Integration of remote sensing techniques for monitoring desertification in Mexico

Desertification is considered one of the most serious threats to arid, semiarid, and sub-humid environments. In this study, several remote sensing techniques were integrated for monitoring desertification in a semiarid region of the central Mexican plateau (state of Querétaro). Landsat TM images were used to compute the Normalized Difference Vegetation Index (NDVI), Bare-Soil Index (BSI), and albedo (α). A change vector analysis (CVA) examined changes in the direction and magnitude of indicators during the 1993–2011 period in order to detect degradations or improvements in land conditions over a period of time. In addition, a desertification degree index (DDI) was applied based on the NDVI–α relationship. The results indicated that in the semiarid zone of the state of Querétaro, 48.3% of land use corresponds with agricultural areas; 2.7% of the area does not present any degree of desertification, while 49% presents the following degrees of desertification: 5.5% extreme, 10.9% severe, 18.9% moderate, and 13.7% low. The DDI applied in this approach for evaluating this phenomenon at the regional and municipal level is an effective tool for identifying areas at risk of desertification, in addition to monitoring changes in the degree or direction of desertification.     

内蒙古自治区沙漠化敏感性时空演变格局和趋势分析

以内蒙古自治区为研究区,基于压力-状态-响应模型(PSR)分析框架,耦合空间距离指数模型(SDIM)构建土地沙漠化敏感性评价体系(LDSES),结合沙漠化敏感性时空演变图谱,定量探讨内蒙古自治区土地沙漠化敏感性在2000年、2005年、2010年、2015年、2020年期间的时空演变,并引入元胞自动机-马尔科夫(CA-Markov)模型模拟沙漠化敏感性未来演变机制,进而采用地理探测器揭示了前20 a演变进程中主要驱动因子对其演变的影响特征及解释力。结果表明：(1)内蒙古自治区沙漠化敏感性整体上呈现由东北向西南递增的趋势,低敏感区位于大兴安岭和阴山山脉周边林草地覆盖区,高敏感区则位于西南部的巴丹吉林沙漠、腾格里沙漠、乌兰布和沙漠、库布其沙漠、毛乌素沙漠等沙地和戈壁地区;(2)从沙漠化敏感性时空演变上来看,研究期间沙漠化敏感性改善的区域,占总面积的30.65%,沙漠化敏感性恶化的区域,占总面积的4.48%,沙漠化敏感性类型维持稳定不变的区域占总面积的52.72%,整体来看土地沙漠化潜力逐渐降低,土地生态质量逐渐好转;(3)2030年沙漠化敏感性模拟结果显示未来10年沙漠化敏感性以低度敏感为...     

藏北那曲地区草地退化动态评价

利用1982—2000年NOAA/AVHRR 第1通道、第2通道和NDVI的旬资料反演得到的藏北那曲地区历年植被覆盖度、年最大牧草鲜质量和6—9月平均改进型土壤调节植被指数,分析了近20年来那曲地区草地荒漠化的动态变化规律.结果表明：以草地荒漠化评价“基准”和5年滑动平均的方法,得到那曲地区近20年平均草地退化面积占土地总面积的43.1%,草地退化面积总体呈减少趋势,其中前10年呈减少趋势,后10年呈增加趋势,西部地区的退化面积大于其它地区.在气温、降水、潜在蒸散、水汽压、风速、日照时数、降水蒸散比和温度降水比8个气候因子中,潜在蒸散量对草地退化面积的影响最显著.     

Impact of land use intensity on sandy desertification: An evidence from Horqin Sandy Land,China

It has been widely accepted that high land use intensity contributes to sandy desertification in Northern China. However, it is surprising that it is even not easy to find an explicit definition and proper indicator for the term “land use intensity” in the sandy desertification related literatures. To better understand the association between sandy desertification and its driving factors, especially in the context of the synergistic roles of both climatic and anthropogenic variables, an indicator for land use intensity was developed in this paper for quantifying the relative role of land use output on different kinds of vegetation cover. The results indicated land use intensity increased rapidly from 1980 to 1995, obviously decreased from 1995 to 2000, and increased slowly after 2000 as a result of the continued increase of socioeconomic pressures and the fluctuating changes in vegetative cover.An ARDL model was established and applied to analyze the correlation between the area of bare sand land and land use intensity with the influence of annual precipitation in temporal dimension. The area of bare sand land was significantly affected by land use intensity in the long run. However, in the short run, the area of bare sand land was mainly impacted by the auto-correlation effect of itself in temporal dimension and by the annual precipitation. The improvement of the sand dunes obviously reduced the risk of sandy desertification under the condition of specific land use intensity.Before analyzing the correlation between land use intensity and sandy desertification, specific skills were applied to improve the model, including data interpolation and regression verification, since there would be regression biases resulting from the acquisition and processing of time-series data of different sources. Results showed that the area of bare sand land (S_t)and the land use intensity (LI_t) were time-independent. Lag terms of these two variables were added to improve original model.Changes in socioeconomic pressures and ecological restoration projects had obvious influences on land use intensity. Along with the steady increase of socioecological pressures on land and the changes in vegetative cover resulting from various ecological protection strategies and ecological restoration projects, shifts in land use intensity followed a different trend with the population and the social-economic demands. Nonetheless, the continuous increase of socioeconomic demands will increase land use intensity in the long run, so that the risk of sandy desertification remains high.     

呼伦贝尔沙地45年来气候变化及其对生态环境的影响

采用数理统计和对比分析方法,对近45年呼伦贝尔沙地气象观测资料和草场沙化、退化面积、植被状况等资料进行了分析。结果表明:呼伦贝尔沙地总体气候暖干化趋势显著;气温逐年升高、降水量减少、蒸发量增加和极端气候事件增多,使流动沙地面积不断增加,植被盖度下降。卫星遥感监测和全国沙漠化普查结果进一步表明,呼伦贝尔沙地的沙漠化正在扩展,生态环境正在恶化。逐年减少的大风日数和沙尘暴日数有利于该地区生态的保护与建设。20世纪80年代以来,沙区各级政府加大了对沙化的治理力度,沙地局部植被恢复较快。     

呼伦贝尔沙地45年来气候变化及其对生态环境的影响水

采用数理统计和对比分析方法,对近45年呼伦贝尔沙地气象观测资料和草场沙化、退化面积、植被状况等资料进行了分析。结果表明：呼伦贝尔沙地总体气候暖干化趋势显著;气温逐年升高、降水量减少、蒸发量增加和极端气候事件增多,使流动沙地面积不断增加,植被盖度下降。卫星遥感监测和全国沙漠化普查结果进一步表明,呼伦贝尔沙地的沙漠化正在扩展,生态环境正在恶化。逐年减少的大风日数和沙尘暴日数有利于该地区生态的保护与建设。20世纪80年代以来,沙区各级政府加大了对沙化的治理力度,沙地局部植被恢复较快。     

沙地油蒿群落覆盖度的遥感定量化研究

鄂尔多斯地区荒漠化与沙地植被覆盖度有紧密的关系。用 NOAA卫星数据对沙地植被覆盖度进行动态监测可以为认识该地区的荒漠化动态变化及过程提供丰富的信息。通过分析沙地反射机理 ,建立了沙地油蒿(Artemisia ordosica)群落盖度与修正后的土壤调节植被指数 (MSAVI)之间的关系模型。然而 ,卫星数据用于该关系模型之前 ,必须进行处理。本文首先用裸沙土壤线法校正大气影响 ,然后 ,用 MSAVI消除土壤背景影响     

1995-2018年石羊河流域下游荒漠化动态变化

以石羊河流域下游甘肃省民勤县为研究区,选取1995、2000、2005、2010、2015、2018年6期遥感影像作为数据源,利用RS和GIS理论和方法,基于归一化植被指数(NDVI)和地表反照率(Albedo)建立Albedo-NDVI特征空间,构建荒漠化差值指数,对民勤县荒漠化动态变化进行分析.结果 表明:石羊河流...     

荒漠化治理中生态系统、社会经济系统协调发展问题探析——以中国北方半干旱荒漠区沙漠化防治为例

全球变暖导致的区域干旱使得干旱区水资源日益匮乏,而迅速增长的人口和社会经济发展进一步加剧水资源危机,使得有限的水资源成为全球沙漠化防治瓶颈,严重制约了沙化土地治理进程,影响了联合国"土地退化总面积零增长"目标的实现,也影响了中国社会经济的可持续和协调发展。传统的沙化土地治理生物措施重视植被盖度增加,忽视生态系统其他要素,如土壤水分、养分等与植被的相互关系,导致一些治理措施相对简单,生态系统不能协调发展。而沙化土地治理的物理措施和化学措施由于忽视了沙区社会和经济效益,其可持续性也受到科学家质疑。近期获批的国家重点研发计划项目"中国北方半干旱荒漠区沙漠化防治关键技术与示范"(2016YFC0500900)拟针对此问题开展研究,以沙化土地稳定恢复为首要目标,在认识半干旱荒漠区沙化土地正/逆过程演变机制和荒漠生态系统稳定性的基础上,研究沙化土地稳定恢复的生态阈值;以毛乌素沙地、库布齐沙漠东部、科尔沁沙地西部和呼伦贝尔沙地为典型区,针对不同沙化土地特点,研发防沙治沙关键技术,开展模式优化和试验示范;在防沙治沙模式与工程效益评估基础上,集成产业化技术体系,为国家防沙治沙工程建设提供理论基础与技术支撑。     

基于SNIC-CNN-SVM模型的京津风沙源二期工程区土地利用/土地覆盖遥感识别研究

稀疏植被覆盖(草地、沙地、戈壁)演变能够直接表征区域生态环境和人类活动的动态影响变化。但由于大尺度稀疏植被区一般都具有地理跨度大,景观结构复杂多样,破碎化程度高,现有地表覆盖分类产品针对性不足等问题,使得该区域内林草沙的遥感提取难度较大,精度普遍偏低,直接制约生态效应评价模型的应用效果。因此,以典型大尺度稀疏植被区——京津风沙源治理二期工程区为研究区,研建了SNIC-CNN-SVM(SCS)模型,实现了大尺度稀疏植被区林草沙典型要素的信息自动提取和主要土地利用/土地覆盖类型识别。研究结果表明：1)引入惩罚性机制优化后的SNIC分割算法,有效提升了稀疏植被区与沙地区的边界区分度,有助于分类精度的提升;2)基于改进SNIC-CNN-SVM模型方案的研究区总体分类精度达89.41%,较优化前提高了11.17%,特别是乔、灌、草、沙地和戈壁的分类识别精度显著提升,表明该优化方案在以研究区为代表的稀疏植被区域分类中具有较好的应用效果和推广价值;3)分类结果显示,2020年工程区草地面积最大,占到了一半以上(51.52%),沙地占比11.96%,稀疏植被覆盖(草地、沙地、戈壁)区域占比68.68%...     

西南喀斯特地区石漠化时空演变过程分析

喀斯特地区石漠化对当地社会经济的可持续发展有严重的阻碍作用,因此,研究喀斯特石漠化时空特征及演变规律,对石漠化治理有着重要的意义。以西南八省为研究区,利用归一化差分植被指数（Normalized Difference Vegetation,NDVI）、净初级生产力（Net Primary Productivity,NPP）、地表反照率（Surface Albedo）和坡度（Slope）数据,借助ArcGIS等软件平台,分析石漠化在不同的坡度、土地利用和生态保护区内的变化。结果显示：（1）轻度和中度石漠化是西南主要的石漠化类型。从空间分布来看,石漠化发生分布面积最广的是贵州,其次为云南和广西。（2）从不同土地利用来看,2000-2015年间无石漠化面积最多,潜在石漠化次之。石漠化主要发生在耕地和林地两种土地类型上,其他用地上石漠化发生面积最少,但是极重度石漠化在其他用地上的发生比例很大,平均在11%左右。（3）从不同坡度来看,石漠化严重程度不随坡度的增加而加剧,在坡度6°-25°之间石漠化发生面积最大。（4）从生态保护区来看,2000和2015年西南喀斯特生态保护区是石漠化面积分布最多的区域,分别为27481.86 km²和21738.65 km²。最少的是大别山山地生态功能保护区,从变化量来看,增加最多的是三峡库区,增加1641.22 km²,减少最多的是西南喀斯特生态功能保护区,减少5743.22 km²。（5）利用NPP、NDVI、地表反照率和坡度能较精准的反演石漠化,其反演权重依次为0.33、0.42、0.15和0.1。研究时段内,西南生态环境逐渐得到改善。     

Long-term desertification process monitoring and driving factors analysis in rare earth mining area

With the exploitation of rare earth elements (REE) in southern China, desertification has become a serious ecological problem in this region. To accurately understand the desertification process in mining areas and formulate targeted ecological restoration programs, taking the Lingbei mining area in Ganzhou City, Jiangxi Province as the study area, we explored desertification information extraction methods, desertification dynamics monitoring, and desertification drivers in REE mining areas using multisource data from 1986 to 2021. The results show that from the method of extracting desertification information, Random Forest is the prominent (83.33%), followed by Albedo–NDVI (Normalized Difference Vegetation Index) space (74.44%), and thirdly Linear Spectral Mixture Model (65.56%). From 1986 to 2021, the desertification land area in Lingbei mining areas first increased and then decreased, showing a reverse trend, but it has not recovered to the pre-mining level. The government's ecological reclamation measures are the key factors for the restoration of desertification land. There are still 17.81 km² areas that have not been restored, of which 2.16 km² are at the level of severe desertification. Moderate desertification and light desertification have not been completely curbed, which needs continuous attention. Vegetation coverage has the highest explanatory power to the distribution of land desertification in mining areas, followed by land use classification, indicating that human activities have a great influence on the spatial differentiation of land desertification in mining areas, and it is necessary to pay attention to regional balanced and sustainable development in the future.     

土地退化零增长评估——以蒙古高原为例

由于全球气候变化以及人类活动对生态系统的影响加剧,干旱半干旱区的土地退化愈发严重。为了防止土地退化,联合国防治荒漠化公约(UNCCD)提出了土地退化零增长(LDN)的目标。首先介绍LDN的概念与评估方法,接下来以蒙古高原为例,采用土地覆盖、土地生产力和土壤有机碳3个核心指标,评估2001-2020年蒙古高原LDN目标的实现情况。研究结果表明,相对于基线期(2001-2010年)的生态系统状态,评估期内(2011-2020年)新增恢复区域的面积(10.83×10⁴km²)大于新增退化区域的面积(7.77×10⁴km²),蒙古高原在2020年已实现土地退化零增长目标。两个十年中,恢复面积比退化面积分别超出6.87×10⁵km²(2001-2010年)和9.44×10⁵km²(2011-2020)。但是现有的LDN评估方法存在指标和方法不完善以及数据源不确定等问题,未来研究需进一步优化和发展评估指标与方法。此外,目前以LDN为概念框架的实证性研究还比较少,区域评估有助于评判区域土地退化状况和识别关键区域,从而制订空间明晰的生态恢复策略。     

整治"三滥"是从源头遏制生态脆弱地区土地荒漠化的必由之路——以科尔沁沙地为例

针对中国土地荒漠化的现状和关键问题,以科尔沁沙地为例,阐述了荒漠化的发展历程、主要动因与未来趋势。科尔沁沙地正处在现代土地荒漠化过程之中,导致快速发展的荒漠化动因主要是源于人们不合理的土地利用方式,即滥垦、滥牧和滥伐(简称“三滥”);而在各种利农政策下,滥垦可能会重新滋生和蔓延,是非常值得借鉴的历史教训。本文应用复合生态系统的观点剖析了“三滥”与荒漠化的关系,并据此提出从源头减轻土地压力的6项对策。     

毛乌素沙地南缘沙漠化临界区域土壤养分的空间异质性

毛乌素沙地南缘沙漠化临界区域是沙地-草地景观界面的关键部位,研究该区域土壤养分的空间格局和生态学过程,对于土地沙漠化的机理研究具有重要的意义。采用经典统计与地统计学相结合的方法,通过半变异函数及其模型、克里格局部插值估计、空间分布图等研究了毛乌素沙地南缘沙漠化临界区域土壤养分的空间异质性特征。结果表明:研究区土壤速效钾含量符合球状模型,全氮和速效磷含量符合指数模型;速效钾含量具有强空间自相关性,其结构方差比为0.882,而全氮和速效磷含量表现为中等程度的空间自相关性,其结构方差比分别为0.501和0.514;3种土壤养分空间自相关距离存在差异,其中全氮和速效钾的变程均为511m,而速效磷的变程为143m;3种土壤养分的分布格局呈现明显的空间规律性,从牛枝子群落到黑沙蒿群落,速效钾和速效磷含量先降低后升高,与研究区的界面变化过程一致,而全氮含量逐渐降低,与研究区的植被覆盖度变化一致;3种土壤养分的标准差都较小,Kriging插值结果比较可靠。     

Can mobile sandy land be vegetated in the cold and dry Tibetan Plateau in China?

Desertification has taken place in the overgrazed grassland of the Tibetan Plateau, China, and the area of mobile sandy land has increased in recent decades. The challenging problem about desertification control is how to restore the vegetation of mobile sandy lands caused by severe desertification. Sand drifting is now regarded as the limiting factor of vegetation restoration in such lands. The initial phase of vegetation restoration is plant colonization, but it is often aborted due to sand drifting, and then vegetation restoration fails to proceed. For the sake of revegetation, the first step is to stop sand drifting to ensure plant colonization. In the northeastern Tibetan Plateau, China, feasible approaches have been found through long-term experiments, and the vegetation is being restored satisfactorily with these approaches in experimental sandy lands. The approaches comprise three types: enclosure, mechanical barriers and biological barriers. Different sandy lands require dissimilar combinations of these approaches. Enclosures may be adequate to revegetate inter-dunes or degraded grassland even in cold regions like the Tibetan Plateau, China, but it is deficient for revegetation of the shifting sand dunes unless mechanical and biological barriers are established simultaneously.     

Can mobile sandy land be vegetated in the cold and dry Tibetan Plateau in China?

Desertification has taken place in the overgrazed grassland of the Tibetan Plateau,China,and the area of mobile sandy land has increased in recent decades.The challenging problem about desertification control is how to restore the vegetation of mobile sandy lands caused by severe desertification.Sand drifting is now regarded as the limiting factor of vegetation restoration in such lands.The initial phase of vegetation restoration is plant colonization,but it is often aborted due to sand drifting,and then vegetation restoration fails to proceed.For the sake of revegetation,the first step is to stop sand drifting to ensure plant colonization.In the northeastern Tibetan Plateau,China,feasible approaches have been found through long-term experiments,and the vegetation is being restored satisfactorily with these approaches in experimental sandy lands.The approaches comprise three types:enclosure,mechanical barriers and biological barriers.Different sandy lands require dissimilar combinations of these approaches.Enclosures may be adequate to revegetate inter-dunes or degraded grassland even in cold regions like the Tibetan Plateau,China,but it is deficient for revegetation of the shifting sand dunes unless mechanical and biological barriers are established simultaneously.     

科尔沁沙地荒漠化及生态恢复研究展望

评述了科尔沁沙地荒漠化及其生态恢复的研究,从科学研究动态和生态环境退化以及恢复研究的现实需要两方面论述了科尔沁沙地荒漠化与生态恢复研究的若干核心问题;植被过程研究,生态水文过程研究,景观过程研究,科尔沁沙地区域环境评估和预测与生态恢复研究。     

沙质草地生境中大型土壤动物对土地沙漠化的响应

沙质草地沙漠化过程中土壤动物群落结构变化是沙漠化生物过程中的一个重要方面,对于掌握沙漠化过程中生物退化规律和提出合理沙漠化防治对策具有重要指导作用。选取处于不同沙漠化阶段的流动沙地、半流动沙地、半固定沙地、固定沙地和丘间低地5种生境类型,采用手拣法对其大型土壤动物群落进行了调查。共获得36个动物类群,属于8目32科,优势类群为蚁科,常见类群有22个类群,两个类群的个体数共占群落个体总数的93.33%;稀有类群有13个类群,其个体数占群落个体总数的6.67%。结果显示,丘间低地、固定沙地、半固定沙地和半流动沙地大型土壤动物群落个体数量、类群数和多样性显著高于流动沙地(P<0.05);固定沙地大型土壤动物生物量显著高于其它生境类型(P<0.05);沙质草地严重沙漠化显著地影响大型土壤动物多样性及其生物量。并且,不同土壤动物类群个体对不同沙漠化阶段生境的适应性存在一定差异,产生了不同的响应模式。土壤有机碳和酸碱度以及土壤含水量差异是影响大型土壤动物类群分布与生长的主要因素。研究表明,固定沙地是大型土壤动物的适宜沙地生境,具有较多的个体数量和较高的生物量;丘间低地、半固定沙地、半固定沙地和流动沙地影响大型土壤动物存活,其个体数量和生物量较低。     

宁夏红寺堡扬黄灌区土壤沙化和盐渍化及其相互关系

采用控制取样和典型取样相结合的方法,对比分析了红寺堡扬黄灌区玉米地和枸杞地、未利用地0 ～40 cm分层土壤质地、盐渍化特征、阳离子交换量(CEC)值及其相关关系.结果表明:控制取样条件下,除未利用地0～10 cm土壤含盐量(TS)达1.74 g·kg-1外,3种利用方式下0～40 cm TS在0.69～1.30 g· kg-1之间变化,盐化特征不明显;枸杞地20～40 cm土壤钠吸附比(SAR)和土壤碱化度(ESP)分别达到12.18％和l4.1％;玉米地0～20 cm粘粉粒和(CPS)为13.5％,构杞地O～40 cm CPS达37.3％.控制取样条件下,20～40 cm土层玉米地土壤碱化和沙化指标间显著相关;典型取样条件下,上述相关性消失,但CEC与沙化指标及盐渍化指标均显著相关.不同土地利用方式下灌区土壤沙化和盐渍化呈复杂的交互关系,CEC可以作为土壤环境质量变化的综合指示因子.