Start of vegetation growing season on the Tibetan Plateau inferred from multiple methods based on GIMMS and SPOT NDVI data

In this study, we have used four methods to investigate the start of the growing season (SGS) on the Tibetan Plateau (TP) from 1982 to 2012, using Normalized Difference Vegetation Index (NDVI) data obtained from Global Inventory Modeling and Mapping Studies (GIMSS, 1982-2006) and SPOT VEGETATION (SPOT-VGT, 1999-2012). SGS values estimated using the four methods show similar spatial patterns along latitudinal or altitudinal gradients, but with significant variations in the SGS dates. The largest discrepancies are mainly found in the regions with the highest or the lowest vegetation coverage. Between 1982 and 1998, the SGS values derived from the four methods all display an advancing trend, however, according to the more recent SPOT VGT data (1999-2012), there is no continuously advancing trend of SGS on the TP. Analysis of the correlation between the SGS values derived from GIMMS and SPOT between 1999 and 2006 demonstrates consistency in the tendency with regard both to the data sources and to the four analysis methods used. Compared with other methods, the greatest consistency between the in situ data and the SGS values retrieved is obtained with Method 3 (Threshold of NDVI ratio). To avoid error, in a vast region with diverse vegetation types and physical environments, it is critical to know the seasonal change characteristics of the different vegetation types, particularly in areas with sparse grassland or evergreen forest.     

Multifunctionality and Thresholds of Alpine Grassland on the Tibetan Plateau

Ecosystems can simultaneously provide multiple functions and services. Knowledge on the combinations of such multi-dimensional functions is critical for accurately assessing the carrying capacity and implementing sustainable management. However, accurately quantify the multifunctionality of ecosystems remains challenging due to the dependence and close association among individual functions. Here, we quantified spatial patterns in the multifunctionality of alpine grassland on the Tibetan Plateau by integrating four important individual functions based on data collected from a field survey and remote sensing NDVI. After mapping the spatial pattern of multifunctionality, we extracted multifunctionality values across four types of grassland along the northern Tibet Plateau transect. Effects of climate and grazing intensity on the multifunctionality were differentiated. Our results showed that the highest values of multifunctionality occurred in the alpine meadow. Low values of multifunctionality were comparable in different types of grassland. Annual precipitation explained the large variation of multifunctionality across the different types of grassland in the transect, which showed a significantly positive effect on the multifunctionality. Grazing intensity further explained the rest of the variation in the multifunctionality (residuals), which showed a shift from neutral or positive to negative effects on multifunctionality across the different types of grassland. The consistently rapid declines of belowground biomass, SOC, and species richness resulted in the collapse of the multifunctionality as bare ground cover amounted to 75%, which corresponded to a multifunctionality value of 0.233. Our results are the first to show the spatial pattern of grassland multifunctionality. The rapid decline of the multifunctionality suggests that a collapse in the multifunctionality can occur after the vegetation cover decreases to 25%, which is also accompanied by rapid losses of species and other individual functions. Our results are expected to provide evidence and direction for the sustainable development of alpine grassland and restoration management.     

Crop cover reconstruction and its effects on sediment retention in the Tibetan Plateau for 1900–2000

Geographically explicit historical land use and land cover datasets are increasingly required in studies of climatic and ecological effects of human activities. In this study, using historical population data as a proxy, the provincial cropland areas of Qinghai province and the Tibet Autonomous Region (TAR) for 1900, 1930, and 1950 were estimated. The cropland areas of Qinghai and the TAR for 1980 and 2000 were obtained from published statistical data with revisions. Using a land suitability for cultivation model, the provincial cropland areas for the 20th century were converted into crop cover datasets with a resolution of 1 × 1 km. Finally, changes of sediment retention due to crop cover change were assessed using the sediment delivery ratio module of the Integrated Valuation of Ecosystem Services and Trade-offs (In- VEST) model (version 3.3.1). There were two main results. (1) For 1950–1980 the fractional cropland area increased from 0.32% to 0.48% and land use clearly intensified in the Tibetan Plateau (TP), especially in the Yellow River–Huangshui River Valley (YHRV) and the midstream of the Yarlung Zangbo River and its two tributaries valley (YRTT). For other periods of the 20th century, stability was the main trend. (2) For 1950–1980, sediment export increased rapidly in the Minhe autonomous county of the YHRV, and in the Nianchu River and Lhasa River basins of the YRTT, which means that sediment retention clearly decreased in these regions over this period. The results of this assessment provide scientific support for conservation planning, development planning, or restoration activities.     

史前人类在青藏高原的定居与动物资源利用

定居是人类从高度移动的游猎生活发展到全年固定于一处居住的漫长过程。定居的发生和发展对人类社会的生产方式、技术演化和文明起源具有深远影响,而定居的产生受到气候变化、人口增长、资源压力、技术革新等多种因素影响。青藏高原是研究人类适应和定居高寒缺氧极端环境的理想区域,对史前人类在青藏高原的定居过程关注较多亦争议颇多。通过梳理已发表的考古学、地理学、遗传学等相关学科文献,发现目前对于史前人类定居青藏高原的研究,侧重于讨论低海拔人群或者农作物扩散的影响,对动物资源在这一过程中的作用则关注较少,定居高原的年代和驱动机制仍存在争议。遗址使用的季节性分析,是判断古人是否全年定居的关键。本文总结了如何利用青藏高原鱼类、鸟类和哺乳类等动物遗存因地制宜进行遗址季节性分析以及建立高原遗址动物资源利用时间表的方法。本文认为,开展史前人类在青藏高原定居与动物资源利用研究,首先,应全面建立和完善青藏高原现生动物骨骼形态、全基因组和蛋白质组的数据库,为考古遗址动物遗存物种鉴定提供基础;其次,在物种鉴定的基础上,研究人—动物—环境之间的关系;最后,评估人类在遗址活动的季节性以及动物资源在人类定居青藏高原过程中的作用。     

高原湖泊中萝卜螺属壳体研究现状及展望

湖泊的古水文及古水化学重建是湖泊研究领域最具挑战性的工作之一。在湖泊、河湖相及高湖面沉积物中,萝卜螺属壳体化石广泛分布;而且现生萝卜螺属亦广泛地分布于全球的湖泊及河流。这些生物碳酸盐(文石)壳体成为一种潜在的和高分辨率的环境信息记录载体。近年来,萝卜螺属的生境及其壳体的稳定碳氧同位素和元素已经逐步被用于了解青藏高原及其他地区的古水文、古水化学和古气候的信息。然而,在萝卜螺属壳体如何记录其宿生水体的古水文、古水化学等信息,以及如何基于萝卜螺属壳体化石重建古环境等方面,仍有许多科学问题有待探索。本文在前人研究的基础上,侧重在作为环境信息载体的萝卜螺属的分类体系、生境研究及其应用和壳体指标(δ¹³C_shell,δ¹⁸O_shell,⁸⁷Sr/⁸⁶Sr,Sr/Ca和Mg/Ca)特征及其在环境重建中的应用等方面进行总结和展望。     

青藏高原植被覆盖变化及其与气候变化的关系

近几十年来,全球气候变化对青藏高原植被覆盖产生了重要影响。基于青藏高原1981—2005年遥感影像及同期气象数据,结合生态学模型,分析了青藏高原植被覆盖度变化趋势及其与气候变化的关系。结果显示,25 a间,青藏高原温度升高、降水量增加,植被覆盖度呈"整体升高、局部退化"趋势;地表植被改善区主要位于植被低覆盖区,退化区主要位于高覆盖区;从不同植被类型看,除针叶林、阔叶林受采伐影响覆盖度下降外,其他植被覆盖度均不同程度的上升;植被覆盖度变化与同期降水量变化、温度变化均呈正相关,且具有明显的区域差异。     

湖南茶陵县域生态空间网络稳定性识别与重构策略

县域是国土空间规划与管理的基本单元,针对县域生态空间网络的识别与重构是空间优化的重要途径,对生态保护红线划定具有积极作用,但现有空间网络分析的方法论明显滞后。以典型丘陵山区县湖南茶陵县生态空间网络构建和识别为基础,运用鲁棒性分析法表达生态系统受特定干扰后的变化特征,进行节点重要度评价和网络稳定性分析。结果表明：节点重要度和数量是判定网络稳定性的关键因子,该类节点数量占5%左右且多位于茶陵县域罗霄山片区,对应景观类型多为林地,其次为水域和草地、园地等生态用地;生态空间网络稳定性变化值均表现出与节点数量的高度一致,网络节点失效比率高于92%时将完全瘫痪,低于20%可恢复稳定;以人类活动干扰为主的蓄意破坏情景中连通鲁棒性变化更为敏感,对网络连通性影响较大;依据重要节点分布及稳定性判断结果,结合生态保护红线划定方案,提出区域生态保护的差异化管理和生态空间网络重构建议。研究既为县域生态空间规划和生态保护红线管控提供有效支撑,也为类似区域生态空间网络研究提供了案例借鉴。     

2009-2015年国际青藏高原研究文献计量分析——基于SCIE和ESI数据

青藏高原及其周边地区以独特的自然地理环境和复杂的地质构造,及其对全球环境和气候变化不可忽视的影响,长期以来一直受到国际科学家的关注。本文以SCIE和ESI数据库为数据源,检索2009-2015年间上述数据库报道的青藏高原及其周边地区研究文献及其引用情况,通过文献计量方法,采用多种分析工具,从多个角度对青藏高原及其周边地区研究现状与进展情况进行分析,在此基础上总结近年来国际青藏高原领域的研究态势,主要结论为：整体上近年来国际青藏高原领域研究规模和学术影响力呈现良好发展态势;研究实力上,中国、印度、美国仍稳居国家论文产出前三位,但青藏高原周边国家如巴基斯坦、尼泊尔发展较快,在机构层面上中国机构的整体优势逐渐扩大。中国的青藏高原研究呈现出量、质齐升的发展态势;青藏高原的发文期刊仍以地学、环境类期刊为主,高被引论文主要发表在高质量的综合类期刊上。青藏高原的研究学科持续完备,研究内容地域特色明显,研究主题包括青藏高原的隆升机制、高原各个圈层对全球气候变化的影响、高寒生态系统的生物多样性及对全球变暖的响应等。今后,中国青藏高原研究应着力聚焦前沿科学问题,促进多学科交叉融合,提升协同化集成化自主科研创新能力,产出具有国际影响力的重大科学成果,为“一带一路”战略实施和区域生态环境管理提供科技支撑。     

青藏高原东北部与南部地区树木径向生长对气候要素的响应——以祁丰和林周树轮为例

了解树木径向生长对气候响应的区域特征是模拟或预测未来全球变化如何对森林生态系统产生影响的基础。对青藏高原东北部(祁丰)干旱气候条件下与南部(林周)高寒半干旱气候条件下的两条标准化年表分析发现,两年表敏感度均较高,样芯间一致性均较强,为分析树木径向生长对气候要素的响应关系提供了保障。对祁丰和林周树轮宽度序列与其附近酒泉(1951-2009年)和当雄(1963-2009年)气象站上年5月到当年9月的气候因子(月平均气温、月最高气温、月平均最低温和月降水量)进行相关和响应分析发现,祁丰和林周树木的径向生长与当年5-6月平均气温存在负相关关系,相关系数分别为-0.360和-0.466;而与当年5-6月降水量显著正相关,相关系数分别为0.499和0.623。祁丰和林周树轮宽度序列与帕尔默干旱指数(PDSI,1951-2005年)的格网数据在每个月份均呈正相关关系,与5-6月的相关值分别为0.581和0.719。上年7月到当年6月的降水量与祁丰(r=0.529)和林周(r=0.667)树轮宽度序列的相关值也较高,推断干旱状况是限制高原东北部与南部树木径向生长的主要因素。     

基于SSA和MGF的海面变化长期预测及对比

海面变化预测受到建模思路、方法选择、数据长度及数据质量等因素的影响,导致了海面变化预测的不确定性。本文以国内6个验潮站自20世纪50年代以来的月平均潮位序列为基础,采用奇异谱分析(SSA)与均值生成函数(MGF)模型相结合的方案,以各站位最初20余年数据为基础建立预测模型,以后续年份的实测数据进行了多方案对比验证及检验。预测试验显示MGF模型具有较高的预测精度,并表现出较好的长期预测的稳定性特点。以SSA去噪序列为基础,应用MGF模型预测了各站位至2050年的月尺度海面值,年均值计算结果表明至2050年海面波动上升的幅度不超过20cm,海面变化速率同样表现出阶段性和波动性。与前人相关研究成果对比表明,本文所采用的SSA与MGF相结合的预测结果具有可比性,在方法原理和验证结果上看具有较好的长期预测潜力。