on population aggregation, with great potential for increasing LRCC. Taking into account the research results, this paper gives strategies for regulating the LRCC of China’s major grain-producing areas in a bid to further augment the human–grain carrying capacity of land resources in China’s major grain-producing areas and to guarantee national food security.