Relationships between modern pollen and vegetation and climate on the eastern Tibetan Plateau

The Tibetan Plateau ecosystem is fragile and sensitive to climate change. Understanding the relationships between modern pollen and the vegetation and climate of the region is critical for the evaluation of ecological processes.Here, we explore modern pollen assemblages of typical land-cover types at a large spatial scale by analyzing 36surface samples from the southeastern Tibetan Plateau, supplemented by typical desert, desert-steppe, and steppe meadow transition data selected from the Chinese Surface Pollen Database, giving a total of 75 samples. We used redundancy analysis(RDA) to explore the responses of vegetation in the assemblages to regional climate. Our results show that pollen assemblages generally reflect the vegetation composition: assemblages from alpine meadow samples are dominated by Cyperaceae, Asteraceae, Rosaceae, and Polygonaceae;alpine shrublands mainly comprise Fabaceae, Rosaceae, Ericaceae, and Quercus(Q. spinosa);and coniferous forest surface samples mainly comprise Picea, Abies, Pinus, and Betulaceae. Our RDA shows that mean annual precipitation(MAP) is the main meteorological factor affecting the pollen assemblage and vegetation type;MAP positively correlates with percentages of Cyperaceae, Poaceae, Rosaceae, and Asteraceae, and negatively correlates with percentages of Chenopodiaceae, Ephedraceae, Nitraria, and Tamaricaceae. The ratio of Artemisia to Chenopodiaceae is a useful indicator to distinguish temperate desert from other land-cover types on the Tibetan Plateau, while the ratio of Cyperaceae + Asteraceae to Artemisia + Chenopodiaceae can be used to distinguish arid desert from other landcover types, and may provide a useful altitude index for the eastern Tibetan Plateau.

Quantitative contributions of climate change and human activities to vegetation dynamics in the Zoige Plateau from 2001 to 2020

Climate change and human activities such as overgrazing and rapid development of tourism simultaneously affected the vegetation of the Zoige Plateau.However,the spatiotemporal variations of vegetation and the relative contributions of climate change and human activities to these vegetation dynamics remain unclear.Therefore,clarifying how and why the vegetation on the Zoige Plateau changed can provide a scientific basis for the sustainable development of the region.Here,we investigate NDVI trends using the Normalized Difference Vegetation Index(NDVI)as an indicator of vegetation greenness and distinguish the relative effects of climate changes and human activities on vegetation changes by utilizing residual trend analysis and the Geodetector.We find a tendency of vegetation greening from 2001 to 2020,with significant greening accounting for 21.44%of the entire region.However,browning area expanded rapidly after 2011.Warmer temperatures are the primary driver of vegetation changes in the Zoige Plateau.Climatic variations and human activities were responsible for 65.57%and 34.43%of vegetation greening,and 39.14%and 60.86%of vegetation browning,respectively,with browning concentrated along the Yellow,Black and White Rivers.Compared to 2001-2010,the inhibitory effect of human activity and climate fluctuations on vegetation grew dramatically between 2011 and 2020.

STUDY ON VEGETATION AND CLIMATE CHANGES IN BEIJING REGION SINCE LATE PLEISTOCENE

A complex history of the Late Pleistocene vegetation and environmental changes for the northern part of the deciduous forest is revealed in an exceptionally well dated pollen diagram from Dongganchi in Beijing area. In 15?800- 14?700 a B.P., the arbors and aquatic plants were sparse, and the climate was cold and dry. In 14 700-13?400 a B.P., forest growth was limited, it was dominated by conifers, presumably in responded to a cooling climate. Aquatic plants became abundant. During 13?400 to 12?600 a B.P., there was a widespread development of coniferous and broad leaved mixed forest, aquatic plants decreased which corresponded to climate gradually becoming warming and dry. In 12?600-11?400 a B.P., there was alternation of coniferous and broad leaved mixed forest, so were aquatic plants. From 11?400 to 9?600 a B.P., the decreasing of trees and increasing of herbs and shrubs suggested an opening up of the vegetation in responded to cooling, probably corresponded to Younger Dryas from 10?600 to 10?300 a B.P. About 9600-7270 a B.P., the climate changed from cooler and dry to warmer and humid. About 7270-3390 a B.P., the coniferous and the broad leaved mixed forest increased, it was in responding to the “climatic optimum". About 3390-1000 a B.P., climate became cooler and dry. After 1000 a B.P., there was a severe fluctuation, indicating the temperature drop and the environmental deterioration.

STUDIES ON QUATERNARY SPORO-POLLEN ASSEMBLAGE AND PALEOCLIMATE BASED ON BOHAI SEA CORE B_(C-1)

Analysis of 13 spore-pollen assemblage zones reflecting environmental changes since the later middle Pleistocene showed the succession of paleovegetation and the paleogeographic changes in the Bohai Basin and circumjacent area. Paleoclimatic variations here can obviously be divided into 5 cold and 5 warm periods : 2 cold and 1 warm periods in 200 ,000-100, 000 a B . P. (late middle Pleistocene ) 3 cold and 3 warm periods in 100 , 000-12 , 000 a B. P. (late Pleistocene), and 1 warm period since 12 ,000 a B. P. Late Pleistocene climate tended to become colder and colder. The coldest period was in the later stage of late Pleistocene, when the study area was a periglacial zone. The mean annual temperature then was about 10℃ lower than it is now. In the middle stage of late Pleistocene, climate became warm ; the mean annual temperature then was about 3 - 4℃ higher than it is now.By applying principles of climatic stratigraphy, the authors deduced through spore-pollen analysis , that the boundary between

Modern pollen assemblages from surface lake sediments in northwestern China and their importance as indicators of vegetation and climate

The modern pollen assemblages of surface lake sediments and topsoils in northwestern China were studied to understand the relationship of modern pollen data with contemporary vegetation and climate, and the differences between the pollen assemblages of surface lake sediments and topsoils. The results show that Chenopodiaceae and Artemisia are dominant elements in the pollen assemblages of northwestern China. Additionally, Ephedra, Cyperaceae, Asteraceae, Poaceae, Picea, Pinus, and Betula are also important pollen taxa. Both pollen assemblages and principal component analysis indicate that pollen data from surface lake sediments and topsoils can be used to differentiate the main vegetation types of this region(desert, steppe, meadow and forest). However, differences exist between modern pollen assemblages of the two types of sediments due to the different relevant source areas of pollen and degrees of pollen preservation. For example, the larger relevant source area of surface lake sediment results in a higher abundance of Betula in pollen assemblage from surface lake sediment, whereas the tendency to disintegrate thin-walled pollen types in topsoil leads to a higher proportion of resistant pollen, such as Asteraceae. Linear regression analysis indicates that the Artemisia/Chenopodiaceae(A/C) ratio in pollen assemblages of surface lake sediments can be used to indicate humidity changes in the study area. However, the A/C ratio in topsoils should be used carefully. Our results suggest that pollen data from surface lake sediments would be better references for interpreting the fossil pollen assemblages of lake cores or lacustrine profiles.

Vegetation and climate changes during the last 8660 cal.a BP in central Mongolia,based on a high-resolution pollen record from Lake Ugii Nuur

Based on modern pollen studies and reliable chronology of nine AMS 14C dates, a detailed history of vegetation and climate changes during the past 8660 cal. a BP was reconstructed by a high-resolution pollen record from Ugii Nuur in central Mongolia. Poaceae-steppe dominated the study area and the climate was mild and semi-humid before 7800 cal. a BP with a noticeable cool and humid interval at 8350―8250 cal. a BP. Xerophytic plant increased and the climate became warm and dry gradually since 7800 cal. a BP. From 6860 to 3170 cal. a BP, semi-desert steppe expanded, suggesting a prolonged warm and dry climate. Between 3170 and 2340 cal. a BP, regional forest steppe expanded whereas semi-desert steppe retreated, indicating the climate became cool and wet gradually and the humidity reached the maximum at the end of this stage. From 2340 to 1600 cal. a BP, a general cool and wet climate prevailed. And the climatic instability increased after 1600 cal. a BP. Review of regional pub-lished palaeoclimatic records implies that the mid-Holocene dry climate might have prevailed in vast areas from central Mongolia to arid areas of northwest China. Pollen-based climate reconstruction for UG04 core was well correlated with the result of climate model on Central Asia by Bush. In addition, several abrupt climatic events (cool and wet) were found and some could be broadly compared with the cool events in Atlantic.

Dust pollen distribution on a continental scale and its relation to present-day vegetation along north-south transects in east China

A series of dust pollen samples was collected along N-S transects in east China (18°N to 53°N latitudes). Sample sites extend from the cold-temperate zone in the north to the tropical region in the south. Pollen taxa characterize each region and reflect the natural and devastated vegetation as well as corre- sponding climatic zones. The quantitative pollen data can be used to estimate the spatial distribution of planted and introduced species. Valuable information of human disturbance of the natural forest is evaluated by quantitative comparison between dust pollen and in-situ pollen of protected forest. In addition, percentages of grass pollen vary regularly from north to south that is consistent with spatial distribution of net primary productivity in east China. Among all grasses, Artemisia and the Gramineae carry the clearest signal: their ratio increases northwards and therefore represent a suitable and con- venient tool for palaeoclimate reconstructions.

Vegetation and Climate Variations at Taibai, Qinling Mountains in Central China for the Last 3 500 cal BP

Pollen records of two swamp sections, located at Taibai Mountain, the highest peak in the Qinling Mountains of central China, show variations of vegetation and climate for the last 3 500 cal BP. The pollen assemblage at the Foyechi and Sanqingchi sections and the surface soil pollen allowed us to reconstruct a high-altitude vegetation history at Taibai Mountain for the first time. The data indicated that there was a cold-dry climate interval between 3 500 and 3 080 cal BP and a relatively warm and wet period compared with the present from 3 080 to 1 860 cal BE The warmest period in the late Holocene on Taibai Mountain was from 1 430 to 730 cal BP, with an approximate 2 ~C increase in mean annual temperature compared with today. There was a relatively cool-dry climate interval from 730 to 310 cal BE After 310 cal BE a mountain tundra vegetation developed again and the position of the modern tree line was established.

Spatial patterns of vegetation and climate in the North China Plain during the Last Glacial Maximum and Holocene climatic optimum

Reconstructing the spatial patterns of regional climate and vegetation during specific intervals in the past is important for assessing the possible responses of the ecological environment under future global warming scenarios. In this study, we reconstructed the history of regional vegetation and climate based on six radiocarbon-dated pollen records from the North China Plain. Combining the results with existing pollen records, we reconstruct the paleoenvironment of the North China Plain during the Last Glacial Maximum(LGM) and the Holocene Climatic Optimum(HCO). The results show that changes in the regional vegetation since the LGM were primarily determined by climatic conditions, the geomorphic landscape and by human activity.During the LGM, the climate was cold and dry;mixed broadleaf-coniferous forest and deciduous-evergreen broadleaf forest developed in the southern mountains, and cold-resistant coniferous forest and mixed broadleaf-coniferous forest were present in the northern mountains. The forest cover was relatively low, with mesophytic and hygrophilous meadow occupying the southern part of the plain, and temperate grassland and desert steppe were distributed in the north;Chenopodiaceae-dominated halophytes grew on the exposed continental shelf of the Bohai Sea and Yellow Sea. During the HCO, the climate was warm and wet;deciduous broadleaf forest and deciduous-evergreen broadleaf forest, with subtropical species, developed in the southern mountains, and deciduous broadleaf forest with thermophilic species was present in northern mountains. Although the degree of forest cover was greater than during the LGM, the vegetation of the plain area was still dominated by herbs, while halophytes had migrated inland due to sea level rise. In addition, the expansion of human activities, especially the intensification of cultivation,had a significant influence on the natural vegetation. Our results provide data and a scientific basis for paleoclimate modelling and regional carbon cycle assessment in north China, with implications for predicting changes in the ecological environment under future global warming scenarios.

Pollen-inferred vegetation and environmental changes since 16.7 ka BP at Balikun Lake, Xinjiang

A high-resolution fossil pollen record from the sedimentary cores of Balikun Lake, northwestern China, combined with modern surface pollen data, is used to reconstruct the history of vegetation and climatic change since 16.7 cal. ka BP. Fossil pollen assem-blages and lithology indicate that the study area was dominated by desert. The desert had extremely arid climate and lower effec-tive moisture during 16.7–7.9 cal. ka BP, especially from 16.7 to 8.9 cal. ka BP when the lake maybe dried up. During 8.9–7.9 cal. ka BP, the environment gradually recovered in this area. It was then followed by the optimum period from 7.9 to 4.3 cal. Ka BP, when the effective moisture obviously increased. It was characterized by the typical desert-steppe/steppe vegetation and was ac-companied with several patch-birch woodlands around the lake. After that, a short but extremely arid climatic event occurred during 4.3–3.8 cal. ka BP, and the vegetation quickly changed from desert-steppe/steppe to desert. It was a relatively optimum period from 3.8 to 0.53 cal. ka BP showing typical desert-steppe/meadow-steppe landscape. Since 0.53 cal. ka BP, the climate has shown signs of deteriorating again. Furthermore, regional comparison shows that the characteristics of climatic and environmental evolution in this area were clearly different from East Asia monsoonal area during the last 16.7 cal. ka BP. It was characterized by the arid climate during the late-glacial and early Holocene, and relatively wet during the mid-late Holocene.

Pollen-recorded climate changes between 13.0 and 7.0 ^(14)C ka BP in southern Ningxia,China

A pollen record from Haiyuan section in the southern part of Ningxia revealed a detailed history of vegetation variation and associated climate changes during the period from^13.0 to^7.0 14 C ka BP.A steppe landscape under a moderately dry(and probably cool)condition(~12.7-~12.1 14 C ka BP)was replaced by a coniferous forest dominating the landscape under a generally wet climate from^12.1 to ~11.01 4C ka BP.This generally wet period,corresponding to the European B?lling/All?rod period,can be divided into three stages:a cool and wet stage between^12.1 and^11.4 14 C ka BP,a mild and rela- tively dry stage between^11.4 and^11.2 14 C ka BP,and a mild and wet stage between^11.2 and^11.0 14 C ka BP.The coniferous forest-dominated landscape was then deteriorated into steppe landscape (~11.0-~10.6 14 C ka BP)and further into a desert steppe landscape from^10.6 to^9.8 14 C ka BP,being correspondent to the European Younger Dryas period.After a brief episode of a cool and wet climate (~9.8-~9.6 14 C ka BP),a relatively mild and dry condition prevailed during the early Holocene(~9.6- ~7.6 14 C ka BP)and then a warm and humid climate started the mid-Holocene(~7.6-~7.2 14 C ka BP).

An ice-core record of vegetation and climate changes in the central Tibetan Plateau during the last 550 years

We present a 550-year ice-core pollen record with a 5-year resolution from the Puruogangri ice field in the central Tibetan Plateau.Analysis of the relationship between pollen record and instrumental observations suggests that the sum of the steppe and meadow pollen taxa is a good indicator of summer (June-August) temperature,whereas the ratios of Cyperaceae/(Gramineae+Artemisia) [Cy/(G+A)] as well as M/S (meadow to steppe percentages) are indicative of humidity changes in this region.Together with δ18O and glacial accumulation records,the response of vegetation to climate change over the past 500 years was revealed.Desert vegetation dominated during 1450-1640 AD,a time period characterized by cold-wet climate,while steppe vegetation expanded during 1640-1915 when warm-dry climate prevailed.Afterwards,during a cold and humid period,desert vegetation expanded again.Since 1980-2002,due to the increase of summer temperatures,steppe and meadow vegetation predominates,while areas with desert vegetation are reduced.This proxy series is the first high-resolution ice-core pollen record spanning the last 550 years for the central Tibetan Plateau.

Abrupt vegetation shifts caused by gradual climate changes in central Asia during the Holocene

Understanding the response of ecosystems to past climate is critical for evaluating the impacts of future climate changes.A large-scale abrupt shift of vegetation in response to the Holocene gradual climate changes has been well documented for the Sahara-Sahel ecosystem. Whether such a non-linear response is of universal significance remains to be further addressed. Here,we examine the vegetation-climate relationships in central Asia based on a compilation of 38 high-quality pollen records. The results show that the Holocene vegetation experienced two major abrupt shifts, one in the early Holocene(Shift I, establishing shift) and another in the late Holocene(Shift II, collapsing shift), while the mid-Holocene vegetation remained rather stable. The timings of these shifts in different regions are asynchronous, which are not readily linkable with any known abrupt climate shifts,but are highly correlated with the local rainfalls. These new findings suggest that the observed vegetation shifts are attributable to the threshold effects of the orbital-induced gradual climate changes. During the early Holocene, the orbital-induced precipitation increase would have first reached the threshold for vegetation "establishment" for moister areas, but significantly later for drier areas. In contrast, the orbital-induced precipitation decrease during the late Holocene would have first reached the threshold, and led to the vegetation "collapse" for drier areas, but delayed for moister areas. The well-known 4.2 kyr BP drought event and human intervention would have also helped the vegetation collapses at some sites. These interpretations are strongly supported by our surface pollen-climate analyses and ecosystem simulations. These results also imply that future climate changes may cause abrupt changes in the dry ecosystem once the threshold is reached.

Vegetation evolution and mil-lennial-scale climatic fluctua-tions since Last Glacial Maximum in pollen record from northern South China Sea

In order to study vegetation evolution and en- vironmental change since the Last Glacial Maximum (LGM), a total of 180 pollen samples with an average time resolution of 150 years were analyzed on the top parts(0–31 m, 0–27 kaBP)of deep sea sediments from ODP Site 1144 (20°3.18′N, 1170°25.14′E), northeastern SCS. The character- istic fea- tures of pollen diagram include that pine dominates in the interglacial, and herb pollen dominates with a good deal of tropical-subtropical pollen in the last glacial, and from 18 kaBP the tropical-subtropical pollen influx rose abruptly, while the herbaceous pollen influx and percentage dropped quickly, indicating that climate turned warmer and more humid, and more tropical-subtropical vegetation grew on the mainland and the emerging continental shelf, while the grassland on the shelf diminished. A detailed comparison shows an earlier change of pollen assemblages at the glacial- interglacial transition between MIS6 and 5 (Termination II) than the ice volume change indicated by the oxygen isotope record, implying that mid-low latitude climate warming pre- ceded ice sheet retreat. Millennial-scale climatic fluctuations of vegetation change in pollen record are also discussed.

Response of forest distribution to past climate change: An insight into future predictions

Vegetation dynamics could lead to changes in the global carbon and hydrology cycle,as well as feedbacks to climate change.This paper reviews the response of forest dynamics to climate change.Based on palaeoecological studies,we summarized the features and modes of vegetation response to climate change and categorized the impacts of climate change on vegetation dynamics as three types:climate stress on vegetation,buffer effects by non-climatic factors,and perturbation of the vegetation distribution by stochastic events.Due to the openness of the vegetation system and the integrated effects of both climatic and non-climatic factors,the vegetation-climate relationship deviates far from its equilibrium.The vegetation distribution shows a non-linear response to climate change,which also makes it difficult to quantify the modern vegetation distribution in terms of specific climatic factors.Past analog,space-for-time-substitution and Dynamic Global Vegetation Models(DGVMs)are three approaches to predicting the future vegetation distribution,but they have all been established on the assumption of vegetation-climate equilibrium.We propose that improving DGVMs is a future task for studies of vegetation dynamics because these are process-based models incorporating both disturbance(e.g.fire)and the variability in Plant Functional Types(PFTs).However,palaeoecological results should be used to test the models,and issues like spatial and temporal scale,complexity of climate change,effects of non-climatic factors,vegetation-climate feedback,and human regulation on vegetation dynamics are suggested as topics for future studies.

A comparative study of n-alkane biomarker and pollen records: an example from southern China

We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the dis-crepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section. Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Bio-markers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C31/(C27+C29+C 31) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus im-proving the resolution and precision of vegetation and climate reconstruction.

中国西北沙漠毗邻区表土花粉与植被和气候的关系——古气候定量重建的尝试

为探讨中国西北沙漠毗邻区现代花粉、植被和气候之间的定性和定量关系,利用222个表土花粉样品、植被样方调查以及气象数据,进行指示种分析、花粉代表性分析、排序分析以及古气候定量重建尝试。结果表明,沙漠毗邻区的表土花粉可分为荒漠带(三个亚带)、灌丛带、草甸带、高山草甸带和林草过渡带5个带;各植被带中主要科属花粉的代表性均较低,且同种花粉不同区域代表性有较大差异;荒漠带2和灌丛带的花粉组合与植被调查一致性较差,其余植被带的花粉组合和植被调查结果均有较好的一致性;指示种分析以及排序分析表明除草甸带和高山草甸带样点区分度较差外,其余植被带样点之间均有较好的区分;年平均降水量、7月平均温度和1月平均温度是研究区3个重要的气候变量,其中年平均降水量是气候重建最理想的因素;利用加权偏最小二乘法(WA-PLS)和现代类比法(MAT)建立花粉—气候校准集,留一法交叉验证结果显示,WA-PLS预测性能优于MAT。

若尔盖地区25万年以来的植被与气候

本文根据ＲＭ孔上部６０ｍ２１０个样品的花粉分析结果，探讨了若尔盖地区２５万年以来的植被演替和气候变化。研究结果表明，若尔盖地区过去２５万年的植被演替和气候变化可划分为７个阶段。在约２５０－１９５ＫａＢ．Ｐ．（７阶段），植被以亚高山莎草草甸为主，气温和降水与现在接近。在１９５－１２８ＫａＢ．Ｐ．（６阶段）和３２－１１ＫａＢ．Ｐ．（２阶段），植被主要是荒漠草原，反映寒冷干旱的冰期气候，年平均气温比现在低５－６℃，年降水量仅为现在的６０－８０％左右。１２８－７１ＫａＢ．Ｐ．（５阶段）是过去２５万年中水热条件最好的时期，植被主要是亚高山暗针叶林和亚高山草甸，大部分时间的气温比现在高１℃左右，降水量稍高于现在；但在此阶段的气温和降水仍有较大的波动，５ｅ、５ｃ和５ａ阶段的气温和降水高于５ｂ和５ｄ阶段。７１－５８ＫａＢ．Ｐ．（４阶段）的植被主要是高山草甸为主，年平均气温比今低３－５℃，年降水量约为现在的８０％，在５８－３２ＫａＢ．Ｐ．（３阶段），早期植被以亚高山暗针叶林和草甸为主，晚期主要是亚高山禾草草甸，气温和降水均明显高于４阶段，在晚期气温呈非线性逐渐下降的趋势。

若尔盖地区22000年以来的植被与气候

若尔盖ＲＭ孔上部６３７ｃｍ的花粉分析研究表明，在２２０００－１８０００ａＢ．Ｐ．，植被以高山草甸和荒漠草原为主，气候较现在寒冷干燥；１８０００－１３０００ａＢ．Ｐ．，主要是高山、亚高山草甸，出现亚高山灌丛，气温趋于升高，但仍干燥；１３０００－１１０００ａＢ．Ｐ，植被以亚高山禾草草甸为主；亚高山灌丛发展，可能已出现亚高山常绿针叶林，气温进一步上升，到后期己接近现在，湿度有所增加；１１０００－７０００ａＢ．Ｐ．，亚高山常绿针叶林扩张，亚高山灌丛在地方性植被中的比重又有所增加，草甸除禾草草甸外，可能出现亚高山莎草草甸或沼泽草甸，气温和湿度均比前期增高，西南季风在１１０００ａＢ．Ｐ．前后侵入本区；７００００－３３００ａＢ．Ｐ．，亚高山常绿针叶林大规模扩张，亚高山灌丛基本上被其取代，地方性植被主要是禾草草甸和莎草草甸或沼泽草甸，气候温暖潮湿；３３００－１９００ａＢ．Ｐ．，亚高山常绿针叶林退缩，禾草草甸可能被杂草草甸所取代，仍有莎草草甸或沼泽草甸，气温下降，湿度下降，西南季风逐渐减弱；１９００－１４００ａＢ．Ｐ．；针叶林进一步退缩，且冷杉在针叶林中的含量大于云杉，莎草草甸或沼泽草甸的规模扩大，气温进一步下降；１４００ａ?

青藏高原东北部5000年来气候变化与若尔盖湿地历史生态学研究进展

全球变化背景下古气候学的研究越来越受到关注。利用多年来的文献记载和自然证据,对青藏高原东北部气候变化进行重建。并以若尔盖湿地为例,梳理了区域5000 a来气候变化对湿地植被类型、泥炭沼泽发育和文化发展产生的影响,探讨了气候变化、文化发展、沼泽发育三者之间可能具有的相互关系。指出青藏高原东北部5000—3000 a B.P.之间气候较为暖湿,其平均温度要高出现在2℃左右;3000 a B.P.至今为气候干冷期,其中1000 a B.P.左右是过去5000 a中最寒冷时期,近1000 a来气温呈缓慢回升趋势。区域的气候变化决定了植被类型,对泥炭沼泽的形成和发育发挥了重要作用,对文明进程的影响主要体现在气候变化通过影响沼泽的演替,从而改变人类活动的范围与早期文明的形成,同时人类的过度活动也在一定程度上影响了沼泽的分布格局及动态。但气候变化、沼泽发育和文化发展三者之间的关系有赖于多因素耦合,其具体机理有待更深入的研究。