TY - JOUR A1 - Wolter, Juliane A1 - Lantuit, Hugues A1 - Herzschuh, Ulrike A1 - Stettner, Samuel A1 - Fritz, Michael T1 - Tundra vegetation stability versus lake-basin variability on the Yukon Coastal Plain (NW Canada) during the past three centuries JF - The Holocene : an interdisciplinary journal focusing on recent environmental change KW - pollen Y1 - 2017 U6 - https://doi.org/10.1177/0959683617708441 SN - 0959-6836 SN - 1477-0911 VL - 27 SP - 1846 EP - 1858 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Niemeyer, Bastian A1 - Herzschuh, Ulrike A1 - Pestryakova, Luidmila Agafyevna T1 - Vegetation and lake changes on the southern Taymyr peninsula, northern Siberia, during the last 300 years inferred from pollen and Pediastrum green algae records JF - The Holocene : an interdisciplinary journal focusing on recent environmental change N2 - Siberian arctic vegetation and lake water communities, known for their temperature dependence, are expected to be particularly impacted by recent climate change and high warming rates. However, decadal information on the nature and strength of recent vegetation change and its time lag to climate signals are rare. In this study, we present a Pb-210/Cs-137 dated pollen and Pediastrum species record from a unnamed lake in the south of the Taymyr peninsula covering the period from AD 1706 to 2011. Thirty-nine palynomorphs and 10 morphotypes of Pediastrum species were studied to assess changes in vegetation and lake conditions as probable responses to climate change. We compared the pollen record with Pediastrum species, which we consider to be important proxies of climate changes. Three pollen assemblage zones characterised by Betula nana, Alnus viridis and Larix gmelinii (1706-1808); herbs such as Cyperaceae, Artemisia or Senecio (1808-1879), and higher abundance of Larix pollen (1955-2011) are visible. Also, three Pediastrum assemblage zones show changes of aquatic conditions: higher abundances of Pediastrum boryanum var. brevicorne (1706-1802); medium abundances of P. kawraiskyi and P. integrum (1802-1840 and 1920-1980), indicating cooler conditions while less eutrophic conditions are indicated by P. boryanum, and a mainly balanced composition with only small changes of cold- and warm-adapted Pediastrum species (1965-2011). In general, compositional Pediastrum species turnover is slightly higher than that indicated by pollen data (0.54 vs 0.34 SD), but both are only minor for this treeline location. In conclusion, the relevance of differentiation of Pediastrum species is promising and can give further insights into the relationship between lakes and their surrounding vegetation transferred onto climatic conditions. KW - morphotypes KW - Pediastrum KW - pollen KW - Siberia KW - treeline KW - vegetation Y1 - 2015 U6 - https://doi.org/10.1177/0959683614565954 SN - 0959-6836 SN - 1477-0911 VL - 25 IS - 4 SP - 596 EP - 606 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Li, Wenjia A1 - Tian, Fang A1 - Rudaya, Natalya A. A1 - Herzschuh, Ulrike A1 - Cao, Xianyong T1 - Pollen-based holocene thawing-history of permafrost in Northern Asia and its potential impacts on climate change JF - Frontiers in Ecology and Evolution N2 - As the recent permafrost thawing of northern Asia proceeds due to anthropogenic climate change, precise and detailed palaeoecological records from past warm periods are essential to anticipate the extent of future permafrost variations. Here, based on the modern relationship between permafrost and vegetation (represented by pollen assemblages), we trained a Random Forest model using pollen and permafrost data and verified its reliability to reconstruct the history of permafrost in northern Asia during the Holocene. An early Holocene (12-8 cal ka BP) strong thawing trend, a middle-to-late Holocene (8-2 cal ka BP) relatively slow thawing trend, and a late Holocene freezing trend of permafrost in northern Asia are consistent with climatic proxies such as summer solar radiation and Northern Hemisphere temperature. The extensive distribution of permafrost in northern Asia inhibited the spread of evergreen coniferous trees during the early Holocene warming and might have decelerated the enhancement of the East Asian summer monsoon (EASM) by altering hydrological processes and albedo. Based on these findings, we suggest that studies of the EASM should consider more the state of permafrost and vegetation in northern Asia, which are often overlooked and may have a profound impact on climate change in this region. KW - pollen KW - Random Forest KW - Siberia KW - East Asian summer monsoon KW - permafrost Y1 - 2022 U6 - https://doi.org/10.3389/fevo.2022.894471 SN - 2296-701X VL - 10 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Tian, Fang A1 - Herzschuh, Ulrike A1 - Mischke, Steffen A1 - Schluetz, Frank T1 - What drives the recent intensified vegetation degradation in Mongolia - Climate change or human activity? JF - The Holocene : an interdisciplinary journal focusing on recent environmental change N2 - This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977-1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of C-13(org) and N-15 since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area. KW - central Mongolia KW - grain size KW - human impact KW - lake eutrophication KW - pollen KW - vegetation degradation Y1 - 2014 U6 - https://doi.org/10.1177/0959683614540958 SN - 0959-6836 SN - 1477-0911 VL - 24 IS - 10 SP - 1206 EP - 1215 PB - Sage Publ. CY - London ER - TY - JOUR A1 - Wischnewski, Juliane A1 - Kramer, Annette A1 - Kong, Zhaochen A1 - Mackay, Anson W. A1 - Simpson, Gavin L. A1 - Mischke, Steffen A1 - Herzschuh, Ulrike T1 - Terrestrial and aquatic responses to climate change and human impact on the southeastern Tibetan Plateau during the past two centuries JF - Global change biology N2 - Rapid population growth and economic development have led to increased anthropogenic pressures on the Tibetan Plateau, causing significant land cover changes with potentially severe ecological consequences. To assess whether or not these pressures are also affecting the remote montane-boreal lakes on the SE Tibetan Plateau, fossil pollen and diatom data from two lakes were synthesized. The interplay of aquatic and terrestrial ecosystem response was explored in respect to climate variability and human activity over the past 200 years. Nonmetric multidimensional scaling and Procrustes rotation analysis were undertaken to determine whether pollen and diatom responses in each lake were similar and synchronous. Detrended canonical correspondence analysis was used to develop quantitative estimates of compositional species turnover. Despite instrumental evidence of significant climatic warming on the southeastern Plateau, the pollen and diatom records indicate very stable species composition throughout their profiles and show only very subtle responses to environmental changes over the past 200 years. The compositional species turnover (0.36-0.94 SD) is relatively low in comparison to the species reorganizations known from the periods during the mid-and early-Holocene (0.64-1.61 SD) on the SE Plateau, and also in comparison to turnover rates of sediment records from climate-sensitive regions in the circum arctic. Our results indicate that climatically induced ecological thresholds are not yet crossed, but that human activity has an increasing influence, particularly on the terrestrial ecosystem in our study area. Synergistic processes of post-Little Ice Age warming, 20th century climate warming and extensive reforestations since the 19th century have initiated a change from natural oak-pine forests to seminatural, likely less resilient pine-oak forests. Further warming and anthropogenic disturbances would possibly exceed the ecological threshold of these ecosystems and lead to severe ecological consequences. KW - climate change KW - compositional species turnover KW - diatoms KW - human impact KW - pollen KW - Procrustes rotation KW - Tibetan Plateau Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2486.2011.02474.x SN - 1354-1013 VL - 17 IS - 11 SP - 3376 EP - 3391 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Glückler, Ramesh A1 - Geng, Rongwei A1 - Grimm, Lennart A1 - Baisheva, Izabella A1 - Herzschuh, Ulrike A1 - Stoof-Leichsenring, Kathleen R. A1 - Kruse, Stefan A1 - Andreev, Andrej Aleksandrovic A1 - Pestryakova, Luidmila A1 - Dietze, Elisabeth T1 - Holocene wildfire and vegetation dynamics in Central Yakutia, Siberia, reconstructed from lake-sediment proxies JF - Frontiers in Ecology and Evolution N2 - Wildfires play an essential role in the ecology of boreal forests. In eastern Siberia, fire activity has been increasing in recent years, challenging the livelihoods of local communities. Intensifying fire regimes also increase disturbance pressure on the boreal forests, which currently protect the permafrost beneath from accelerated degradation. However, long-term relationships between changes in fire regime and forest structure remain largely unknown. We assess past fire-vegetation feedbacks using sedimentary proxy records from Lake Satagay, Central Yakutia, Siberia, covering the past c. 10,800 years. Results from macroscopic and microscopic charcoal analyses indicate high amounts of burnt biomass during the Early Holocene, and that the present-day, low-severity surface fire regime has been in place since c. 4,500 years before present. A pollen-based quantitative reconstruction of vegetation cover and a terrestrial plant record based on sedimentary ancient DNA metabarcoding suggest a pronounced shift in forest structure toward the Late Holocene. Whereas the Early Holocene was characterized by postglacial open larch-birch woodlands, forest structure changed toward the modern, mixed larch-dominated closed-canopy forest during the Mid-Holocene. We propose a potential relationship between open woodlands and high amounts of burnt biomass, as well as a mediating effect of dense larch forest on the climate-driven intensification of fire regimes. Considering the anticipated increase in forest disturbances (droughts, insect invasions, and wildfires), higher tree mortality may force the modern state of the forest to shift toward an open woodland state comparable to the Early Holocene. Such a shift in forest structure may result in a positive feedback on currently intensifying wildfires. These new long-term data improve our understanding of millennial-scale fire regime changes and their relationships to changes of vegetation in Central Yakutia, where the local population is already being confronted with intensifying wildfire seasons. KW - fire KW - larch KW - boreal KW - forest KW - Russia KW - charcoal KW - pollen KW - ancient DNA Y1 - 2022 U6 - https://doi.org/10.3389/fevo.2022.962906 SN - 2296-701X VL - 10 PB - Frontiers Media CY - Lausanne ER -