晚更新世晚期以来昆仑山垭口区的植被与环境

昆仑山垭口区小南川剖面和雪水河热水剖面的孢粉分析揭示了该区４４０００ａＢ．Ｐ．以来的植被演替和气候变化。４００００ａＢ．Ｐ．前,推测昆仑山垭口区为典型的灌木荒漠植被,气候极端干燥。４００００－３００００ａＢ．Ｐ．,气候稍有好转。３００００－２４０００ａＢ．Ｐ．为草原荒漠,降水增加。２４０００－１８０００ａＢ．Ｐ．为末次冰期极盛期,气候干冷。１８０００－１３０００ａＢ．Ｐ．气候凉偏干。１３０００－８０００ａＢ．Ｐ．气候凉干。８０００－６０００ａＢ．Ｐ．为全新世温暖期,但由于植被的滞后现象,本区仍为草原荒漠景观。６０００－５０００ａＢ．Ｐ．,本区可能也存在着中全新世的降温事件。５０００－３０００ａＢ．Ｐ．在全新世大暖期的影响下,小南川附近的植被演变成温性草原植被,并有人类的放牧活动。３０００ａＢ．Ｐ．以后,气候变凉,草原迅速地演变为灌木和小乔木荒漠植被,其中３０００－１０００ａＢ．Ｐ．为凉干时期,１０００ａＢ．Ｐ．以后,可能有过一段凉湿时期。     

根据孢粉分析论青藏高原西部和北部全新世环境变化

通过对青藏高原西部班公湖钻孔和北部中昆仑山３个湖相剖面的孢粉研究,揭示青藏高原西部和北部地区全新世１万年期间植被的演替和气候变化,西部在全新世早期９９００－７８００ｙｒ．Ｂ．Ｐ．植被由荒漠转为草原,气候好转;中期７８００－３５００ｙｒ．Ｂ．Ｐ．,草原发展,气候较适宜,以７２００－６３００ｙｒ．Ｂ．Ｐ．为高温湿期,５５００ｙｒ．Ｂ．Ｐ．和３５００ｙｒ．Ｂ．Ｐ．出现干旱,晚期从３５００ｙｒ．Ｂ．Ｐ．至今植被为荒漠,气候干旱,其中７００ｙｒ．Ｂ．Ｐ．气候恶化。北部地区全新世时期为荒漠植被,当气候温湿时,蒿和禾本科,莎草科成份增加,藜科减少,气候干旱时则相反,北部全新世的气候分期和干湿波动与西部相近,两地在晚期气候朝干旱化发展。     

东北全新世乔木种类演化的区域差异及其迁移问题

根据花粉等时线图和代表性剖面花焰资料,总结了东北全新世主要乔木在再现和发展的地区差异。三江平原和小兴安岭地区的栎属与松属的出现和发展分别比长白山地区推迟１－－２千多上时间上的差别说明它们可能有从南向北的迁移过程。不同乔木种类迁移的速率也不一样。初步估计的几种乔木迁移速率为,栎２５０～５９０ｍ／ａ,松属１５０－５８０ｍ／ａ,胡桃属２００－８１０ｍ／ａ。这种差异可能主要与种子大小、河流和地形等因素有联     

我国东北全新世花粉分布图及其分析

根据６５个地点化石花粉分析资料,编制了我国东北全新世每隔每千年时间片断的花粉百分值图和花粉等时线图,并进行初步分析,花粉图展示了东北地区植被演化的主要特征。桦树在全新世初期遍布从三江平原到辽东半岛南端的东北东部地区,在森林中占据色对优势地位,榆属和栎属等阔叶乔枯木要在早全新世的大部分时间内是东部森林中的主要种类;在大约５ｋａＢＰ以后,松属在东北现在的森林地区开始增加,云,冷杉属也表现出较明显扩大,     

黄土高原西部4万多年以来植被与环境变化的孢粉记录

采集甘肃静宁、定西、秦安等地晚更新世晚期以来几个黄土剖面的孢粉样品,分别以晚更新世每个样品分辨率200—300年,全新世20—200年,揭示了黄土高原西部4万多年以来古植被曾经历过草原、森林草原(或疏林草原)、针叶林以及荒漠草原或荒漠几种植被的多次快速变化。在44.2—11kaBP期间,静宁地区植被主要表现为森林和草原成分的相互消长,其中44—29kaBP期间(MIS3)气候以湿润为主,发育针叶林,温度低于现在;23kaBP之后,气候冷干,以稀疏草原为主,在末次盛冰期植被甚至演化为荒漠草原。全新世大部分时间内是以草原或森林草原(或疏林草原)植被为主。在全新世中期,约7.6—5.8kaBP有近1700年时间发育有森林植被,在这个时期当地自然植被覆盖度较高,而草原或疏林草原发育时期植被往往较稀疏,反映气候相对干冷。根据出现的不同类型植物的孢粉浓度及其生态环境特性,研究区早、中全新世,约8.8—5.8kaBP沉积环境较湿润;自3.8kaBP以后气候环境总的变化趋势是逐渐变干,植被开始向草原荒漠化演变。然而,研究区整个全新世气候环境存在多次干湿交替现象,据孢粉记录,其中可能存在11次气候干寒事件。     

河北北部、内蒙古东部森林-草原交错带生物多样性研究

河北北部、内蒙古东部森林－草原交错带富于高的生物多样性。在森林－草原交错带森林草甸区森林斑块的数量最多,其次为森林带,再次为森林－草原交错带草甸草原区,草原带没有森林斑块。植物群落的α多样性在森林群落和草原群落表现不同,森林群落从森林带到草原带依次减低;草原群落则表现出在森林－草原交错带植物多样性高,特别是在森林草甸区最明显,在森林－草原交错带β多样性指数较高,表现在β多样性指数在森林－草原交错带     

中国森林C汇功能基本估计

根据森林资源消长状况和未来变化趋势,对中国森林因Ｃ的现状和潜力进行了估计和预测．结果表明,中国森林目前Ｃ积累高于Ｃ释放,年平均净固Ｃ量为０．８６２７×１０８ｔ·ａ－１,在未来２０年内中国森林净固Ｃ能力约增加７７３×１０４ｔ·ａ－１．到２０００年,中国森林固Ｃ能力将达到１．４６９７×１０８ｔ·ａ－１．     

鄂尔多斯高原生态过渡带的判定及生物群区特征

本文用Holdridge生命地带方法对鄂尔多斯高原的生物群区进行了分类研究,研制了用于生态过渡带判定的计算机模型,模拟结果与实际情况基本吻合。鄂尔多斯高原的生物群区可分为草原、荒漠灌丛和荒漠3大类,草原群区以本氏针茅(Stipa bungeana)群落为主,荒漠灌丛群区以冷蒿(Artemisia frigida),狭叶锦鸡儿(Caragana stenophylla)群落为主,荒漠群区以红砂(Reaumuria soongorica)群落为主。鄂尔多斯高原的地带性植被在传统上分为典型草原、荒漠草原和草原化荒漠3部分,在典型草原的边界划分上,传统划分与本文结果一致。而在荒漠草原和草原化荒漠的边界方面,模拟结果与传统划分有一定的差异。荒漠灌丛和荒漠草原以及荒漠和草原化荒漠在生物群落特征上具有一定的相似性,荒漠灌丛和荒漠在生态特征上较荒漠草原和草原化荒漠更为旱化,在地理位置上更为靠西部。该计算机模型结合了地理空间分析,能准确地确定生态过渡带的位置和宽度,为研究鄂尔多斯高原生态过渡带的特征提供了较可靠的技术手段。     

中国中全新世植被带迁移的气候动力学机制探讨

地球轨道参数驱动的太阳辐射变化造成了中全新世北半球大陆夏季的普遍增温,但中低纬度的冬季温度低于现代。古气候模型和古植被模型在这个动力驱动基础上,对东亚季风区的票据均反映了北半球中低纬度的冬季温度低于现代,由此主要受冬季温度控制的中纬度森林植被向南迁移。然而,根据花粉资料重建的中全民植被表明,中国东部森林植被带向北迁移,其中常绿阔叶林北移３００ｋｍ,落叶阔叶林北移５００～６００ｋｍ。根据古植被类比研     

气候变暖与荒漠-草原过渡带植物动态响应灰色分析--以美国新墨西哥州Sevilleta生态过渡带为例

在当前全球气候变暖的形势下,地表生态系统表现出不同的响应。干旱-半干旱地区的生态过渡带的生物反应更为敏感。美国新墨西哥州中部的荒漠-草原生态过渡带是监测全球气候变化和人类活动对生物影响的重要区域之一。本文以Sevilleta荒漠．草原生态过渡带为例,运用灰色系统分析方法．研究在当前全球气候变暖的条件下,1989～1998年10年间该生态过渡带的两种共存的植物优势种(Bouteloua eripoda)和(Bouteloua grncilis)历年的种群密度、组合形式和变化趋势,分析引起这些变化的主要气候因子。结果表明,Sevilleta生态过渡带中来自荒漠草原的优势物种Bouteloua eripoda的密度有上升的趋势,来自大草原的优势物种Bouteloua gracilis的密度有下降的趋势,它们的密度比大于1且有上升的趋势;在影响种群密度变化的降水、最高温度、最低温度、湿度的4个气候因子中,温度因子起着重要的作用。由此可以认为,随着气候的变暖,本区来自荒漠地区的优势植物种在荒漠-草原群落过渡带中将逐渐处于强优势地位,生态过渡带将有可能被荒漠草原所替代。     

黑龙江西部生态脆弱带景观格局研究

运用景观生态学格局的分析方法,对黑龙江西部生态脆弱带典型的土地景观进行了分析,并对各种分析方法进行了对比,探讨了各种景观类型的关系,并对人类活动的影响与景观之间的关系进行了分析。     

样地尺度现代表土花粉与植物群落的定量关系

建立现代植被与表土花粉的精确关系,是基于孢粉记录定量重建古植被与古气候的基础与关键.截止目前,植物群落样方记录较少参与到现代植被与花粉的统计分析中,限制了其精确关系的定量表达.本文通过中国东北样带的森林、草甸草原、典型草原和荒漠草原33个表土样品分析及植被样方调查,基于Bray-Curtis相异系数,研究了东北样带现代...     

Pollen-based biome reconstruction for southern Europe and Africa 18,000 yr bp

Pollen data from 18,000 ¹⁴C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.     

Numerical Characteristics of Pollen Assemblages of Surface Samples from the West Kunlun Mountains

A total of 31 suface sediment samples were collected from West Kunlun Mountain in south Xinjiang Autonomous Region in northwest China. These samples are from seven types of vegetation: Picea schrenkiana Fisch. et Mey. forest, Sabina Spach. woodland, sub-alpine steppe, alpine meadow, desert vegetion, cushion-vegetation and vegetation adjancent to glaciers. Pollen percentages and pollen concentrations were calculated in all samples. The dominant pollen types in the region are Chenopodiaceae, Artemisia, Picea, Ephedra, Gramineae, Cyperaceae, Rosaceae, Leguminosae, Compositae etc. In order to reveal the relationship between pollen composition and the vegetation type from which the soil sample was collected, principal component analysis and group average cluster analysis were employed on the pollen data. The results revealed that the major vegetation types in this region could be distinguished by pollen composition: a. Samples from desert vegetation were dominated by pollen of Chenopodiaceae (about 60195%). The percentages of all other pollen types were low. b. Picea forest samples were rich in Picea pollen (about 20%) Sabina forest had more Sabina pollen grains than other vegetation types (about 5%, others <1%). Pollen percentages of Artemisia, Chenopodiaceae and Ephedra were comparatively higher (each about 20%) in these samples from the two types of vegetations. C. Pollen percentages of Artemisia, Cyperaceae, Gramineae and Chenopodiaceae were high in both sub-alpine steppe and alpine meadow. But steppe containal more Artemisia and Chenopodiaceae (steppe 33.75% and 32.30%, meadow 15.57% and 19.48% in average), less Cyperaceae and Gramineae (steppe 2.58% and 7.60%, meadow 22.35% and 12.93% in average) than meadow. d. Samples from cushion-vegetation and vegetation adjacent to glaciers were mainly composed of pollen grains transported from other sites. It was not easy to distinguish them from other vegetation types. Principal component analysis and cluster analysis distinguish samples from Picea forest, Sabina woodland, sub-alpine steppe, alpine meadow and desert vegetation. Therefore we think it will be possible to apply the module to reconstruct past vegetation in this region and other similar regions. Regression analysis was also applied to reveal the relationships between pollen and plant percentages of Artemisia, Chenopodiaceae, Cyperaceae and Gramineae. The results indicated that a linear relationship existed between pollen and plant percentages for Artemisia, Chenopodiaceae and Cyperaeeae.     

内蒙古东南部季风气候尾闾区全新世降水量时空差异性的孢粉学证据

内蒙古高原东南部森林草原过渡带位于中国东部季风气候尾闾区,是全球变化研究的关键区域.这一地区降水量存在着明显的东南至西北(SE-NW)梯度.在现代植被和表土花粉分析的基础上,建立了内蒙古高原东南缘森林草原过渡带孢粉-降水量转换函数.将研究区森林草原过渡带内3个湖泊沉积剖面的孢粉分析结果代入转换函数,定量恢复了这一地区全新世降水量的变化过程.结果表明:3个剖面全新世以来降水量变化的过程存在明显的差异,北部的好鲁库剖面在1 100 a BP以前一直呈减弱的趋势,而南部的碌轴湾剖面和小牛场剖面降水量在分别在7 800-6 200 a BP和7 200-5 000 a BP出现降水量的峰值,作者推断这种时空差异性与西南季风的影响、地形条件的差异有关.     

Present-day and mid-Holocene biomes reconstructed from pollen and plant macrofossil data from the former Soviet Union and Mongolia

Fossil pollen data supplemented by tree macrofossil records were used to reconstruct the vegetation of the Former Soviet Union and Mongolia at 6000 years. Pollen spectra were assigned to biomes using the plant-functional-type method developed by Prentice et al . (1996). Surface pollen data and a modern vegetation map provided a test of the method. This is the first time such a broad-scale vegetation reconstruction for the greater part of northern Eurasia has been attempted with objective techniques. The new results confirm previous regional palaeoenvironmental studies of the mid-Holocene while providing a comprehensive synopsis and firmer conclusions. West of the Ural Mountains temperate deciduous forest extended both northward and southward from its modern range. The northern limits of cool mixed and cool conifer forests were also further north than present. Taiga was reduced in European Russia, but was extended into Yakutia where now there is cold deciduous forest. The northern limit of taiga was extended (as shown by increased Picea pollen percentages, and by tree macrofossil records north of the present-day forest limit) but tundra was still present in north-eastern Siberia. The boundary between forest and steppe in the continental interior did not shift substantially, and dry conditions similar to present existed in western Mongolia and north of the Aral Sea.     

Holocene carbon dynamics at the forest–steppe ecotone of southern Siberia

The forest–steppe ecotone in southern Siberia is highly sensitive to climate change; global warming is expected to push the ecotone northwards, at the same time resulting in degradation of the underlying permafrost. To gain a deeper understanding of long‐term forest–steppe carbon dynamics, we use a highly resolved, multiproxy, palaeolimnological approach, based on sediment records from Lake Baikal. We reconstruct proxies that are relevant to understanding carbon dynamics including carbon mass accumulation rates (CMAR; g C m^?2 yr^?1) and isotope composition of organic matter (δ¹³C_TOC). Forest–steppe dynamics were reconstructed using pollen, and diatom records provided measures of primary production from near‐ and off‐shore communities. We used a generalized additive model (GAM) to identify significant change points in temporal series, and by applying generalized linear least‐squares regression modelling to components of the multiproxy data, we address (1) What factors influence carbon dynamics during early Holocene warming and late Holocene cooling? (2) How did carbon dynamics respond to abrupt sub‐Milankovitch scale events? and (3) What is the Holocene carbon storage budget for Lake Baikal. CMAR values range between 2.8 and 12.5 g C m^?2 yr^?1. Peak burial rates (and greatest variability) occurred during the early Holocene, associated with melting permafrost and retreating glaciers, while lowest burial rates occurred during the neoglacial. Significant shifts in carbon dynamics at 10.3, 4.1 and 2.8 kyr bp provide compelling evidence for the sensitivity of the region to sub‐Milankovitch drivers of climate change. We estimate that 1.03 Pg C was buried in Lake Baikal sediments during the Holocene, almost one‐quarter of which was buried during the early Holocene alone. Combined, our results highlight the importance of understanding the close linkages between carbon cycling and hydrological processes, not just temperatures, in southern Siberian environments.     

Biome reconstruction from pollen and plant macrofossil data for Africa and the Arabian peninsula at 0 and 6000 years

Biome reconstruction from pollen and plant macrofossil data provides an objective method to reconstruct past vegetation. Biomes for Africa and the Arabian peninsula have been mapped for 6000 years bp and provide a new standard for the evaluation of simulated palaeovegetation distributions. A test using modern pollen data shows the robustness of the biomization method, which is able to predict the major vegetation types with a high confidence level. The application of the procedure to the 6000 years data set (pollen and plant macrofossil analyses) shows systematic differences from the present that are consistent with the numerous previous regional and continental interpretations, while providing a more extensive and more objective basis for such interpretations. Madagascar, eastern, southern and central Africa show only minor changes in terms of biomes, compared to present. Major changes in biome distributions occur north of 15°N, with steppe in many low-elevation sites that are now desert, and temperate xerophytic woods/scrub and warm mixed forest in the Saharan mountains. These shifts in biome distributions imply significant changes in climate, especially precipitation, between 6000 years and present, reflecting a change in monsoon extent combined with a southward expansion of Mediterranean influence.     

Pollen-based biome reconstructions for China at 0 and 6000 years

Biomization provides an objective and robust method of assigning pollen spectra to biomes so that pollen data can be mapped and compared directly with the output of biomgeographic models. We have tested the applicability of this procedure, originally developed for Europe, to assign modern surface samples from China to biomes. The procedure successfully delineated the major vegetation types of China. When the same procedure was applied to fossil pollen samples for 6000 years ago, the reconstructions showed systematic differences from present, consistent with previous interpretations of vegetation changes since the mid-Holocene. In eastern China, the forest zones were systematically shifted northwards, such that cool mixed forests displaced taiga in northeastern China, while broad-leaved evergreen forest extended c. 300 km and temperate deciduous forestc. 500–600 km beyond their present northern limits. In northwestern China, the area of desert and steppe vegetation was reduced compared to present. On the Tibetan Plateau, forest vegetation extended to higher elevations than today and the area of tundra was reduced. These shifts in biome distributions imply significant changes in climate since 6000 years ago that can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Asian monsoon.     

Modern pollen samples from alpine vegetation on the Tibetan Plateau

• 1 A set of 316 modern surface pollen samples, sampling all the alpine vegetation types that occur on the Tibetan Plateau, has been compiled and analysed. Between 82 and 92% of the pollen present in these samples is derived from only 28 major taxa. These 28 taxa include examples of both tree (AP) and herb (NAP) pollen types.
• 2 Most of the modern surface pollen samples accurately reflect the composition of the modern vegetation in the sampling region. However, airborne dust‐trap pollen samples do not provide a reliable assessment of the modern vegetation. Dust‐trap samples contain much higher percentages of tree pollen than non‐dust‐trap samples, and many of the taxa present are exotic. In the extremely windy environments of the Tibetan Plateau, contamination of dust‐trap samples by long‐distance transport of exotic pollen is a serious problem.
• 3 The most characteristic vegetation types present on the Tibetan Plateau are alpine meadows, steppe and desert. Non‐arboreal pollen (NAP) therefore dominates the pollen samples in most regions. Percentages of arboreal pollen (AP) are high in samples from the southern and eastern Tibetan Plateau, where alpine forests are an important component of the vegetation. The relative importance of forest and non‐forest vegetation across the Plateau clearly follows climatic gradients: forests occur on the southern and eastern margins of the Plateau, supported by the penetration of moisture‐bearing airmasses associated with the Indian and Pacific summer monsoons; open, treeless vegetation is dominant in the interior and northern margins of the Plateau, far from these moisture sources.
• 4 The different types of non‐forest vegetation are characterized by different modern pollen assemblages. Thus, alpine deserts are characterized by high percentages of Chenopodiaceae and Artemisia, with Ephedra and Nitraria. Alpine meadows are characterized by high percentages of Cyperaceae and Artemisia, with Ranunculaceae and Polygonaceae. Alpine steppe is characterized by high abundances of Artemisia, with Compositae, Cruciferae and Chenopodiaceae. Although Artemisia is a common component of all non‐forest vegetation types on the Tibetan Plateau, the presence of other taxa makes it possible to discriminate between the different vegetation types.
• 5 The good agreement between modern vegetation and modern surface pollen samples across the Tibetan Plateau provides a measure of the reliability of using pollen data to reconstruct past vegetation patterns in non‐forested areas.