准格尔露天矿区复垦对土壤细菌多样性的影响研究

运用PCR-DGGE技术对我国准格尔露天煤矿不同复垦时间土壤细菌组成及其多样性变化进行了研究,结果表明:1)复垦区的土壤细菌主要是厚壁菌门、拟杆菌门、放线菌门、变形菌门、酸杆菌门、芽单胞菌门和未知细菌类7类,其中,放线菌门、拟杆菌门和变形菌门为优势类群,占到全部细菌的81.2%;2)成功完成矿山土壤样品微生物总DNA提取和PCR-DGGE的分析检测,在69个测序序列中,不可培养细菌占到总数的62.3%;3)各复垦阶段存在共有细菌类群,但更多的细菌类群是随复垦时间不同而发生变化的。4)豆科-禾本科牧草种植区的土壤细菌多样性指数要高于乔灌草类型,这可能与豆科植物中丰富的根瘤菌利于土壤细菌生长发育有关。     

Arbuscular mycorrhizal fungi ameliorate the chemical properties and enzyme activities of rhizosphere soil in reclaimed mining subsidence in northwestern China

In semi-arid region of northwestern China, underground mining subsidence often results in decreased vegetation coverage, impoverishment of soil fertility and water stress. In addition, the physical-chemical and biological properties of soil also change, resulting in more susceptible to degradation. In particular, subsidence causes disturbance of the symbioses of plant and microbe that can play a beneficial role in the establishment of vegetation communities in degraded ecosystems. The objective of this study was to evaluate the effects of revegetation with exotic arbuscular mycorrhizal fungi(AMF) inoculum on the chemical and biological properties of soil over time in mining subsidence areas. Soils were sampled at a depth up to 30 cm in the adjacent rhizosphere of Amorpha fruticose Linn. from five reclaimed vegetation communities in northwestern China. In August 2015, a field trial was set up with five historical revegetation experiments established in 2008(7-year), 2011(4-year), 2012(3-year), 2013(2-year) and 2014(1-year), respectively. Each reclamation experiment included two treatments, i.e., revegetation with exotic AMF inoculum(AMF) and non-AMF inoculum(the control). Root mycorrhizal colonization, glomalin-related soil protein(GRSP), soil organic carbon(SOC), soil nutrients, and enzyme activities were also assessed. The results showed that mycorrhizal colonization of inoculated plants increased by 33.3%–163.0% compared to that of non-inoculated plants(P<0.05). Revegetation with exotic AMF inoculum also significantly improved total GRSR(T-GRSP) and easily extracted GRSP(EE-GRSP) concentrations compared to control, besides the T-GRSP in 1-year experiment and the EE-GRSP in 2-year experiment. A significant increase in SOC content was only observed in 7-year AMF reclaimed soils compared to non-AMF reclaimed soils. Soil total N(TN), Olsen phosphorus(P) and available potassium(K) were significantly higher in inoculated soil after 1–7 years of reclamation(except for individual cases), and increased with reclamation time(besides soil Olsen P). The exotic AMF inoculum markedly increased the average soil invertase, catalase, urease and alkaline phosphatase by 23.8%, 21.3%, 18.8% and 8.6%, respectively(P<0.01), compared with the control. Root mycorrhizal colonization was positively correlated with soil parameters(SOC, TN and soil available K) and soil enzyme activities(soil invertase, catalase, urease and alkaline phosphatase) in both AMF and non-AMF reclaimed soils(P<0.05), excluding availableK in non-AMF reclaimed soils. T-GRSP(P<0.01) and EE-GRSP(P<0.05) were significantly correlated with the majority of edaphic factors, except for soil Olsen P. The positive correlation between root mycorrhizal colonization and available K was observed in AMF reclaimed soils, indicating that the AMF reclaimed soil with a high root mycorrhizal colonization could potentially accumulate available K in soils. Our findings concluded that revegetation with exotic AMF inoculum influenced soil nutrient availability and enzyme activities in the semi-arid ecosystem, suggesting that inoculating AMF can be an effective method to improve soil fertility and support restoration of vegetation communities under poor conditions like soil nutrient deficiency and drought.     

Attribution analysis and multi-scenario prediction of NDVI drivers in the Xilin Gol grassland,China

Grassland degradation is influenced by climate change and human activities, and has become a major obstacle for the development of arid and semi-arid areas, posing a series of environmental and socio-economic problems. An in-depth understanding of the inner relations among grassland vegetation dynamics, climate change, and human activities is therefore greatly significant for understanding the variation in regional environmental conditions and predicting future developmental trends. Based on MODIS (moderate resolution imaging spectroradiometer) NDVI (normalized difference vegetation index) data from 2000 to 2020, our objective is to investigate the spatiotemporal changes of NDVI in the Xilin Gol grassland, Inner Mongolia Autonomous Region, China. Combined with 12 natural factors and human activity factors in the same period, the dominant driving factors and their interactions were identified by using the geographic detector model, and multiple scenarios were also simulated to forecast the possible paths of future NDVI changes in this area. The results showed that: (1) in the past 21 a, vegetation cover in the Xilin Gol grassland exhibited an overall increasing trend, and the vegetation restoration (84.53%) area surpassed vegetation degradation area (7.43%); (2) precipitation, wind velocity, and livestock number were the dominant factors affecting NDVI (the explanatory power of these factors exceeded 0.4). The interaction between average annual wind velocity and average annual precipitation, and between average annual precipitation and livestock number greatly affected NDVI changes (the explanatory power of these factors exceeded 0.7). Moreover, the impact of climate change on NDVI was more significant than human activities; and (3) scenario analysis indicated that NDVI in the Xinlin Gol grassland increased under the scenarios of reduced wind velocity, increased precipitation, and ecological protection. In contrast, vegetation coverage restoration in this area was significantly reduced under the scenarios of unfavorable climate conditions and excessive human activities. This study provides a scientific basis for future vegetation restoration and management, ecological environmental construction, and sustainable natural resource utilization in this area.     

Spatial-temporal dynamics of desert vegetation and its responses to climatic variations over the last three decades:a case study of Hexi region in Northwest China

Analysis of spatial-temporal variations of desert vegetation under the background of climate changes can provide references for ecological restoration in arid and semi-arid areas.In this study,we used the Global Inventory Modeling and Mapping Studies(GIMMS)NDVI data from 1982 to 2006 and Moderate Resolution Imaging Spectroradiometer(MODIS)NDVI data from 2000 to 2013 to reveal the dynamics of desert vegetation in Hexi region of Northwest China over the past three decades.We also used the annual temperature and precipitation data acquired from the Chinese meteorological stations to analyze the response of desert vegetation to climatic variations.The average value of NDVImax(the maximum NDVI during the growing season)for desert vegetation in Hexi region increased at the rate of 0.65×10–3/a(P0.05)from 1982 to 2013,and the significant increases of NDVImax mainly appeared in the typical desert vegetation areas.Vegetation was significantly improved in the lower reaches of Shule and Shiyang river basins,and the weighted mean center of desert vegetation mainly shifted toward the lower reaches of the two basins.Almost 95.32% of the total desert vegetation area showed positive correlation between NDVImax and annual precipitation,indicating that precipitation is the key factor for desert vegetation growth in the entire study area.Moreover,the areas with non-significant positive correlation between NDVImax and annual precipitation mainly located in the lower reaches of Shiyang and Shule river basins,this may be due to human activities.Only 7.64% of the desert vegetation showed significant positive correlation between NDVImax and annual precipitation in the Shule River Basin(an extremely arid area),indicating that precipitation is not the most important factor for vegetation growth in this basin,and further studies are needed to investigate the mechanism for this phenomenon.     

Potential responses of vegetation to atmospheric aerosols in arid and semi-arid regions of Asia

Changes in atmospheric aerosols have profound effects on ecosystem productivity, vegetation growth and activity by directly and indirectly influencing climate and environment conditions. However, few studies have focused on the effects of atmospheric aerosols on vegetation growth and activity in the vulnerable arid and semi-arid regions, which are also the source areas of aerosols. Using the datasets of aerosol optical depth(AOD), normalized difference vegetation index(NDVI) and multiple climatic variables including photosynthetically active radiation(PAR), surface solar radiation(SSR), surface air temperature(TEM) and total precipitation(PRE), we analyzed the potential responses of vegetation activity to atmospheric aerosols and their associated climatic factors in arid and semi-arid regions of Asia from 2005 to 2015. Our results suggested that areas with decreasing growing-season NDVI were mainly observed in regions with relatively sparse vegetation coverage, while AOD tended to increase as NDVI decreased in these regions. Upon further analysis, we found that aerosols might exert a negative influence on vegetation activity by reducing SSR, PAR and TEM, as well as suppressing PRE in most arid and semi-arid regions of Asia. Moreover, the responses of atmospheric aerosols on vegetation activity varied among different growing stages. At the early growing stage, higher concentration of aerosol was accompanied with suppressed vegetation growth by enhancing cooling effects and reducing SSR and PAR. At the middle growing stage, aerosols tended to alter microphysical properties of clouds with suppressed PRE, thereby restricting vegetation growth. At the late growing stage, aerosols exerted significantly positive influences on vegetation activity by increasing SSR, PAR and TEM in regions with high anthropogenic aerosols. Overall, at different growing stages, aerosols could influence vegetation activity by changing different climatic factors including SSR, PAR, TEM and PRE in arid and semi-arid regions of Asia. This study not only clarifies the impacts of aerosols on vegetation activity in source areas, but also explains the roles of aerosols in climate.     

榆林地区植被指数动态变化及其对气候和人类活动的响应

榆林地区是中国典型生态脆弱区,植被生态系统对气候变化和人类活动影响较为敏感。以榆林地区2000—2015年MODIS NDVI为基础,结合气温、降水数据,利用线性趋势法、相关系数、偏相关系数及缓冲区方法,分析了区域NDVI(归一化差异植被指数)动态变化及其对气候和人类活动的响应,结果表明:(1)榆林地区总体上NDVI较小,植被覆盖水平较低。2000—2015年NDVI以每年0.009 6的线性速率递增,空间上主要表现出线性增加趋势,占总面积的97.06%,减少趋势面积较小且主要与人类活动有关,分布在区域西南部山区、城镇附近及中、东部的河流谷地。(2)相关分析表明,榆林地区NDVI与气温以负相关为主,而与降水以正相关为主,反映出干旱、半干旱地区水分是植物生长的主导因子。(3)NDVI变化过程反映出人类活动范围中,市级行政中心缓冲区人类活动强度高于县级行政中心缓冲区。市级行政中心缓冲区范围可划分为5 km以内受人类活动剧烈影响区域、5~9km受人类活动影响递减区域和9 km以外未受人类活动影响区域。     

Vegetation dynamics of coal mining city in an arid desert region of Northwest China from 2000 to 2019

Coal mining has led to serious ecological damages in arid desert region of Northwest China. However, effects of climatic factor and mining activity on vegetation dynamics and plant diversity in this region remain unknown. Wuhai City located in the arid desert region of Northwest China is an industrial city and dominated by coal mining. Based on Landsat data and field investigation in Wuhai City, we analyzed the vegetation dynamics and the relationships with climate factors, coal mining activity and ecological restoration projects from 2000 to 2019. Results showed that vegetation in Wuhai City mostly consisted of desert plants, such as Caragana microphylla, Tetraena mongolica and Achnatherum splendens. And the vegetation fractional coverage(VFC) and greenness rate of change(GRC) showed that vegetation was slightly improved during the study period. Normalized difference vegetation index(NDVI) was positively correlated with annual mean precipitation, relative humidity and annual mean temperature, indicating that these climate factors might play important roles in the improved vegetation. Vegetation coverage and plant diversity around the coal mining area were reduced by coal mining, while the implementation of ecological restoration projects improved the vegetation coverage and plant diversity. Our results suggested that vegetation in the arid desert region was mainly affected by climate factors, and the implementation of ecological restoration projects could mitigate the impacts of coal mining on vegetation and ecological environment.     

灰色关联分析在黑岱沟露天煤矿土壤质量评价中的应用

在进行黑岱沟人工复垦地生态环境调查的基础上,对露天煤矿排土场土壤进行了理化性质、微生物及营养成分等项目的系统测试,选择了有机质、全氮、全磷、全钾、碱解氮、速效磷、速效钾、土壤水分、土壤容重、pH值、土壤3大微生物及固氮菌等项目作为评价指标,应用灰色关联度法对露天煤矿排土场土壤质量进行综合评价。结果表明:黑岱沟露天煤矿复垦区土壤质量以三等居多,四等次之,无一、二、五等;排序顺序为:各种果树(0.7209)>油松×柳×沙棘(0.7058)>锦鸡儿(0.6602)>羊草0.6165>纯杨林(人工)(0.565)≈杨林(原生)(0.556),油松林(0.5421)>杨×沙棘(0.5352)>对照(0.5154)。     

Investigating spatial and temporal variations of soil moisture content in an arid mining area using an improved thermal inertia model

Mining operations can usually lead to environmental deteriorations. Underground mining activities could cause an extensive decrease in groundwater level and thus a dramatic variation in soil moisture content(SMC). In this study, the spatial and temporal variations of SMC from 2001 to 2015 at two spatial scales(i.e., the Shendong coal mining area and the Daliuta Coal Mine) were analyzed using an improved thermal inertia model with a long-term series of Landsat TM/OLI(TM=Thematic Mapper and OLI=Operational Land Imager) data. Our results show that at large spatial scale(the Shendong coal mining area), underground mining activities had insignificant negative impacts on SMC and that at small spatial scale(the Daliuta Coal Mine), underground mining activities had significant negative impacts on SMC. Trend analysis of SMC demonstrated that areas with decreasing trend of SMC were mainly distributed in the mined area, indicating that underground mining is a primary cause for the drying trend in the mining region in this arid environment.     

Predicting of dust storm source by combining remote sensing,statistic-based predictive models and game theory in the Sistan watershed,southwestern Asia

Dust storms in arid and desert areas affect radiation budget, air quality, visibility, enzymatic activities, agricultural products and human health. Due to increased drought and land use changes in recent years, the frequency of dust storms occurrence in Iran has been increased. This study aims to identify dust source areas in the Sistan watershed (Iran-Afghanistan borders)-an important regional source for dust storms in southwestern Asia, using remote sensing (RS) and bivariate statistical models. Furthermore, this study determines the relative importance of factors controlling dust emissions using frequency ratio (FR) and weights of evidence (WOE) models and interpretability of predictive models using game theory. For this purpose, we identified 211 dust sources in the study area and generated a dust source distribution map-inventory map-by dust source potential index based on RS data. In addition, spatial maps of topographic factors affecting dust source areas including soil, lithology, slope, Normalized difference vegetation index (NDVI), geomorphology and land use were prepared. The performance of two models (WOE and FR) was evaluated using the area under curve (AUC) of the receiver operating characteristic curve. The results showed that soil, geomorphology and slope exhibited the greatest influence in the dust source areas. The 55.3% (according to FR) and 62.6% (according to WOE) of the total area were classified as high and very high potential dust sources, while both models displayed acceptable accuracy with subsurface levels of 0.704 for FR and 0.751 for WOE, although they predict different fractions of dust potential classes. Based on Shapley additive explanations (SHAP), three factors, i.e., soil, slope and NDVI have the highest impact on the model's output. Overall, combination of statistic-based predictive models (or data mining models), RS and game theory techniques can provide accurate maps of dust source areas in arid and semi-arid regions, which can be helpful for mitigation of negative effects of dust storms.     

Vegetation dynamics and its response to climate change in Central Asia

The plant ecosystems are particularly sensitive to climate change in arid and semi-arid regions. However, the responses of vegetation dynamics to climate change in Central Asia are still unclear. In this study, we used the normalized difference vegetation index(NDVI) data to analyze the spatial-temporal changes of vegetation and the correlation of vegetation and climatic variables over the period of 1982–2012 in Central Asia by using the empirical orthogonal function and least square methods. The results showed that the annual NDVI in Central Asia experienced a weak increasing trend overall during the study period. Specifically, the annual NDVI showed a significant increasing trend between1982 and 1994, and exhibited a decreasing trend since 1994. The regions where the annual NDVI decreased were mainly distributed in western Central Asia, which may be caused by the decreased precipitation. The NDVI exhibited a larger increasing trend in spring than in the other three seasons. In mountainous areas, the NDVI had a significant increasing trend at the annual and seasonal scales; further, the largest increasing trend of NDVI mainly appeared in the middle mountain belt(1,700–2,650 m asl). The annual NDVI was positively correlated with annual precipitation in Central Asia, and there was a weak negative correlation between annual NDVI and temperature. Moreover, a one-month time lag was found in the response of NDVI to temperature from June to September in Central Asia during 1982–2012.     

复垦地土壤重金属及类重金属的时间累积效应

为了揭示矿区复垦地土壤的重金属及类重金属的时间累积效应,文中以黄土高原丘陵沟壑区黑岱沟露天煤矿复垦地为研究对象,以空间代替时间的方法,在不同复垦时间的复垦地采集土壤样品,对矿区复垦地土壤的重金属及类重金属元素的时间变异性进行了研究。结果表明:复垦地土壤的重金属及类重金属元素的平均值均高于或略低于背景值,且均未超标;重金属Cu、Pb、Zn、Cd、Ni及类重金属As的累积量随着复垦时间的增加而减少(负累积效应),Hg及Cr的累积量随着复垦时间的增加而增加(正累积效应),Hg的累积效应更为明显,达到了+418.18%,Hg及Cr将成为限制复垦地再利用(农用)的主要限制因素;各种重金属及类重金属含量均处于安全等级,内梅罗指数均低于1,均处于清洁水平,内梅罗指数顺序为:PNNi>PNAs>PNCr>PNCu>PNZn>PNCd>PNHg>PNPb。     

Assessment of desertification in Eritrea: land degradation based on Landsat images

Remote sensing is an effective way in monitoring desertification dynamics in arid and semi-arid regions. In this study, we used a decision tree method based on NDVI(normalized difference vegetation index), SAVI(soil adjusted vegetation index), and vegetation cover proportion to quantify and analyze the desertification in Eritrea using Landsat data of the 1970 s, 1980 s and 2014. The results demonstrate that the NDVI value and the annual mean precipitation declined while the temperature increased over the past 40 a. Strongly desertified land increased from 4.82×10~4 km~2(38.5%) in the 1970 s to 8.38×10~4 km~2(66.9%) in 2014: approximately 85% of the land of the country was under serious desertification, which significantly occurred in arid and semi-arid lowlands of the country(eastern, northern, and western lowlands) with relatively scarce precipitation and high temperature. The non-desertified area, mostly located in the sub-humid eastern escarpment, also declined from approximately 2.1% to 0.5%. The study concludes that the desertification is a cause of serious land degradation in Eritrea and may link to climate changes, such as low and unpredictable precipitation, and prolonged drought.     

Quantitative distinction of the relative actions of climate change and human activities on vegetation evolution in the Yellow River Basin of China during 1981-2019

Under the combined influence of climate change and human activities, vegetation ecosystem has undergone profound changes. It can be seen that there are obvious differences in the evolution patterns and driving mechanisms of vegetation ecosystem in different historical periods. Therefore, it is urgent to identify and reveal the dominant factors and their contribution rates in the vegetation change cycle. Based on the data of climate elements (sunshine hours, precipitation and temperature), human activities (population intensity and GDP intensity) and other natural factors (altitude, slope and aspect), this study explored the spatial and temporal evolution patterns of vegetation NDVI in the Yellow River Basin of China from 1989 to 2019 through a residual method, a trend analysis, and a gravity center model, and quantitatively distinguished the relative actions of climate change and human activities on vegetation evolution based on Geodetector model. The results showed that the spatial distribution of vegetation NDVI in the Yellow River Basin showed a decreasing trend from southeast to northwest. During 1981-2019, the temporal variation of vegetation NDVI showed an overall increasing trend. The gravity centers of average vegetation NDVI during the study period was distributed in Zhenyuan County, Gansu Province, and the center moved northeastwards from 1981 to 2019. During 1981-2000 and 2001-2019, the proportion of vegetation restoration areas promoted by the combined action of climate change and human activities was the largest. During the study period (1981-2019), the dominant factors influencing vegetation NDVI shifted from natural factors to human activities. These results could provide decision support for the protection and restoration of vegetation ecosystem in the Yellow River Basin.     

Effects of agriculture,climate, and policy on NDVI change in a semi-arid river basin of the Chinese Loess Plateau

In 1999, the Grain for Green Project was implemented by the Chinese government. Since then, the vegetation of Zuli River Basin, a semi-arid river basin of the Chinese Loess Plateau, has been greatly changed. Clearly understanding the impact of natural and artificial factors on vegetation change is important for policy making and ecosystem management. In this study, spatio-temporal variations in vegetation cover in Chinese Zuli River Basin during 1999–2016 were investigated using Landsat normalized difference vegetation index (NDVI) data. Analyses of several indicators, including changes in NDVI in different slopes and land use changes and the relationships between climatic factors and NDVI change, were presented to quantitatively evaluate the effects of agriculture, climate, and policy on NDVI change. The NDVI in the Zuli River Basin increased during the study period, and the main contributors to this change were forest in 1999–2011, cropland, abandoned farmland, and grassland in 2009–2016, and land with slopes ≤ 15°. Land with slope > 15°, where the “Project” was implemented, slightly contributed to the increase in regional NDVI. In 1999–2011, the project (?98.16%) combined with climate change (?68.18%) showed negative effects on the increase in NDVI in the Zuli River Basin, but agriculture (22.28%) played a positive role in increasing this index. In 2009–2016 and 1999–2016, the project (38.45% and 35.25%, respectively), the project combined with climate change (49.83% and 46.30%, respectively), agriculture (18.61% and 23.30%, respectively), promoted increases in NDVI in the basin.     

陇东地区植被指数NDVI与降水的关系研究

利用1982～2003年NOAA/AVHRR(advanced very high resolution rediometer)资料及同期的降水资料,对甘肃省陇东地区半干旱区环县和半湿润区西峰的植被指数NDVI与不同时间尺度的标准化降水指数SPI进行相关分析.结果表明:在植被生长季,植被对降水的敏感程度半干旱区大于半湿润区;大多数月NDVI与3-SPI的相关系数较高,而与1-SPI较低;半干旱区和半湿润区NDVI的年变化幅度分别为:-12%～10%和-10%～13%,半干旱区NDVI的年变化与SPI变化趋势吻合较好,显著相关(P<0.05),而在半湿润区二者并不显著;半干旱区的年NDVI与四季降水均显著相关(P<0.05),而半湿润区年NDVI只与冬春季的降水显著相关(P<0.05).     

阜新市海州露天煤矿排土场植被自然恢复过程中物种多样性研究

采用野外调查和统计分析相结合的方法,对海州露天矿不同排土场物种多样性进行研究。结果表明:不同排土场,物种组成变化较大,由草本群落逐渐演变为乔木群落;物种综合多样性指数、物种丰富度指数与排土年限呈显著的正相关关系。     

Monitoring the impact of climate change andhuman activities on grassland vegetation dynamics in the northeastern Qinghai-Tibet Plateauof China during 2000-2015

Climate change and human activities can influence vegetation net primary productivity (NPP), a key component of natural ecosystems. The Qinghai-Tibet Plateau of China, in spite of its significant natural and cultural values, is one of the most susceptible regions to climate change and human disturbancesin the world. To assess the impact of climate change and human activities on vegetation dynamics in the grassland ecosystems ofthe northeastern Qinghai-Tibet Plateau, we applied a time-series trend analysis to normalized difference vegetation index (NDVI) datasets from 2000 to 2015 and compared these spatiotemporal variations with trends in climatic variables over the same time period. The constrained ordination approach (redundancy analysis) was used to determine which climatic variables or human-related factors mostly in?uenced the variation of NDVI. Furthermore, in order to determine whether current conservation measures and programs are effectivein ecological protection and reconstruction, we divided the northeastern Qinghai-Tibet Plateau into two parts: the Three-River Headwater conservation area (TRH zone) in the south and the non-conservation area (NTRH zone) in the north. The results indicatedan overall (73.32%)increasing trend of vegetation NPP in grasslands throughout the study area. During the period 2000-2015, NDVI in the TRH and NTRH zones increased at the rates of 0.0015/aand 0.0020/a, respectively.Specifically, precipitation accounted for 9.2% of the total variation in NDVI, while temperature accounted for 13.4%. In addition, variation in vegetation NPP of grasslands responded not only to long- and short-term changes in climate, as conceptualized in non-equilibrium theory, but also to the impact of human activities and their associated perturbations. The redundancy analysis successfully separated the relative contributions of climate change and human activities, of whichvillage populationand agricultural gross domestic product were the two most important contributors to the NDVI changes, explaining 17.8% and 17.1% of the total variationof NDVI (with the total contribution >30.0%), respectively. The total contributionpercentages of climate change and human activitiesto the NDVI variation were27.5% and 34.9%, respectively, inthe northeastern Qinghai-Tibet Plateau. Finally, our study shows that the grassland restoration in the study area was enhanced by protection measures and programs in the TRH zone, which explained 7.6% of the total variation in NDVI.     

Discriminating and monitoring rangeland condition classes with MODIS NDVI and EVI indices in Iranian arid and semi-arid lands

Monitoring is essential for appropriate rangeland management. The present study aimed to examine the potential of moderate resolution imaging spectroradiometer (MODIS) satellite imagery in rangeland condition assessment and monitoring within and across vegetation types in the arid and semi-arid rangelands of central Iran. The normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) were calculated from MODIS Aqua/Terra Level 1B data (related to 2003–2013). The obtained values were compared with vegetation cover measurements and rangeland condition classes at 110 sampling sites using linear regression, one-way analysis of variance (ANOVA), independent-samples t-tests, and Tukey’s pairwise comparisons. The results showed that two indices made stronger predictions of vegetation cover within a vegetation type (R²?>?0.87, P?R²?>?0.51, P?P?≤?0.001) in predicting rangeland condition classes (poor, fair, and good), but their performance varied between vegetation types. The NDVI classified about 73, 19, and 7.5% of the rangelands in poor, fair, and good condition classes, respectively. The good performance of MODIS NDVI index at different landscapes indicates that this index has high potential in detecting vegetation cover and discriminating different condition classes, therefore, it can be used to aid field- based techniques in rangeland condition assessment and monitoring.     

诺敏河流域植被覆盖时空演变及其与径流的关系研究

基于GIMMS/NDVI数据对诺敏河流域1982-2006年间植被覆盖的时空演变特征进行了研究,并结合SCS模型模拟地表径流,在流域和像元尺度分析植被NDVI变化与径流的关系。研究表明:诺敏河流域植被NDVI值较高,但25a间整体呈下降趋势,NDVI减少的区域占总面积的82.5%,植被覆盖有所降低;NDVI空间差异明显,NDVI的高值区主要分布在中上游林区,而耕地分布较多的下游地区NDVI值相对较低。流域尺度上植被NDVI与径流不具有明显的相关性。但从像元尺度来看,植被NDVI和径流的正相关和负相关共存,流域不同空间位置的植被变化与径流的关系并不一致。