黄土高原半干旱区天然锦鸡儿灌丛对土壤水分的影响

本文选择黄土高原半干旱区定西地区的一种地带性植被,天然甘蒙锦鸡儿灌丛,将其0～99m深的土壤水分含量与人工柠条锦鸡儿灌丛、人工杏树林、天然草地、放牧荒坡和农地的土壤水分含量进行了比较。结果发现,天然锦鸡儿灌丛在1m以下土壤各层的水分含量均高于人工柠条灌丛和人工杏树林,而与放牧荒坡和农地的土壤湿度接近,略低于农地。天然锦鸡儿灌丛4m以上土层的土壤湿度还明显高于天然草地;天然锦鸡儿灌丛形成的难效—无效水层深度在2m土层以上,而人工柠条灌丛形成的难效无效水层则深达56m,人工杏树林42m,天然草地、放牧荒坡分别为36m和33m,农地1m。     

中国北方干旱半干旱区植被-气候响应关系特征北大核心CSCD

气候变化背景下干旱区植被的时空分布及变化特征,是区域植被恢复和国家自然保护区建设等亟需研究的关键生态环境问题。在建立中国北方干旱半干旱区潜在植被分类及对Holdridge生命地带模型进行修正和拓展的基础上,结合中国气象模拟数据(1981—2020年),引入植被面积转移矩阵、Kappa系数和平均中心模型等方法,对中国北方干旱半干旱区气候要素进行分析并实现了潜在植被定量识别和空间分布格局模拟。结果显示:40年间年降水量、年平均生物温度和可能蒸散率总体均呈上升趋势,研究区存在暖干化现象;研究区共出现6种潜在植被类型,在不同年代际均呈地带性分布;温带荒漠植被、温带草本植被和温带森林植被是主要植被类型,共占总覆盖面积约71%;温带森林植被的面积总体增长最快,平均每10年增加1.1%,温带荒漠植被减少最快,平均每10年减少1.3%;相邻年代际间,各类潜在植被的面积转换关系较为稳定,差别在于转换程度;山地森林植被、温带荒漠植被和温带森林植被的平均中心总体偏移距离大于50 km,除温带荒漠植被,其他植被的平均中心总体均往西移。     

干旱半干旱地区草原灌丛荒漠化及其 生物地球化学循环

干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象, 是草地沙化和荒漠化的一个重要标志。干旱生态系统中, 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中, 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异, 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制, 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。     

干旱半干旱地区草原灌丛荒漠化及其生物地球化学循环

干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象, 是草地沙化和荒漠化的一个重要标志。干旱生态系统中, 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中, 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异, 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制, 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。     

干旱、半干旱区陆气相互作用的研究进展

 对干旱、半干旱地区陆气相互作用的研究进展及发展现状做了总结，并结合近年来在干旱、半干旱地区开展的近10个有关陆气相互作用的大型野外观测试验和具有代表性的土壤水热参数化方案，分析了当前干旱区陆面过程研究中存在的问题，最后探讨了干旱区陆面过程未来的发展趋势。     

基于低空无人机的草原灌丛遥感辨识方法

以位于中国科学院内蒙古草原生态研究定位站灌丛化样地实验平台为研究区,基于低空无人机遥感影像,结合实地调查,开展草原灌丛遥感辨识方法研究。通过对灌丛、草地和裸地归一化植被指数（NDVI）的方差统计分析,确定了裸地与植被的分割阈值为-0.08,并使用该阈值提取植被覆盖区,然后分别利用面向对象的决策树（DT）、贝叶斯（Bayes）、K最邻近（KNN）、支持向量机（SVM）机器学习分类器进行灌丛辨识。研究表明：借助Estimation of Scale Parameter（ESP）最优分割尺度评价工具可以快速确定分割参数,获取灌丛、草地影像对象;利用特征空间优化工具选取了18个的对象特征,可以有效避免盲目选择而导致的计算量增大;通过对不同分类器分类结果的对比和样本数量敏感性实验得出：Bayes分类器精度稳定、无需设置参数,灌丛分类精度最高,总体精度和Kappa系数分别达到92%和0.83,结果与影像地物嵌合最好,能够精确识别单株灌丛;根据Bayes分类器分类结果统计得研究区灌丛盖度为14.74%,平均冠幅为0.6 m²,与样方调查结果基本一致。由于4种分类器的算法特征以及对训练样本数量的敏感性各不相同,因此选择合适的分类器还需根据具体影像的地物特征、空间分辨率和研究区范围来确定。     

干旱半干旱区农田土壤风蚀特征及参数化研究进展

干旱半干旱地区是中国的农业后备战略基地,然而近年来该地区农田土壤风蚀现象严重,沙/尘释放量显著增大,威胁农业的可持续发展和生态系统平衡。目前绝大部分的天气和气候模式仅考虑了沙漠地表起沙,忽视退化农田的土壤风蚀起沙,导致起沙通量模拟存在很大的不确定性。对20世纪50年代以来干旱半干旱区农田土壤风蚀起沙特征及参数化做了详细的分析总结,回顾并梳理了干旱半干旱区农田土壤风蚀观测和数值模拟的研究脉络以及存在的问题,为提高农田起沙的模拟精度提供了有效参考,对中国干旱半干旱区农田土壤风蚀防治、土地荒漠化治理以及理解未来土地利用改变对大气污染的影响具有重要意义。     

灌丛沙丘形成演化及环境指示意义研究的主要进展

干旱半干旱区风沙活动较强烈, 风沙地貌十分发育, 环境演变过程对气候变化响应敏感。由于缺乏高分辨率载体, 在这些地区进行环境变化重建的手段及获得的结果相对贫乏。但是在这些区域发育的灌丛沙丘是风沙堆积体, 其形成演化记录了相对丰富的区域环境演变信息。本文综述了目前在灌丛沙丘形态学特征、发育过程、以及其在区域环境变化重建中的意义等方面的研究进展。我们认为, 灌丛沙丘形成演化研究在揭示干旱区环境演变过程方面有重大的意义, 但还没有形成系统的体系, 这一方面的研究仍有较大的空间。     

荒漠灌丛微生境土壤温度的时空变异特征——灌丛与降水的影响

对干旱区优势固沙灌木柠条群落不同微生境（灌丛外和灌丛下）的土壤温度（0 cm、5 cm、10 cm和20 cm剖面深度）进行了连续测定,对比分析了晴天、降水日与灌丛对其微生境土壤温度时空变异的影响。结果表明:降水和植被灌丛对土壤温度均具有显著影响。在无雨日,受灌丛遮阴影响,灌丛外土壤温度明显高于灌丛下相同深度的土壤温度;在降水日,土壤温度主要受降水影响,降水使土壤温度明显降低,灌丛的影响作用减弱,灌丛下和灌丛外同一剖面深度的土壤温度差异较小。无雨日土壤温度日变化呈单峰型正弦曲线,随剖面深度增加,土壤温度振幅逐渐减小,峰值出现时间滞后,土壤温度垂直分布变化呈现4种典型变化曲线。夜间（日落至日出）柠条灌丛下地表温度（0 cm土壤温度）比灌丛外地表温度略高。降水日土壤温度日变化随降水过程的持续呈逐渐递减趋势,土壤温度垂直分布变化表现为随深度增加而递增的趋势。     

荒漠草原带沙源及灌丛对灌丛沙堆形态的影响

灌丛沙堆是干旱区一种典型的景观类型,经常出现在靠近流沙地带。在地处荒漠草原带的宁夏盐池北部的流沙边缘就发育有典型的白刺(Nitraria tangutorum)灌丛沙堆。本文对不同沙源距离和灌丛生长状况下的白刺灌丛沙堆形态特征进行了研究。结果表明:荒漠草原带白刺灌丛沙堆的高度0.2～4.8 m,90.05%的高度小于3.0 m;体积0.11～805.17 m³,6.08%的体积小于150 m³;面积0.86～333.3 m²,72.26%的小于50 m²。灌丛沙堆长轴长和短轴长、高度和面积、高度和体积、面积和体积间都存在很好的幂函数关系,随着灌丛沙堆高度的增加,其面积和体积也增加。沙源对白刺灌丛沙堆的分布特征有显著影响,灌丛沙堆的高度、面积和体积和沙源距离都有很好的抛物线形关系。白刺灌丛的生长状况对灌丛沙堆的形态特征也有明显的影响,即白刺灌丛生长状况越好,灌丛沙堆的高度、面积和体积也增大。     

High-resolution images reveal rate and pattern of shrub encroachment over six decades in New Mexico, U.S.A.

Encroachment of the shrub Prosopis glandulosa Torr. (honey mesquite) into semi-arid grasslands is a serious concern in the south-western United States, yet little is known about the long-term dynamics of the invasion process. We used ten high-resolution aerial and satellite images taken from 1936 to 1996 to track the population dynamics and spatial pattern of all P. glandulosa greater than 2 m in diameter on a 75 ha area in southern New Mexico.Shrub cover and patch numbers increased from 1936 to the 1970s, then stabilized at 43% cover and 83 patches ha⁻¹. Individual patches were extremely persistent: 95% of the area occupied by shrub patches in 1936 was still occupied in 1996. Recruitment into the 2 m size class was more variable: 0·6–5·2% year⁻¹ (mean 0·8% year⁻¹). Patch-shape complexity increased from 1936 to 1983 as adjacent shrubs merged, and then declined as those clusters filled in and became rounder. Spatial pattern of shrubs showed a distinct trend over time: strongly clustered in 1936 at lag distances up to 250 m, then random arrangement at all scales, and by 1983 pattern was regular at lag distances greater than 100 m. There was no clear relationship with precipitation.The use of remote sensing imagery allowed us to examine one site over time, and revealed patterns in population dynamics and spatial pattern that would not have been visible otherwise. Comparison of field estimates collected in 2001 with 1996 image data suggest that the canopy cover estimates were accurate, but shrub densities were seriously underestimated in the satellite photographs, which do not show shrubs smaller than 2 m diameter. As long as limitations of the imagery are understood, these methods can be applied over a larger and more heterogeneous area to examine environmental correlates of invasion success.     

Dead shrub patches as ecosystem engineers in degraded drylands

A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev.The most impacted shrub species is the Noaea mucronata (Forssk.) Asch.and Schweinf.In a four-year study,we found that herbaceous vegetation growth was greater in the dead shrub patches than in the surrounding inter-patch biocrusted spaces,suggesting that the dead shrub patches encompass improved micro-habitats.However,unexpectedly,the soil moisture in the dead shrub patches was consistently lower than that of the inter-patch biocrusted spaces.At the same time,soil quality in the dead shrub patches was higher than that in the inter-patch spaces.Therefore,it seems that the overall better soil conditions in the dead patches overcome the scarcity of soil-water,supporting increased herbaceous produc-tivity.For explaining the discrepancy between herbaceous vegetation and soil-water,we formulated a conceptual framework,which highlights the key factors that regulate soil-water dynamics in this dryland ecosystem.We demonstrate that herbaceous vegetation is facilitated in the dead shrub patches by a legacy effect that takes place long after the shrubs have died.The dead shrub patches encompass a unique form of ecosystem engineering.The study high-lights the complex and unpredicted impacts of prolonged droughts on dryland ecosystems.     

基于群落类型的寒区旱区物候特征及其对气候因子的响应——以2000-2019年柴达木盆地为例

植被物候反映了植被对环境的适应策略,物候研究对理解植被的生长机制及其对生态因子的响应有重要意义.以柴达木盆地植被为对象,基于2000-2019年NDVI数据,采用双逻辑函数法和STL时序分解算法,从区域和群落层面研究了物候的静态(空间异质性)、动态(时空变化)及其对气候的响应.结果表明:①柴达木盆地植被生长季始期(SO...     

Water resource formation and conversion and water security in arid region of Northwest China

Climate change and water resource issues are global problems of common concern to the international community, and they are major bottlenecks affecting the eco-environment and sustainable socio-economic development in the arid region of Northwest China. On the basis of results from previous studies, this paper points out that the unique landscape of Northwest China increases the complexity and uncertainty of the climate system. This paper analyzes the key constraints on socio-economic development and ecological security in the region, discusses the impact of climate change on water resources in Northwest China, identifies common themes and the main problems present in research on climate change and water resources in the arid northwest region, and finally, based on the importance and urgency of conducting research on the region’s water resources, proposes scientific problems that need to be addressed: first, the impact of climate change on the formation, conversion and future trends of water resources in the region; second, bidirectional coupling of high-resolution regional climate models and water cycle models of arid region land surface patterns; third, the impact of climate change and human activities on water resources of the arid northwest region. Through consideration and discussion of the above, this paper seeks to further clarify specific areas of research on pressing issues related to climate change and water resources in Northwest China, so as to establish a solid scientific basis for significantly enhancing our ability to respond to climate change and water shortages.     

Natural and human dimensions of environmental change in the proximal reaches of Botswana's Okavango Delta

Though wetlands are vital for the proper functioning of terrestrial ecosystems and provisioning of a wide range of goods and services, their sustainability is being threatened by inappropriate human resource use practices due to our limited understanding of how these systems operate and lack of appropriately informed interventions. We attempt to address these limitations by using historical CORONA photographs of 1967, Landsat imagery of 1989, 1994 and 2001 and information from the literature to investigate the role of natural and human factors in influencing the direction of environmental change in the proximal reaches of Botswana's Okavango Delta. Results of this investigation point to fragmentation of natural habitats, localised degradation of areas close to perennial water supplies, significant increase in woody cover, significant decrease in open grassland, increase in scrub and shrubs, deterioration in the quality of grazing and depletion of specific woody species. With the direction of change pointing to persistent decrease in the environment's supporting potentials, there is urgent need to adopt intervention strategies potentially capable of enhancing sustainable utilisation of natural resources in this sub-region.     

西北干旱区水资源问题研究思考

 气候变化与水资源问题是各国政府部门、学术界和社会公众普遍关注的焦点,也是西北干旱区实现跨越式发展的重要瓶颈之一。在分析前人研究成果基础之上,指出制约西北干旱区社会经济发展和生态安全的关键因素和气候变化对西北干旱区水资源的影响;进而分析西北干旱区气候变化与水资源研究中的热点和难点问题;最后基于西北干旱区水资源研究的重要性和迫切性提出目前亟待解决的研究任务与核心内容,主要包括3个方面：(1)气候变化对西北干旱区水资源形成、转化及未来趋势的影响;(2)气候变化对西北干旱区水循环过程的影响;(3)气候变化对西北干旱区水资源安全的影响。     

黄河源区气候—植被—水文协同演变及成因辨析

全球变化下黄河源区水文过程的演变影响流域生态系统的水源涵养功能,流域植被改变也影响水循环。本文基于气候、植被信息和VIP分布式生态水文模型,开展黄河源区水碳循环要素变化的集成模拟,分析了气候—植被—水文要素的协同演变机制。结果表明,2000年以来黄河源区气候呈暖湿化趋势;植被绿度明显提高,2010—2019年比2000—2009年平均增加了4.5%;生长季延长了至少10 d;植被生产力（GPP）显著上升,倾向率为4.57 gC m^-2 a^-1;植被恢复措施对GPP变化的贡献约为23%,气候变化和大气CO₂升高的施肥效应的贡献为77%。源区植被蒸散量（ET）呈增加趋势,倾向率为2.54 mm a^-1,水分利用效率（WUE）亦提高,平均相对上升率为5.1% a^-1。GPP、ET和WUE年总量及其变化率在海拔4200 m以下随高度上升而减小,之后变化趋缓。源区植被绿度和径流系数与当年和前一年降水呈显著正相关,反映降水蓄存于植物根层土壤的遗留效应。蒸散增强在一定程度上有利于源区地表—大气之间的水分再循环,帮助缓解生态恢复引起的产水能力下降,促进降水—植被—径流之间的良性互馈关系的形成。揭示水文对气候变化和植被恢复的响应和互馈机制,可为生态恢复措施对源区水源涵养功能的影响及效应的定量评估提供科学依据。