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.     

Community structure and carbon and nitrogen storage of sagebrush desert under grazing exclusion in Northwest China

Overgrazing is regarded as one of the key factors of vegetation and soil degradation in the arid and semi-arid regions of Northwest China.Grazing exclusion(GE)is one of the most common pathways used to restore degraded grasslands and to improve their ecosystem services.Nevertheless,there are still significant controversies concerning GE’s effects on grassland diversity as well as carbon(C)and nitrogen(N)storage.It remains poorly understood in the arid desert regions,whilst being essential for the sustainable use of grassland resources.To assess the effects of GE on community characteristics and C and N storage of desert plant community in the arid desert regions,we investigated the community structure and plant biomass,as well as C and N storage of plants and soil(0-100 cm depth)in short-term GE(three years)plots and adjacent long-term freely grazing(FG)plots in the areas of sagebrush desert in Northwest China,which are important both for spring-autumn seasonal pasture and for ecological conservation.Our findings indicated that GE was beneficial to the average height,coverage and aboveground biomass(including stems,leaves and inflorescences,and litter)of desert plant community,to the species richness and importance values of subshrubs and perennial herbs,and to the biomass C and N storage of aboveground parts(P<0.05).However,GE was not beneficial to the importance values of annual herbs,root/shoot ratio and total N concentration in the 0-5 and 5-10 cm soil layers(P<0.05).Additionally,the plant density,belowground biomass,and soil organic C concentration and C storage in the 0-100 cm soil layer could not be significantly changed by short-term GE(three years).The results suggest that,although GE was not beneficial for C sequestration in the sagebrush desert ecosystem,it is an effective strategy for improving productivity,diversity,and C and N storage of plants.As a result,GE can be used to rehabilitate degraded grasslands in the arid desert regions of Northwest China.     

Influence of edaphic factors on plant distribution and diversity in the arid area of Xinjiang,Northwest China

The influence of edaphic factors on plant distribution is essential to community ecology and important for vegetation restoration and management in arid ecosystems. In this study, desert plant distribution and diversity as well as soil water, salinity, and nutrients were measured in the Ebinur Lake Wetland Nature Reserve (ELWNR) in arid Northwest China. We determined relationships between plant distribution and soil factors along a transect with increasing distance from the river and created optimal models using soil factors to explain variations in plant diversity. In general, soil factors decreased with increasing distance from the river. Soil volumetric water content (SVWC), electrical conductivity (EC), pH, nitrogen (N), phosphorus (P), and sulfur (S) were closely related to plant distribution. According to canonical correspondence analysis, plants along the transect were divided into three groups: saline–alkaline tolerant, drought tolerant, and high P-demanding. SVWC, pH, soil organic carbon (C), N, P, and S account for 93.8% of the variations in plant diversity in the ELWNR. Compared with other soil factors, S explained the largest percentage of variations in diversity when single soil variables were considered in generalized additive models (R²?=?38.9%). Our results suggest increases in soil pH, P, N, and S would improve plant diversity significantly. We found differences among species groups in preference for habitat, and N and S content had a significant positive effect of on plant diversity, providing a scientific reference for plant restoration and saline soil remediation in desert ecosystems.     

荒漠植物红砂(Reaumuria soongorica)的保育效应及其对群落物种多样性的影响

红砂(Reaumuria soongorica)是我国北方温带荒漠的主要先锋植物,也是一种潜力巨大的水土保持和荒山绿化物种,但是该乡土物种是否具有保育植物的特征,目前尚未有这方面的研究。文中通过研究生长于半干旱区的荒漠植物红砂群落不同分布格局和群落特征,分析红砂盖度变化对群落多样性的影响,探究保育效应的发生条件及其对群落物种多样性影响机理。研究结果表明:群落的植物物种多样性随着红砂植被盖度和地上生物量增大而逐渐增大,然而,当红砂总盖度超过48.73%(地上生物量为35.62g/m2)时,虽植被盖度和地上生物量继续增大,目标物种碱蓬(Suaeda glauca),蓍状亚菊(Ajania achilleoides)多度明显增加,但植物物种多样性并没有显著的变化。这些说明在干旱区,当红砂的盖度增加到一定程度之后,才能通过冠层遮阴产生保育效应。因此,在植被稀疏、物种多样性较低的干旱地区,可以充分利用红砂物种的保育效应,促进和加快植被自然恢复进程,调控物种多样性和群落结构。     

荒漠草地物种多样性的水分特征研究

通过在伊犁河谷山前倾斜平原荒漠草地开展的不同灌溉量草地恢复试验,对测试的试验地内草地植物物种多样性指数和灌溉水量之间的关系进行了初步的研究。结果显示:在荒漠草地,水分是影响草地植物长势的重要限制因子,随着水分条件的转好,植被盖度和蒿类的分盖度均有显著的提高,草地植物的生物量和群丛高度均显著增加;随着灌溉量的增加,S im pson指数、Shannon-W iener指数、P ie lou指数和M arga lef指数均出现递增的趋势,其中每增加1 kg/d水量,S im pson指数将增加0.021,表明在温性荒漠草原生物多样性指数对水量变化的灵敏度较高。     

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.     

Seasonal differences in climatic controls of vegetation growth in the Beijing-Tianjin Sand Source Region of China

Launched in 2002, the Beiing-Tianjin Sand Source Control Project (BTSSCP) is an ecological restoration project intended to prevent desertification in China. Evidence from multiple sources has confirmed increases in vegetation growth in the BTSSCP region since the initiation of this project. Precipitation and essential climate variable-soil moisture (ECV-SM) conditions are typically considered to be the main drivers of vegetation growth in this region. Although many studies have investigated the inter-annual variations of vegetation growth, few concerns have been focused on the annual and seasonal variations of vegetation growth and their climatic drivers, which are crucial for understanding the relationships among the climate, vegetation, and human activities at the regional scale. Based on the normalized difference vegetation index (NDVI) derived from MODIS and the corresponding climatic data, we explored the responses of vegetation growth to climatic factors at annual and seasonal scales in the BTSSCP region during the period 2000-2014. Over the study region as a whole, NDVI generally increased from 2000 to 2014, at a rate of 0.002/a. Vegetation growth is stimulated mainly by the elevated temperature in spring, whereas precipitation is the leading driver of summer greening. In autumn, positive effects of both temperature and precipitation on vegetation growth were observed. The warming in spring promotes vegetation growth but reduces ECV-SM. Summer greening has a strong cooling effect on land surface temperature. These results indicate that the ecological and environmental consequences of ecological restoration projects should be comprehensively evaluated.     

Attribution analysis based on Budyko hypothesis for land evapotranspiration change in the Loess Plateau,China

Land evapotranspiration (ET) is an important process connecting soil, vegetation and the atmosphere, especially in regions that experience shortage in precipitation. Since 1999, the implementation of a large-scale vegetation restoration project has significantly improved the ecological environment of the Loess Plateau in China. However, the quantitative assessment of the contribution of vegetation restoration projects to long-term ET is still in its infancy. In this study, we investigated changes in land ET and associated driving factors from 1982to 2014 in the Loess Plateau using Budyko-based partial differential methods. Overall, annual ET slightly increased by 0.28 mm/a and there were no large fluctuations after project implementation. An attribution analysis showed that precipitation was the driving factor of inter-annual variability of land ET throughout the study period; the average impacts of precipitation, potential evapotranspiration, and vegetation restoration on ET change were 61.5%, 11.5% and 26.9%, respectively. These results provide an improved understanding of the relationship between vegetation condition change and climate variation on terrestrial ET in the study area and can support future decision-making regarding water resource availability.     

民勤荒漠植被的形成与演替过程及其发展趋势

甘肃省民勤县是我国的典型荒漠化地区,自西汉以来生态环境逐渐退化,植被经历了一个从沼泽植被到盐生草甸植被再到荒漠植被的退化过程。水资源的变化是决定当地植被退化的主导因子,在大面积湖泊、河流背景上是沼泽植被,在干涸湖泊、河床背景上的是盐生草甸植被,在沙质荒漠背景上的是荒漠植被。目前,荒漠植被正处于进一步退化过程中。退化演替的同一阶段存在多种演替过程,现阶段存在着荒漠植被退化演替和盐生草甸植被向荒漠植被演替2种退化过程。20世纪中叶,在当地是从盐生草甸植被向荒漠植被演替的过渡时期,20世纪50年代以来,荒漠植被逐渐占据了优势。目前的天然种子植物共有22个科,72个属,127个种,其中以典型荒漠为主,共有3个植被型,7个群系组,17个群系。植物种类少,群落结构简单,群落随生境的分异性较大。目前的植被正处在进一步退化过程中,植物种类和面积减少,大面积枯梢、死亡,优势种的优势度增大。现阶段决定荒漠植被生长状况的主要是大气降水,植被盖度和密度随年际降水量变化较大,尤其是一年生草本植物。目前影响植被退化的人为因素主要是上游来水量减少,地下水严重超采、草场严重超载和造林密度过大等。在干旱内陆盆地,一旦水资源供给减少,湖盆、河道干涸,泥沙出露,形成沙漠和沙漠化则是必然结果。     

民勤沙区主要植物群落退化特征及其演替趋势分析

优势种植物密度和优势种盖度以及全部植物密度和盖度在样方间均存在不同程度的差异,表明民勤的植物生长在受干旱荒漠环境影响的同时,局部小环境对植物的分布和生长有显著影响。沙蒿当年幼苗密度最大,但幼苗的成活率很低,群落的投影盖度越小,则当年幼苗密度越大;梭梭不能实现自然更新;沙拐枣的生态位宽度较大,各年龄小苗均存在,自然更新能力强。在民勤沙区人工梭梭林普遍退化,尤其在西沙窝一带,梭梭人工林退化更为严重,有被沙拐枣取代的趋势。由于梭梭群落均为人工林,群落内地表异质性较大,因此,草本植物种类较多。     

草方格沙障的生态恢复作用——以古尔班通古特沙漠油田公路扰动带为例

统计描述阜彩路、准东沙漠油田公路两条古尔班通古特沙漠内的油田公路扰动带内植物样方和采集不同年龄草方格内表层，次表层及草方格外的表层沙样，在室内实验分析，比较沙样粒度配比，有机质和盐分含量，初步总结出了草方格沙障对公路扰动带的生态恢复作用；降低近地表风速，草方格内积沙，表层细粒沙物质含量增加，形成稳定的沙面环境，使植物种子易于着床、生长、沙表层的有机质、盐分含量随着时间而增加，促进了生物结皮的发育。     

乌兰布和东北部荒漠-绿洲生态交错带植被特征及其群落多样性研究

以2009年9月乌兰布和沙区植物群落样方调查资料为基础,对其农牧交错带内不同生境的植被特征及其物种多样性进行研究。结果表明：在区域干旱气候的共同背景下,由于受人工绿洲灌溉水分水平运动影响的强度不同,导致该生态交错带内山前洪积扇、人工绿洲周边、绿洲外围植被的组成及其群落多样性差异显著,水平空间尺度上群落变异性大,构成群落...     

陇东北部土壤沙化现状及防治对策

采用定点观测及调查等方法对沙区土壤沙化的现状及成因进行了分析研究。结果表明:沙区有沙漠化土地210 496 hm2,占沙区总面积(540 950 hm2)的38.91%,沙漠化平均每年沙线从西北向东推进0.54 km。特定的地质构造和毛乌素沙地为沙化提供了物质条件及外部来源,干旱多风、风蚀水侵等自然灾害和资源的不合理利用对当地农业造成了严重危害。防治土壤沙化的对策:治沙先种草,草灌结合;建立草—灌—乔“山型”体系和林、草、田复合生态系统,控制沙线南移;在荒芜的沙地大量种植耐牧的灌木,沙打旺等牧草;加大宣传力度,提高沙区人民的防沙、治沙意识;通过人大立法,迅速制止无限度的垦荒;放宽政策,鼓励退耕还林还草、退牧还草,促进沙区经济的可持续发展。     

Effects of climate change on phenology and primary productivity in the desert steppe of Inner Mongolia

 Variations in temperature and precipitation affect local ecosystems. Considerable spatial and temporal heterogeneity exists in arid ecosystems such as desert steppes. We analyzed the spatiotemporal dynamics of climate and vegetation phenology in the desert steppe of Inner Mongolia, China, using meteorological data from 11 stations (1961–2010) and phenology data from 6 ecological stations (2004–2012). We also estimated the gross primary production for the period of 1982–2009 and found that the annual mean temperature increased at a rate of 0.47ºC/decade during 1961–2010, with the last 10 years being consistently warmer than the 50-year mean. The most significant warming occurred in winters. Annual precipitation slightly decreased during the 50-year period, with summer precipitation experiencing the highest drop in the last 10 years, and spring precipitation, a rise. Spatially, annual precipitation increased significantly in the northeast and eastern central area of the region next to the typical steppe. From 2004 to 2012, vegetation green-up and senescence date advanced in the area, shortening the growing season. Consequently, the primary productivity of the desert steppe decreased along precipitation gradient from southeast to northwest. Temporally, productivity increased during the period of 1982–1999 and significantly decreased after 2000. Overall, the last decade witnessed the most dramatic climatic changes that were likely to negatively affect the desert steppe ecosystem. The decreased primary productivity, in particular, decreases ecosystem resilience and impairs the livelihood of local farmers and herdsmen.     

中麻黄的适应性及其抗逆性栽培

中麻黄具有较强的旱生性和耐盐性 ,在逆境盐碱地栽培其经济效益、缓解天然麻黄资源破坏、减缓土地沙化的生态效益比较显著 ,是干旱区盐碱地农村调整种植结构、退耕还林的优良植物种。     

Plant community dynamics in arid lands: the role of desert ants

Ants (Formicidae, Hymenoptera) play an important role in seed bank, seedling establishment andplant composition of arid ecosystems. Thus, knowing plant-ant interaction provides useful information formanagers to design restoration and conservation plans. In this study, the roles of desert harvester ants (Messorintermedius and Messor melancholicus) and scavenger ants (Cataglyphis nodus and Lepisiota semenovi) on plantcommunities were investigated in arid ecosystems of southeastern Iran. Two vegetation types weredistinguished in the study area and the nest density of ant species was determined. Furthermore, plantcomposition and soil seed bank were estimated at different distances from the ant nests. Results showed thatthe density of M. intermedius and M. melancholicus nests was higher in dwarf shrub-shrub vegetation type and thedensity of C. nodus and L. semenovi nests was higher in dwarf shrub vegetation type. The harvester and scavengerants had enhanced the seed bank to 55% and 70%, respectively. Therefore, the role of scavenger ants on theplant communities' seed bank was greater than that of harvester ants. Although the scavenger ants were moreinfluential on the annuals and the invasive plant species, the radius impact of the harvester ants on theperennials was greater, i.e., a positive interaction existed between the perennial plants and the harvester ants. C.nodus and L. semenovi played an important role in enhancing the ecosystem's potential for restoration throughestablishment of pioneer species in early stage of succession. The activity of M. intermedius is crucial for thedevelopment and maintenance of climax plant communities in arid ecosystems through assisting the plantspecies' establishment in late stage of succession. It is essential to preserve the diversity of these key ant speciesfor the maintenance and sustainability of shrubs in arid ecosystems.     

Spatial variability of soil water content and related factors across the Hexi Corridor of China

Soil water content(SWC) is a key factor limiting ecosystem sustainability in arid and semi-arid areas of the Hexi Corridor of China, which is characterized by an ecological environment that is vulnerable to climate change. However, there is a knowledge gap regarding the large-scale spatial distribution of SWC in this region. The specific objectives of this study were to determine the spatial distribution patterns of SWC across the Hexi Corridor and identify the factors responsible for spatial variation of SWC at a regional scale. This study collected and analyzed SWC in the 0–100 cm soil profile from 109 field sampling sites(farmland, grassland and forestland) across the Hexi Corridor in 2017. We selected 17 factors, including land use, topography(latitude, longitude, elevation, slope gradient, and slope aspect), soil properties(soil clay content, soil silt content, soil bulk density, saturated hydraulic conductivity, field capacity, and soil organic carbon content), climate factors(mean annual precipitation, potential evaporation, and aridity index), plant characteristic(vegetation coverage) and planting pattern(irrigation or rain-fed), as possible environmental variables to analyze their effects on SWC. The results showed that SWC was 0.083(±0.067) g/g in the 0–100 cm soil profile and decreased in the order of farmland, grassland and forestland. The SWC in the upper soil layers(0–20, 20–40 and 40–60 cm) had obvious difference when the mean annual precipitation differed by 200 mm. The SWC decreased from southeast to northwest following the same pattern as precipitation, and had a moderate to strong spatial dependence in a large effective range(75–378 km). The SWC showed a similar distribution and had no significant difference between soil layers in the 0–100 cm soil profile. The principal component analysis showed that the mean annual precipitation, geographical position(longitude and latitude) and soil properties(soil bulk density and soil clay content) were the main factors dominating the variance of environmental variables. A stepwise linear regression equation showed that plant characteristic(vegetation coverage) and soil properties(soil organic carbon content, field capacity and soil clay content) were the optimal factors to predict the variation of SWC. Soil clay content could be better to explain the SWC variation in the deeper soil layers compared with the other factors.     

干旱区荒漠景观植被自然更新机制初探

根据实地调查和参阅资料,依山前洪积扇、河流沿岸阶地、沙丘及丘间低地、戈壁、盐沼的景观斑块,探讨干旱区荒漠植被的自然更新机制。干旱区的高温干燥、温差强烈、风蚀沙埋已变为植物繁衍后代的动力;萌孽、劈裂、地下茎萌生等多种繁殖方式,使荒漠植物在严酷的条件下实现自然更新,形成以母株为中心的母系居群。地貌形态和种子传播动力决定了群落外形。在干旱区,繁殖植物的种子成熟期与年内的丰水期相吻合,有利于植被更新：只有在连续2a降水较大时（超过多年平均降水量）,沙丘和丘间地、戈壁植被的自然更新才有可能发生。河流沿岸植被的自然更新受地下水影响最明显。湖盆盐碱地植被带有水生植被的痕迹,自然更新相对较难。景观斑块镶嵌分布,形成微环境均一的廊道,有利于植被的自然更新。     

玛纳斯河流域生态环境质量时空分异评价

利用3S空间分析和地学统计分析方法,选取植被覆盖度、坡度、土壤等归一化生态指数,采用生态要素及功能叠加的转移矩阵模型,研究了新疆玛纳斯河流域生态要素及环境质量时空分异规律。研究得出:①总体上玛纳斯河流域仍保持山地、绿洲、荒漠的空间分异格局,生态环境整体质量较差,但转好趋势明显,城乡建设格局变化决定着局地环境动态演变。②人工绿洲、山前缓冲区生态质量最好但变化较快,农田内部的盐渍化虽然得到很好控制,但大量盐分被排入下游及周边,对自然绿洲造成新的危害。中山林草带植被覆盖、土壤恢复、水土保持较好。③2000-2008年流域生态环境质量缓慢好转,其中以生态环境质量由差转中为主,集中在古尔班通古特沙漠,虽然绿洲-荒漠过渡带生态恢复明显,但高山冰雪带不断萎缩;2008-2016年流域生态环境质量明显转好,其中以生态环境质量由中变良为主,集中在山前缓冲区,虽然山地-绿洲过渡带生态改善进程加快,但高山冰雪带仍持续退缩。     

鄂尔多斯高原西部阿拉巴斯山地区第三纪残遗植物避难所的自然保护问题

阿拉巴斯山地区为干旱区第三纪残遗植物的避难所,是内蒙古地区植物特有现象最明显的地区。共有维管植物251种。地带性植被为草原化荒漠,主要群落类型为四合木荒漠、半日花荒漠、绵刺荒漠、沙冬青荒漠等荒漠群系。以戈壁种和东阿拉善种为主的荒漠成分构成了本地区植物区系的主体。古老残遗种及特有种在植物区系和植被组成中均起主导作用。但是这块宝地目前面临严重破坏,应该尽快成立阿拉巴斯第三纪残遗植物保护区。