基于日光诱导叶绿素荧光探测植被光合对气象干旱的响应

干旱是世界范围内最常见、最复杂的气象灾害,一定程度上会削弱陆地生态系统的碳汇功能。开展植被对干旱响应的研究并选择敏感的干旱探测因子,有助于掌握干旱对植被的影响规律、理解植被对干旱胁迫的响应过程和机理。本研究以日光诱导叶绿素荧光（SIF）数据和标准化降水蒸散发指数（SPEI）为基础,利用最大相关系数法分析中国区域内2000-2018年生长季植被光合对气象干旱的响应,比较不同干旱梯度、不同植被对干旱响应的敏感性以及SPEI响应时间尺度的变化特征。结果表明：（1）SIF与SPEI具有很好的相关性,显著正相关的面积达到75.05%,主要分布在东北、西南和青藏高原地区,且大部分地区对SPEI的响应时间尺度以中短期为主。（2）SIF在春季对SPEI显著相关的区域占比最少,夏季达到最高,秋季又略有下降。对干旱响应的时间尺度在春季以短期为主,而夏季响应时间尺度长的区域较春季有所增加。（3）半干旱区对干旱的敏感性最强,干旱区最弱,不同气候区对干旱的响应时间尺度均以短期为主。（4）研究所选植被类型均能较早地对干旱做出响应,其中,草地对干旱最敏感,林地和农田相对较弱,阔叶林比针叶林对干旱更敏感。研究结果表明...     

特征优化结合随机森林算法的干旱区植被高光谱遥感分类方法

针对高维光谱纹理特征空间的降维和特征优化算法结果的不确定性问题,该研究在提取多尺度纹理图像构建高维光谱纹理特征空间的基础上,将遗传算法（genetic algorithm,GA）、粒子群优化算法（particle swarm optimization,PSO）等传统特征优化算法和广义正态分布优化算法（generalized normal distribution optimization,GNDO）、原子搜索算法（atom search algorithm,ASO）、海洋捕食者算法（marine predators algorithm,MPA）等特征优化算法与随机森林（random forest,RF）图像分类算法相结合,提出了GA-RF、PSO-RF、GNDO-RF、ASO-RF和MPA-RF算法,并应用于青海省海西蒙古族藏族自治州都兰县宗加镇附近区域资源一号02D（ZY1-02D）高光谱数据的植被类型分类。结果显示,在高光谱反射率数据基础上加入多尺度纹理特征使总体分类精度（overall accuracy,OA）提升了8.02个百分点。与传统RF方法相比,提出算法的植被分类 OA提升了1.32～2.40个百分点,其中MPA-RF方法取得了最高的分类精度,OA和 Kappa系数分别为88.92%和0.86。研究表明从不同窗口大小、窗口移动方向提取的纹理图像有利于区分不同的植被与地物类型,在光谱特征基础上加入多尺度纹理特征能有效提升植被识别精度。以迭代优化的方式将特征优化算法与图像分类算法相结合,缓解了优化算法结果的随机性,克服了高维特征的休斯效应,提高了植被分类精度。该研究为高光谱遥感植被分类中特征提取、特征优化与分类算法选择提供了思路。     

Coniferous afforestation increases soil carbon in maritime sand dunes

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha^?1 y^?1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha^?1 under pine and 27 Mg ha^?1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha^?1 y^?1) than on ridges(29 Mg ha^?1 y^?1) and bottoms (12 Mg ha^?1 y^?1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.     

陕北地区退耕还林十年植被恢复变化分析——以子长县为例

以2000年和2010年ETM+遥感数据为数据源,借助ArcGIS和ERDAS软件平台对子长县退耕还林以来的植被覆盖度﹑土地利用变化及生态环境质量进行了定量分析,结果表明:2000—2010年植被覆盖度由劣等和差等向中等和良等转变,其中良等盖度面积比例由2010年的2.30%增加到51.30%;主要植被类型中林地面积增长幅度最大,增长面积占土地总面积的23.73%;退耕还林十年间子长县整体生态环境质量得到改善,生态环境质量指数上升0.052 8。     

Soil respiration as affected by vegetation types in a semiarid region of China

There are variations in soil respiration across vegetation types; however, it is unclear which factors are mainly responsible for the variations. A field experiment was conducted in 2008 and 2009 in a semiarid region of China to investigate the daytime and monthly variation of soil respiration across vegetation types and to determine the factors controlling the variation. An automated portable soil carbon dioxide (CO₂) flux measurement system was used to measure the soil respiration in shrubland, grassland, fallow land, and cropland during the growing periods. The results showed that the relative daytime variation amplitude of soil respiration in the fallow land and cropland was as small as that of shrubland and grassland during July, but greater than that of shrubland and grassland during August and October. A hysteresis effect for the relationship between the daytime soil respiration and daytime soil temperature was observed for all four vegetation types. There was also a hysteresis effect for the relationship between the daytime soil respiration and daytime air temperature for the grassland. Over the study period, the monthly soil respiration rates of the fallow land and cropland were statistically comparable and significantly lower than those of the shrubland and grassland, with the exception of August, during which the monthly soil respiration of the cropland was as great as that of shrubland and grassland. The factors responsible for the monthly soil respiration variation across the vegetation types differed from month to month. In general, the soil temperature and soil water content were mainly responsible in August and September; however, the root biomass predominated in July and October. The results are valuable for accurately estimating regional carbon fluxes by considering the temporal variability of the soil respiration variation across vegetation types in the Loess Plateau of China.     

LOCAL PERCEPTIONS OF WOODY VEGETATION DYNAMICS IN THE CONTEXT OF A ‘GREENING SAHEL’: A CASE STUDY FROM BURKINA FASO

After decades of drought in the Sahel, several studies have reported a ‘(re)greening’ of the area. However, most of these studies were based on large scale climatological or remotely sensed observations, with little or no ground truthing. The aim of this study was to assess the local perceptions of the distribution of socio‐economically important tree species in the Sub‐Sahel of Burkina Faso. Semi‐structured interviews were performed with 87 groups of informants from 20 villages belonging to three ethnic groups (Mossi, Fulani and Samo). Univariate and multivariate statistics were used to compare perceptions between the targeted ethnic groups. According to the locals, more than 80 per cent of the 90 listed species were declining, with over 40 per cent identified as threatened, including numerous plants of great economic value. Increasing species were mostly drought‐tolerant plants such as Balanites aegyptiaca. A few species were listed as locally extinct. Gender and age did not significantly affect local knowledge, whereas ethnicity did. The major causes of species decline were identified to be drought, deforestation and bushfires. In all ethnic groups, informants observed a southward shift in species distribution. Local perceptions suggest a general decline in woody vegetation. Thus, the alleged (re)greening in the Sahel might not have reversed the degradation of woody species in the area. Data derived from local ecological knowledge were consistent with that of many ecological studies, suggesting the reliability of people's knowledge for obtaining ecological data. Information from this study can be used as baseline for conservation of species identified as threatened. Copyright © 2011 John Wiley & Sons, Ltd.     

DEGRADATION AND RECOVERY PROCESSES IN SEMI‐ARID PATCHY RANGELANDS OF NORTHERN PATAGONIA,ARGENTINA

Vegetation in many arid and semi‐arid shrublands frequently occurs in patches with high plant cover (shrub patches) interspersed in a low‐cover herbaceous matrix (inter‐shrub areas). We hypothesized that (a) livestock grazing is an important determinant of such spatial patterns of vegetation, and (b) redistribution of soil resources associated with shrub patches helps in the recovery of vegetation in inter‐shrub areas. To test these hypotheses, we (a) used line transects to compare spatial variations in vegetation, soil microtopography, and soil physicochemical properties in grazed areas and areas protected from grazing since 1970, (b) added sediment and seeds to inter‐shrub areas, and (c) measured resource redistribution after a wildfire. Results were consistent with the hypotheses. They indicated greater spatial heterogeneity in vegetation, soil microtopography and soil physicochemical properties in grazed areas than in protected areas, and that addition of sediment and seeds or redistribution of soil resources from shrub patches after a wildfire enhanced re‐establishment of vegetation in degraded inter‐shrub areas. As a synthesis, a conceptual model of degradation and recovery processes in semi‐arid shrublands of Northern Patagonia is presented. Copyright © 2011 John Wiley & Sons, Ltd.     

汶川地震灾区归一化植被指数变化监测分析

提取归一化植被指数合成旬最大植被指数,研究地震重灾区域的植被状况.结果表明:1)盆地西部和北部山区,植被在4月下旬到5月底呈现自然生长规律,并且存在一条以旬最大植被指数为标记的稳定边界线来区分盆西山区和盆地农田;2)2008年地震前期,4月下旬的旬最大植被指数好于5月上旬,地震发生的5月中旬,旬最大植被指数在成都平原、德阳和阿坝州交界的山区明显减小,5月下旬,大部分区域旬最大植被指数都在减小;3)2009年5月中旬的旬最大植被指数是最好的,5月下旬,盆地中的旬最大植被指数值减小;4)地震使得在盆西山区和盆地农田之间通过旬最大植被指数表征的稳定边界被破坏.     

黄河三角洲滨海湿地生态修复区春季土壤古菌和细菌群落结构探究

盐地碱蓬是黄河三角洲滨海湿地生态功能的起点和核心,其原生修复在土壤改良和微生物功能恢复方面的作用仍未可知.因此,本研究开展了盐地碱蓬修复土壤的细菌和古菌群落结构分析,借助理化性质检测和高通量手段进行了样品实验室检测.结果发现,滨海湿地土壤均呈碱性(pH=7.92～8.45),盐度含量较高(>30.98‰)且非植被区土壤...     

高寒草甸退化对土壤电导率变化影响的研究

土壤电导率是表征土壤水溶性盐的一个重要指标,可反映土壤盐渍化程度。为了研究高寒草甸退化对土壤电导率的影响,以三江源区未退化高寒草甸和退化高寒草甸为研究对象,系统分析了退化高寒草甸的植被特征和土壤特征与土壤电导率的相互关系。结果表明:高寒草甸退化会对土壤电导率产生显著负影响,且土壤电导率与评价高寒草甸的退化指标植被盖度、地上生物量、土壤有机质、土壤全氮含量表现出一致的变化趋势。因而,认为高寒草甸的退化是会引起土壤电导率的变化,土壤电导率作为土壤盐渍化程度的衡量指标,亦可作为评价草甸退化的客观指标之一。