@article{WangHerzschuhShumilovskikhetal.2014, author = {Wang, Y. and Herzschuh, Ulrike and Shumilovskikh, L. S. and Mischke, Steffen and Birks, H. John B. and Wischnewski, J. and B{\"o}hner, J{\"u}rgen and Schluetz, F. and Lehmkuhl, F. and Diekmann, Bernhard and Wuennemann, B. and Zhang, C.}, title = {Open Access Quantitative reconstruction of precipitation changes on the NE Tibetan Plateau since the Last Glacial Maximum - extending the concept of pollen source area to pollen-based climate reconstructions from large lakes}, series = {Climate of the past : an interactive open access journal of the European Geosciences Union}, volume = {10}, journal = {Climate of the past : an interactive open access journal of the European Geosciences Union}, number = {1}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1814-9324}, doi = {10.5194/cp-10-21-2014}, pages = {21 -- 39}, year = {2014}, abstract = {Pollen records from large lakes have been used for quantitative palaeoclimate reconstruction, but the influences that lake size (as a result of species-specific variations in pollen dispersal patterns that smaller pollen grains are more easily transported to lake centre) and taphonomy have on these climatic signals have not previously been systematically investigated. We introduce the concept of pollen source area to pollen-based climate calibration using the north-eastern Tibetan Plateau as our study area. We present a pollen data set collected from large lakes in the arid to semi-arid region of central Asia. The influences that lake size and the inferred pollen source areas have on pollen compositions have been investigated through comparisons with pollen assemblages in neighbouring lakes of various sizes. Modern pollen samples collected from different parts of Lake Donggi Cona (in the north-eastern part of the Tibetan Plateau) reveal variations in pollen assemblages within this large lake, which are interpreted in terms of the species-specific dispersal and depositional patterns for different types of pollen, and in terms of fluvial input components. We have estimated the pollen source area for each lake individually and used this information to infer modern climate data with which to then develop a modern calibration data set, using both the multivariate regression tree (MRT) and weighted-averaging partial least squares (WA-PLS) approaches. Fossil pollen data from Lake Donggi Cona have been used to reconstruct the climate history of the north-eastern part of the Tibetan Plateau since the Last Glacial Maximum (LGM). The meanannual precipitation was quantitatively reconstructed using WA-PLS: extremely dry conditions are found to have dominated the LGM, with annual precipitation of around 100 mm, which is only 32\% of present-day precipitation. A gradually increasing trend in moisture conditions during the Late Glacial is terminated by an abrupt reversion to a dry phase that lasts for about 1000 yr and coincides with "Heinrich event 1" in the North Atlantic region. Subsequent periods corresponding to the Bolling/Allerod interstadial, with annual precipitation (P-ann) of about 350 mm, and the Younger Dryas event (about 270 mm P-ann) are followed by moist conditions in the early Holocene, with annual precipitation of up to 400 mm. A drier trend after 9 cal. ka BP is followed by a second wet phase in the middle Holocene, lasting until 4.5 cal. ka BP. Relatively steady conditions with only slight fluctuations then dominate the late Holocene, resulting in the present climatic conditions. The climate changes since the LGM have been primarily driven by deglaciation and fluctuations in the intensity of the Asian summer monsoon that resulted from changes in the Northern Hemisphere summer solar insolation, as well as from changes in the North Atlantic climate through variations in the circulation patterns and intensity of the westerlies.}, language = {en} } @article{MarquerGaillardSugitaetal.2017, author = {Marquer, Laurent and Gaillard, Marie-Jose and Sugita, Shinya and Poska, Anneli and Trondman, Anna-Kari and Mazier, Florence and Nielsen, Anne Birgitte and Fyfe, Ralph M. and Jonsson, Anna Maria and Smith, Benjamin and Kaplan, Jed O. and Alenius, Teija and Birks, H. John B. and Bjune, Anne E. and Christiansen, Jorg and Dodson, John and Edwards, Kevin J. and Giesecke, Thomas and Herzschuh, Ulrike and Kangur, Mihkel and Koff, Tiiu and Latalowa, Maligorzata and Lechterbeck, Jutta and Olofsson, Jorgen and Seppa, Heikki}, title = {Quantifying the effects of land use and climate on Holocene vegetation in Europe}, series = {Quaternary science reviews : the international multidisciplinary research and review journal}, volume = {171}, journal = {Quaternary science reviews : the international multidisciplinary research and review journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2017.07.001}, pages = {20 -- 37}, year = {2017}, abstract = {Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{HerzschuhBirksLiuetal.2010, author = {Herzschuh, Ulrike and Birks, H. John B. and Liu, Xingqi and Kubatzki, Claudia and Lohmann, Gerrit}, title = {Retracted: What caused the mid-Holocene forest decline on the eastern Tibet-Qinghai Plateau?}, issn = {1466-822X}, doi = {10.1111/j.1466-8238.2009.00501.x}, year = {2010}, abstract = {Aim: Atmospheric CO2 concentrations depend, in part, on the amount of biomass locked up in terrestrial vegetation. Information on the causes of a broad-scale vegetation transition and associated loss of biomass is thus of critical interest for understanding global palaeoclimatic changes. Pollen records from the north-eastern Tibet-Qinghai Plateau reveal a dramatic and extensive forest decline beginning c. 6000 cal. yr bp. The aim of this study is to elucidate the causes of this regional-scale change from high-biomass forest to low-biomass steppe on the Tibet-Qinghai Plateau during the second half of the Holocene. Location: Our study focuses on the north-eastern Tibet-Qinghai Plateau. Stratigraphical data used are from Qinghai Lake (3200 m a.s.l., 36 degrees 32'-37 degrees 15' N, 99 degrees 36'-100 degrees 47' E). Methods: We apply a modern pollen-precipitation transfer function from the eastern and north-eastern Tibet-Qinghai Plateau to fossil pollen spectra from Qinghai Lake to reconstruct annual precipitation changes during the Holocene. The reconstructions are compared to a stable oxygen-isotope record from the same sediment core and to results from two transient climate model simulations. Results: The pollen-based precipitation reconstruction covering the Holocene parallels moisture changes inferred from the stable oxygen-isotope record. Furthermore, these results are in close agreement with simulated model-based past annual precipitation changes. Main conclusions: In the light of these data and the model results, we conclude that it is not necessary to attribute the broad-scale forest decline to human activity. Climate change as a result of changes in the intensity of the East Asian Summer Monsoon in the mid-Holocene is the most parsimonious explanation for the widespread forest decline on the Tibet-Qinghai Plateau. Moreover, climate feedback from a reduced forest cover accentuates increasingly drier conditions in the area, indicating complex vegetation-climate interactions during this major ecological change.}, language = {en} } @article{HerzschuhPestryakovaSavelievaetal.2013, author = {Herzschuh, Ulrike and Pestryakova, Luidmila Agafyevna and Savelieva, Larissa A. and Heinecke, Liv and B{\"o}hmer, Thomas and Biskaborn, Boris and Andreev, Andrei and Ramisch, Arne and Shinneman, Avery L. C. and Birks, H. John B.}, title = {Siberian larch forests and the ion content of thaw lakes form a geochemically functional entity}, series = {Nature Communications}, volume = {4}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/ncomms3408}, pages = {8}, year = {2013}, abstract = {Siberian larch forests growing on shallow permafrost soils have not, until now, been considered to be controlling the abiotic and biotic characteristics of the vast number of thaw-lake ecosystems. Here we show, using four independent data sets (a modern data set from 201 lakes from the tundra to taiga, and three lake-core records), that lake-water geochemistry in Yakutia is highly correlated with vegetation. Alkalinity increases with catchment forest density. We postulate that in this arid area, higher evapotranspiration in larch forests compared with that in the tundra vegetation leads to local salt accumulation in soils. Solutes are transported to nearby thaw lakes during rain events and snow melt, but are not fully transported into rivers, because there is no continuous groundwater flow within permafrost soils. This implies that potentially large shifts in the chemical characteristics of aquatic ecosystems to known warming are absent because of the slow response of catchment forests to climate change.}, language = {en} } @article{WangLiuHerzschuhetal.2012, author = {Wang, Yongbo and Liu, Xingqi and Herzschuh, Ulrike and Yang, Xiangdong and Birks, H. John B. and Zhang, Enlou and Tong, Guobang}, title = {Temporally changing drivers for late-Holocene vegetation changes on the northern Tibetan Plateau}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {353}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, number = {8}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2012.06.022}, pages = {10 -- 20}, year = {2012}, abstract = {Fossil pollen records have been widely used as indicators of past changes in vegetation and variations in climate. The driving mechanisms behind these vegetation changes have, however, remained unclear. In order to evaluate vegetation changes that have occurred in the northern part of the Tibetan Plateau and the possible drivers behind these changes, we have applied a moving-window Redundancy Analysis (RDA) to high resolution (10-15 years) pollen and sedimentary data from Lake Kusai covering the last 3770 years. Our analyses reveal frequent fluctuations in the relative abundances of alpine steppe and alpine desert components. The sedimentary proxies (including total organic carbon content, total inorganic carbon content, and "end-member" indices from grain-size analyses) that explain statistically some of the changes in the pollen assemblage vary significantly with time, most probably reflecting multiple underlying driving processes. Climate appears to have had an important influence on vegetation changes when conditions were relatively wet and stable. However, a gradual decrease in vegetation cover was identified after 1500 cal a BP, after which the vegetation appears to have been affected more by extreme events such as dust-storms or fluvial erosion than by general climatic trends. Furthermore, pollen spectra over the last 600 years are shown by Procrustes analysis to be statistically different from those recovered from older samples, which we attribute to increased human impact that resulted in unprecedented changes to the vegetation composition. Overall, changes in vegetation and climate on the northern part of the Tibetan Plateau appear to have roughly followed the evolution of the Asian Summer Monsoon. After taking into account the highly significant millennial (1512 years) periodicity revealed by time-series analysis, the regional vegetation and climate changes also show variations that appear to match variations in the mid-latitude westerlies.}, language = {en} }