Assessing the impact of ecological and economic factors on land degradation vulnerability through multiway analysis

Land degradation (LD) is a global problem which involves climate, soil, vegetation, economic, and population conditions. In Mediterranean Europe climatic variability and human pressure combine to produce soil sealing, erosion, salinisation, fire risk, and landscape fragmentation, all regarded as important factors to start LD. The aim of this paper is to introduce a time-series evaluation of land vulnerability to degradation based on nine ecological and economic variables. The analysis was carried out over 1970–2000 at the municipality level in Latium (central Italy), a region which has shown increasing land vulnerability in the last years. A multiway data analysis (MDA) was applied in order to explore the relationship among indicators over the study period. Their importance in determining LD vulnerability was estimated through a weighting system based on MDA results. A composite index of land vulnerability (LVI) was obtained as the weighted average of the nine variables transformed into single indicators, according to their relationship with LD. Considerable increases in LVI were observed in dry coastal and lowland municipalities close to Rome, thus indicating that climate aridity, population growth, and land use changes are important determinants of land vulnerability in Latium. LVI was positively correlated to the environmental sensitive area index (ESAI) measured on the same spatial and time scales, thus suggesting that a sound evaluation of land vulnerability is possible through LVI score.     

Water and energy footprints of bioenergy crop production on marginal lands

Water and energy demands associated with bioenergy crop production on marginal lands are inextricably linked with land quality and land use history. To illustrate the effect of land marginality on bioenergy crop yield and associated water and energy footprints, we analyzed seven large‐scale sites (9–21 ha) converted from either Conservation Reserve Program (CRP) or conventional agricultural land use to no‐till soybean for biofuel production. Unmanaged CRP grassland at the same location was used as a reference site. Sites were rated using a land marginality index (LMI) based on land capability classes, slope, soil erodibility, soil hydraulic conductivity, and soil tolerance factors extracted from a soil survey (SSURGO) database. Principal components analysis was used to develop a soil quality index (SQI) for the study sites based on 12 soil physical and chemical properties. The water and energy footprints on these sites were estimated using eddy‐covariance flux techniques. Aboveground net primary productivity was inversely related to LMI and positively related to SQI. Water and energy footprints increased with LMI and decreased with SQI. The water footprints for grain, biomass and energy production were higher on lands converted from agricultural land use compared with those converted from the CRP land. The sites which were previously in the CRP had higher SQI than those under agricultural land use, showing that land management affects water footprints through soil quality effects. The analysis of biophysical characteristics of the sites in relation to water and energy use suggests that crops and management systems similar to CRP grasslands may provide a potential strategy to grow biofuels that would minimize environmental degradation while improving the productivity of marginal lands.     

Towards a process-based evaluation of land vulnerability to soil degradation in Italy

This paper illustrates a process-based approach aimed at classifying large areas into different classes of vulnerability to Mediterranean land and soil degradation (LD and SD). A wide set of environmental and socio-economic variables was used to describe five soil degradation processes (soil erosion, salinisation, sealing, contamination, and compaction) and climate taken together as the final determinants of LD in Italy. The elementary variables contributed to generate six thematic indicators which depict the level of vulnerability of the country to each degradation process. The Multivariate Soil Degradation Vulnerability Index (MSDVI) provided an estimation of the level of land vulnerability by aggregating the six indicators. Multidimensional analyses and Geographic Information System tools were used to derive the thematic indicators and the synthetic index. Results demonstrated that in Italy, climate, soil erosion, and soil compaction/agricultural intensification represent the soil degradation processes with a potentially higher role in determining vulnerability to LD, even if with different spatial configuration patterns. On average, the most vulnerable area was insular Italy, followed by southern Italy; northern and central Italy were found less vulnerable to LD, however the MSDVI was found locally high also in northern Italy. The validation tests performed on MSDVI by field assessment and comparison with ancillary data indicated that the index is a reliable proxy of land vulnerability to soil degradation. Advantages of this approach compared to other procedures aimed at assessing LD were finally discussed.     

围栏对青藏高原不同类型草地土壤原核微生物多样性的影响

草地退化是草地植被的倒退演替,导致生物多样性丧失和生态系统功能退化,围栏是恢复退化草地生态系统功能的有效管理措施。微生物是土壤中的重要组成部分,在维持草地生态系统稳定性和功能方面发挥着重要作用。然而,目前尚不清楚围栏如何影响不同类型草地土壤微生物群落。以青藏高原草甸、草原和荒漠草地三种草地类型的退化草地为研究对象,设置围栏和放牧两种处理,采用Illumina HiSeq高通量测序技术研究了围栏对土壤原核微生物群落多样性和群落结构的影响。结果表明：围栏未显著影响草甸土壤原核微生物的丰富度、Shannon多样性和均匀度,但显著增加了草原土壤的原核微生物的丰富度、Shannon多样性和均匀度（P<0.05）,稍降低了荒漠草地土壤原核微生物的丰富度、Shannon多样性和均匀度（P=0.086、0.072和0.099）。在围栏处理的草地中,土壤原核微生物丰富度、Shannon多样性和均匀度与年均温、干旱度和pH显著负相关（P<0.01）,与年平均降水量、溶解性有机碳、地上生物量和植物多样性显著正相关（P<0.01）。在放牧处理的草地中,土壤原核微生物丰富度、Shannon多样性和均匀度与年均温和干旱度显著负相关（P<0.05）,但原核微生物丰富度和Shannon多样性与所有土壤理化和植被因素均无显著相关性。冗余分析（RDA）表明,不同类型草地土壤原核微生物群落结构发生了显著的变化,并沿草甸、草原和荒漠草地的过渡逐渐转变（P<0.001）。方差分解分析（VPA）进一步表明,原核微生物群落结构变化主要受年均温、年平均降水量、干旱度和pH的驱动。围栏显著改变了不同类型草地中部分样点土壤原核微生物群落结构。三种草地类型的主要原核微生物优势门均为放线菌门（Actinobacteria）、变形菌门（Proteobacteria）和酸杆菌门（Acidobacteria）。放线菌门（Actinobacteria）的相对丰度在荒漠草地土壤中最高,而变形菌门（Proteobacteria）和酸杆菌门（Acidobacteria）的相对丰度在草甸土壤中最高。此外,不同类型围栏和放牧草地土壤原核微生物类群的相对丰度均无显著差异。研究表明不同类型草地土壤原核微生物群落对围栏的响应不同,这为因地制宜制定草地管理措施提供了数据支持,为草地退化的防治提供了理论支持。     

黄土高原归一化植被指数与自然环境因子的空间关联性——基于地理探测器

植被对改善黄土高原脆弱的生态环境有着关键作用,系统研究黄土高原归一化植被指数(NDVI)空间分布和环境因子的空间关联性,可为新时代黄土高原植被高质量建设提供科学依据。以黄土高原2000-2017年年均植被NDVI为研究对象,选取气候要素、地形因素、土壤类型和植被类型等自然环境因子,运用GIS和地理探测器技术手段,在剔除土地利用类型发生变化栅格的基础上,研究黄土高原年均NDVI与环境因子的空间关联性,结果表明:2000-2017年黄土高原年均NDVI值在0.016-0.72之间,呈地带性分布,由西北部向东南部逐渐升高,大于0.3的区域占50.23%;2000-2017年黄土高原年均植被NDVI分布具有空间异质性,且在不同植被区、地貌区、土壤区和气候区中,NDVI空间分布的主要环境驱动因子具有差异性。年均降雨量对NDVI空间分布具有强解释力,是黄土高原85.20%的区域植被生长的主要制约因子;约12.01%的区域主要受土壤类型影响,为中等解释力,其余区域的植被生长主要受年均气温,日照时数或海拔影响。建议综合考虑不同环境条件下植被NDVI的空间分布与环境影响因子的空间关联性,明确不同区域中植被NDVI的环境制约因子,以制约因子定植,在防止土壤干燥化、贫瘠化的前提下,提高植被覆盖率和生物多样性,以期促进黄土高原植被建设高质量发展。     

黄土高原小流域不同地形下土壤有机碳分布特征

研究了黄土高原小流域尺度塬面、坡地、沟道和梯田4种地形条件下土壤有机碳总量和活性组分的分布、储量及碳库管理指数的差异.结果表明,小流域土壤有机碳和不同活性有机碳的变异系数介于32％-70％之间,表现出中到高度的变异特征.4种地形下各组分有机碳含量和储量以塬面土壤最高,沟道土壤最低,并随土层深度的增加而降低,降低程度随有机碳活性增强而增加.以塬面土壤为对照所获得的碳库管理指数可灵敏指示有机碳对地形条件的响应特征,中活性有机碳库管理指数的指示效果最好.研究结果可部分解释黄土高原土壤有机碳地带性分布特征.     

南方水土流失严重区的生态脆弱性时空演变

生态环境脆弱性评价研究,对生态环境保护与修复具有重要意义.以福建省长汀县为研究区,选择坡度、土壤类型、多年平均降雨量、地形起伏度、归一化植被指数、人口密度、土地利用类型7个指标,通过多重共线性诊断分析,构建生态脆弱性评价指标体系,采用熵权法及综合指数法对1999、2006和2014年长汀县生态脆弱性进行定量评价,分析生态脆弱性时空分布及变化.结果表明: 1999—2014年,研究区生态脆弱性等级指数总体减小,局部增大.研究区1999、2006和2014年生态脆弱性指数平均值分别为0.4533±0.1216、0.4160±0.1110和0.3916±0.1139,整体处于中等脆弱水平;生态脆弱性等级指数从1999年的2.92下降到2006年的2.38,再下降到2014年的2.13.生态脆弱性的空间格局呈内高外低的分布特征,高脆弱等级区主要分布在坡度<15°、海拔<500 m的河田镇及汀州镇一带.研究期间,生态脆弱性等级指数降幅最大的是三洲乡,最小的是汀州镇.     

西北干旱区生态脆弱性时空演变分析

西部大开发政策实施以来,随着社会经济的发展和环境政策的调整,西北干旱区生态环境发生深刻变化。基于西北干旱区生态本底特征,选取土壤、地形、气候并结合夜间灯光数据构建西北干旱区生态脆弱性评价体系,运用空间主成分分析法（SPCA）、地理探测器对西北干旱区2000、2007、2012、2018年生态脆弱性时空演变及驱动力进行分析。结果表明：（1）从西北干旱区生态脆弱性时空演变特征来看,研究区生态脆弱性以重度脆弱性为主;从不同土地利用脆弱性来看,微度脆弱区以草地、林地为主,轻度脆弱区以草地为主,中度脆弱区和重度脆弱区以未利用地为主,18年来研究区生态脆弱性整体保持不变;（2）影响西北干旱区生态脆弱性分异的主导因素包括土壤有机质含量、地形位指数、气温、降水、夜间灯光指数,各因素对生态脆弱性的平均决定力分别为0.63、0.36、0.27、0.26和0.22。（3）基于生态脆弱性监测结果和驱动因素分析,将西北干旱区划分为5个生态功能区：生态核心保护区、生态综合监测区、生态优化关注区、生态恢复治理区、生态潜在治理区,并提出相应管理方案。研究可以为干旱区生态环境保护提供借鉴。     

Effects of climate on soil phosphorus cycle and availability in natural terrestrial ecosystems

Climate is predicted to change over the 21st century. However, little is known about how climate change can affect soil phosphorus (P) cycle and availability in global terrestrial ecosystems, where P is a key limiting nutrient. With a global database of Hedley P fractions and key‐associated physiochemical properties of 760 (seminatural) natural soils compiled from 96 published studies, this study evaluated how climate pattern affected soil P cycle and availability in global terrestrial ecosystems. Overall, soil available P, indexed by Hedley labile inorganic P fraction, significantly decreased with increasing mean annual temperature (MAT) and precipitation (MAP). Hypothesis‐oriented path model analysis suggests that MAT negatively affected soil available P mainly by decreasing soil organic P and primary mineral P and increasing soil sand content. MAP negatively affected soil available P both directly and indirectly through decreasing soil primary mineral P; however, these negative effects were offset by the positive effects of MAP on soil organic P and fine soil particles, resulting in a relatively minor total MAP effect on soil available P. As aridity degree was mainly determined by MAP, aridity also had a relatively minor total effect on soil available P. These global patterns generally hold true irrespective of soil depth (≤10 cm or >10 cm) or site aridity index (≤1.0 or >1.0), and were also true for the low‐sand (≤50%) soils. In contrast, available P of the high‐sand (>50%) soils was positively affected by MAT and aridity and negatively affected by MAP. Our results suggest that temperature and precipitation have contrasting effects on soil P availability and can interact with soil particle size to control soil P availability.     

Agro-ecological field vulnerability evaluation and climate change impacts in Souma area (Iran), using MicroLEIS DSS

Soil erosion and contamination are two main desertification indices or land degradation agents in agricultural areas. Global climate change consequence is a priority to predict global environmental change impacts on these degradation risks. This agro-ecological approach can be especially useful when formulating soil specific agricultural practices based on the spatial variability of soils and related resources to reverse environmental degradation. Raizal and Pantanal models within the new MicroLEIS framework, the Ero&Con package, are database/expert system evaluation approach for assessing limitations to land use, or vulnerability of the land to specified agricultural degradation risks. This study was performed in Souma area with approximately 4100 ha extension in the North-West of Iran (west Azarbaijan). Based on 35 sampling soils, Typic Xerofluvents, Typic Calcixerepts, Fluventic Haploxerepts and Fluventic Endaquepts were classified as main subgroups. Climatological data, referred to temperature and precipitation of more than 36 consecutive years were collected from Urmieh station reports and stored in monthly Climate Database CDBm, as a major component of MicroLEIS DSS (CDBm) program. Climate data for a hypothetical future scenario were collected from the Intergovernmental Panel on Climate Change (IPCC) reports for the 2080s period. The evaluation approach predicts that attainable water erosion vulnerability classes were none (V1) very low (V2) and moderately low (V4) in the total of 72%, 13% and 15% of the Souma area, respectively and they will not affected by climate change. On contrary, attainable wind erosion vulnerability classes will increase. Also, phosphorous and heavy metal contamination vulnerability risks will not differ in two compared scenarios while nitrogen and pesticides vulnerability classes will be improved.     

Comparison of Soil Quality Index Using Three Methods

Assessment of management-induced changes in soil quality is important to sustaining high crop yield. A large diversity of cultivated soils necessitate identification development of an appropriate soil quality index (SQI) based on relative soil properties and crop yield. Whereas numerous attempts have been made to estimate SQI for major soils across the World, there is no standard method established and thus, a strong need exists for developing a user-friendly and credible SQI through comparison of various available methods. Therefore, the objective of this article is to compare three widely used methods to estimate SQI using the data collected from 72 soil samples from three on-farm study sites in Ohio. Additionally, challenge lies in establishing a correlation between crop yield versus SQI calculated either depth wise or in combination of soil layers as standard methodology is not yet available and was not given much attention to date. Predominant soils of the study included one organic (Mc), and two mineral (CrB, Ko) soils. Three methods used to estimate SQI were: (i) simple additive SQI (SQI-1), (ii) weighted additive SQI (SQI-2), and (iii) statistically modeled SQI (SQI-3) based on principal component analysis (PCA). The SQI varied between treatments and soil types and ranged between 0–0.9 (1 being the maximum SQI). In general, SQIs did not significantly differ at depths under any method suggesting that soil quality did not significantly differ for different depths at the studied sites. Additionally, data indicate that SQI-3 was most strongly correlated with crop yield, the correlation coefficient ranged between 0.74–0.78. All three SQIs were significantly correlated (r = 0.92–0.97) to each other and with crop yield (r = 0.65–0.79). Separate analyses by crop variety revealed that correlation was low indicating that some key aspects of soil quality related to crop response are important requirements for estimating SQI.     

闽三角城市群生态环境脆弱性及其驱动力

生态安全是地区社会经济可持续发展的基本前提之一,而生态环境脆弱性会威胁地区的生态安全,进行生态环境脆弱性评价具有重要意义。以闽三角城市群为例,分别选取2000年和2015年的高程、坡度、岩性、土壤类型、NDVI、年均降水量、年均温、人口密度、人均GDP、路网密度、景观多样性、土地利用程度和工业固体废弃物排放量等13个指标,基于空间主成分分析法,并结合全局Moran'I和LISA聚类图,从整体特征、空间差异、空间集聚、地类脆弱性分异以及驱动力5个方面,探讨闽三角城市群的生态环境脆弱性及其驱动力。结果表明:2000—2015年间,闽三角城市群的生态环境脆弱性整体处于中度脆弱,但呈现出由中度脆弱向重度脆弱过渡的趋势;2000—2015年间,生态环境脆弱性呈现出由东南沿海向西北内陆逐渐增强的整体趋势,并存在明显的地带性特征,东南沿海增长不明显,部分地区有所下降,而西北内陆增长明显;生态环境脆弱性存在显著的空间自相关性,且为显著正相关,在西北部山区地带为显著的高高聚集,在东南沿海平原地带为显著的低低聚集,16年间集聚性特征在空间上有所迁移和扩张;2000—2015年间,生态环境脆弱性在各地类存在着一定的异质性,其生态环境脆弱性指数大小顺序始终为:林地未利用地草地耕地水域建设用地,整体由中度脆弱向重度脆弱过渡;2000—2015年间,生态环境脆弱性的驱动力有所变化,但人口密度、景观多样性、岩性和土壤类型一直是闽三角城市群生态环境脆弱性主要的驱动力。     

植被恢复对西南喀斯特地区土壤气候韧性的提升作用

土壤质量提升是生态系统应对气候变化能力增强的关键。为探究气候变化背景下不同植被恢复方式对喀斯特地区土壤质量的影响,基于黔桂喀斯特地区气候梯度样带84个样方土壤物理、化学和生物性质综合分析,分别以耕地和次生林作为退化和顶级恢复对照,探讨了自然恢复(灌木林)和人工恢复(人工林)的土壤质量提升效应及其对气候变化的响应。结果表明:(1)植被恢复不仅显著提高了土壤细菌、真菌、放线菌等微生物丰度以及有机碳、全氮、速效氮等养分含量,也对土壤质地有一定改善;(2)自然恢复和人工恢复均提高了土壤质量,两种恢复方式之间土壤质量指数无显著差异,但与次生林依然存在差距。灌木林和人工林的土壤质量仅约为次生林土壤质量的62%-66%;(3)耕地土壤质量随年均温和年平均降雨量的增加而下降,次生林的土壤质量随年平均降雨量的增加而上升,植被恢复对土壤质量的提升率与年均温和年平均降雨量呈正相关关系。阐明了在一定范围的气候变化下进行植被恢复可以显著提升喀斯特地区土壤的气候韧性,揭示了喀斯特地区植被恢复对土壤质量的提升主要是由于提高了土壤碳氮养分含量及改善了土壤微生物群落结构,这为全球气候变化背景下喀斯特退化土地生态恢复和管理提供了理论依据。     

气候和放牧对锡林郭勒地区植被覆盖变化的影响

基于锡林郭勒盟15个气象站点1981-2007年的逐月气温、降水量数据及各旗县的牲畜头数,在ArcGIS软件的支持下,分析气候干燥度和牲畜密度的空间分布,结合1981-2007年的逐旬归一化植被指数（NDVI）数据,对研究区植被覆盖变化的驱动因素进行分析.结果表明： 研究期间,锡林郭勒盟气候干燥度与植被覆盖状况之间存在良好的线性回归关系;NDVI与牲畜密度之间存在良好的二项式回归关系,随着NDVI值的升高,牲畜密度先增加后降低;植被覆盖状况与干燥度和牲畜密度呈复线性相关关系,其中,NDVI与干燥度呈正相关,与牲畜密度呈负相关,且干燥度对NDVI的影响远大于牲畜密度对NDVI的影响.     

Spatial-based assessment of land use,soil erosion,and water protection in the Jeneberang valley,Indonesia

Soil erosion by water is considered as one of the most significant forms of land degradation that affects sustained productivity of agricultural land use and water quality. It is influenced by a considerable number of factors (including climate, soil, topography, land use and types of land management), so that the information on the spatial distribution of soil erosion rate and its related effects can be effectively employed as a baseline data for land use development and water protection. The principal aim of this study is three-fold: (i) to map existing land use; (ii) to assess and map the spatial distribution of average annual rate of soil losses in the study area; (iii) to evaluate spatial matching between existing and proposed land use including a distance analysis from the water body (the Bili-Bili Dam). An analytical procedures used, respectively, include supervised classification of satellite imagery, application of RUSLE (Revised USLE), and overlay analysis in a raster GIS environment, utilising available information in the region covering some parts of Jeneberang catchment, South Sulawesi, Indonesia. The results suggest that the outputs of this study can be used for the identification of land units on a cell-basis with different land use types, rate of soil loss, inconsistency between proposed and planned land use, as well as the threat of land degradation to the main river and the dam. The analytical procedures developed in this research may be useful in other areas, particularly in the studies related to the assessment and mapping of land use and erosion for the importance of sustainable land use at a relatively large area.     

The impact of agricultural management on soil aggregation and carbon storage is regulated by climatic thresholds across a 3000 km European gradient

Organic carbon and aggregate stability are key features of soil quality and are important to consider when evaluating the potential of agricultural soils as carbon sinks. However, we lack a comprehensive understanding of how soil organic carbon (SOC) and aggregate stability respond to agricultural management across wide environmental gradients. Here, we assessed the impact of climatic factors, soil properties and agricultural management (including land use, crop cover, crop diversity, organic fertilization, and management intensity) on SOC and the mean weight diameter of soil aggregates, commonly used as an indicator for soil aggregate stability, across a 3000 km European gradient. Soil aggregate stability (−56%) and SOC stocks (−35%) in the topsoil (20 cm) were lower in croplands compared with neighboring grassland sites (uncropped sites with perennial vegetation and little or no external inputs). Land use and aridity were strong drivers of soil aggregation explaining 33% and 20% of the variation, respectively. SOC stocks were best explained by calcium content (20% of explained variation) followed by aridity (15%) and mean annual temperature (10%). We also found a threshold-like pattern for SOC stocks and aggregate stability in response to aridity, with lower values at sites with higher aridity. The impact of crop management on aggregate stability and SOC stocks appeared to be regulated by these thresholds, with more pronounced positive effects of crop diversity and more severe negative effects of crop management intensity in nondryland compared with dryland regions. We link the higher sensitivity of SOC stocks and aggregate stability in nondryland regions to a higher climatic potential for aggregate-mediated SOC stabilization. The presented findings are relevant for improving predictions of management effects on soil structure and C storage and highlight the need for site-specific agri-environmental policies to improve soil quality and C sequestration.     

气候变化背景下全球陆地干湿变化研究综述

气候变化背景下,全球水循环加剧,出现了大气变干与植被变绿等陆地干湿变化趋势的解耦现象,旱区面积变化也存在争议。为回答上述问题,在梳理常见干湿指标变化趋势与驱动因素的基础上,根据指标变化方向对其进行归类,然后从机理角度解析影响不同指标趋势耦合或解耦的关键要素,并提出未来干湿变化研究展望。结果表明,气候变化背景下,饱和水汽压差、干燥度指数和土壤水分指标显著变干,植被绿度和生产力显著变湿(增加),降水、径流、陆地水储量和其他复合指标区域分异明显、但整体趋势不显著。二氧化碳浓度增加、气温升高和土地利用变化是导致不同指标趋势分异的重要因素,不同指标的趋势分异也解释了旱区面积评估在不同维度上的差异。未来研究中应开展干湿变化的综合评估,其综合性主要体现在以下四个方面：1)关注大气-生态-水文多维度评估;2)解析自然与人类双重压力下,不同维度要素间的关联、互馈过程,及其对系统干湿演变的促进、限制与调节作用;3)重视干湿演变程中的极端灾害事件和空间上以旱区为代表的气候变化敏感性区域;4)构建以脆弱性评估与适应性治理为核心的气候变化应对路径。     

土壤碳氮特征沿干旱梯度时空格局及对气候变化的响应——基于中国生态系统研究网络(CERN)长期定位监测数据

土壤碳氮含量及其化学计量特征是表征生态系统碳汇能力和土壤质量的重要指标,在支撑生态系统结构功能以及缓解气候变化中起着关键作用。利用中国生态系统研究网络(CERN)长期定位监测数据,分析了土壤碳氮特征沿干旱梯度的时空规律及其对气候变化的响应。结果表明：空间上,典型荒漠草原生态系统随着干旱加剧,土壤有机碳和全氮含量减少,土壤有机碳对干旱响应的敏感性降低,而土壤全氮对干旱响应的敏感性增加,土壤有机碳随土壤全氮含量的增加而增加。时间上,2005—2018年,荒漠草原生态系统土壤有机碳和全氮含量变化速率沿干旱梯度表现出由负转正的增加趋势,其中,干旱区呈减少趋势,半干旱和半湿润地区呈增加趋势,鄂尔多斯站和沙坡头站呈显著增加趋势。从影响因素来看,土壤碳氮特征对降水量增加的敏感性沿干旱梯度呈现出先增强后减弱的“上凸”抛物线趋势,温度变化对土壤碳氮特征的调控没有表现出明显的干旱梯度效应。土壤碳氮比、土壤有机碳含量、土壤全氮含量对降水量和平均温度变化响应的敏感性均依次降低。不同干旱梯度土壤碳氮特征的变化规律为未来气候变化下生态系统结构与功能预测提供科学依据。     

Performance evaluation and cost assessment of a key indicator system to monitor desertification vulnerability

A number of studies have dealt with the assessment of potential and actual desertification risk using composite indices. The Environmental Sensitivity Areas (ESA) approach, developed in the framework of MEDALUS project funded by the European Community, is one of the most used procedures to monitor land vulnerability to degradation in the Mediterranean region. The final output of this procedure is an index (ESI) composing four indicators of climate, soil, vegetation, and land management based on 14 elementary variables. Although applied to a number of case studies throughout southern Europe, northern Africa and the Middle East, the performance of this monitoring system has never been assessed. The present study evaluates the robustness of the ESI through an original procedure incorporating sensitivity analysis and data cost analysis. For each variable, the standard error of the estimate, the correlation coefficient with the ESI, the sensitivity score, and the estimated costs of data collection and handling were calculated in order to evaluate the stability of the final index and the relative importance of each composing variable. The overall performance of the ESI was computed by averaging the score of the four indicators. Variables such as vegetation cover, climate aridity, rainfall, and the degree of land protection provided the largest contribution to the ESI. The illustrated approach is suited to evaluate the overall performance of a set of variables composing a synthetic index. Moreover, to our knowledge, this is the first attempt to consider explicitly the monetary costs of data collection and handling within a composite index evaluation procedure.     

1980—2015年秦岭地区景观格局变化及其对人为干扰的响应

了解景观格局变化及其对人为干扰的响应对于生态系统保护和管理具有重要意义.本研究利用秦岭地区1980—2015年土地利用数据,基于景观格局指数和地表覆盖分类系统,构建景观格局脆弱度指数和人为干扰度,研究了秦岭地区景观格局时空变化及其对人为干扰的响应.结果表明: 1980—2015年,秦岭地区景观破碎化程度逐渐增加,景观形状变得复杂,景观聚集度、连通性降低,景观格局指数空间分布呈现明显的地形分异特征;景观格局脆弱性整体呈下降趋势,其中,低脆弱区空间格局变化比较明显,主要以西安市、汉中市为中心向周围区域扩张;景观格局人为干扰程度逐渐增加,空间分布表现为东部高、西部低,北坡高、南坡低,周边高、中间低;人为干扰度越大,景观格局脆弱度、斑块密度、Shannon多样性指数越大,聚集指数、最大斑块指数越小;人为干扰程度对景观格局脆弱度影响逐渐减弱,对Shannon多样性指数、最大斑块指数的影响逐渐增强,而对斑块密度、聚集指数的影响变化不明显.