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Forest and steppe communities in the Altai region of Central Asia are threatened by changing climate and anthropogenic pressure. Specifically, increasing drought and grazing pressure may cause collapses of moisture-demanding plant communities, particularly forests. Knowledge about past vegetation and fire responses to climate and land use changes may help anticipating future ecosystem risks, given that it has the potential to disclose mechanisms and processes that govern ecosystem vulnerability. We present a unique paleoecological record from the high-alpine Tsambagarav glacier in the Mongolian Altai that provides novel large-scale information on vegetation, fire and pollution with an exceptional temporal resolution and precision. Our palynological record identifies several late-Holocene boreal forest expansions, contractions and subsequent recoveries. Maximum forest expansions occurred at 3000-2800 BC, 2400-2100 BC, and 1900-1800 BC. After 1800 BC mixed boreal forest communities irrecoverably declined. Fires reached a maximum at 1600 BC, 200 years after the final forest collapse. Our multiproxy data suggest that burning peaked in response to dead biomass accumulation resulting from forest diebacks. Vegetation and fire regimes partly decoupled from climate after 1700 AD, when atmospheric industrial pollution began, and land use intensified. We conclude that moisture availability was more important than temperature for past vegetation dynamics, in particular for forest loss and steppe expansion. The past Mongolian Altai evidence implies that in the future forests of the Russian Altai may collapse in response to reduced moisture availability.
Woodlands and steppes
(2018)
Based on fossil organism remains including plant macrofossils, charcoal, pollen, and invertebrates preserved in syngenetic deposits of the Batagay permafrost sequence in the Siberian Yana Highlands, we reconstructed the environmental history during marine isotope stages (MIS) 6 to 2. Two fossil assemblages, exceptionally rich in plant remains, allowed for a detailed description of the palaeo-vegetation during two climate extremes of the Late Pleistocene, the onset of the last glacial maximum (LGM) and the last interglacial. In addition, altogether 41 assemblages were used to outline the vegetation history since the penultimate cold stage of MIS 6. Accordingly, meadow steppes analogue to modern communities of the phytosociological order Festucetalia lenensis formed the primary vegetation during the Saalian and Weichselian cold stages. Cold-resistant tundra-steppe communities (Carici rupestris-Kobresietea bellardii) as they occur above the treeline today were, in contrast to more northern locations, mostly lacking. During the last interglacial, open coniferous woodland similar to modern larch taiga was the primary vegetation at the site. Abundant charcoal indicates wildfire events during the last interglacial. Zoogenic disturbances of the local vegetation were indicated by the presence of ruderal plants, especially by abundant Urtica dioica, suggesting that the area was an interglacial refugium for large herbivores. Meadow steppes, which formed the primary vegetation during cold stages and provided potentially suitable pastures for herbivores, were a significant constituent of the plant cover in the Yana Highlands also under the full warm stage conditions of the last interglacial. Consequently, meadow steppes occurred in the Yana Highlands during the entire investigated timespan from MIS 6 to MIS 2 documenting a remarkable environmental stability. Thus, the proportion of meadow steppe vegetation merely shifted in response to the respectively prevailing climatic conditions. Their persistence indicates low precipitation and a relatively warm growing season throughout and beyond the late Pleistocene. The studied fossil record also proves that modern steppe occurrences in the Yana Highlands did not establish as late as in the Holocene but instead are relicts of a formerly continuous steppe belt extending from Central Siberia to Northeast Yakutia during the Pleistocene. The persistence of plants and invertebrates characteristic of meadow steppe vegetation in interior Yakutia throughout the late Quaternary indicates climatic continuity and documents the suitability of this region as a refugium also for other organisms of the Pleistocene mammoth steppe including the iconic large herbivores. (C)2018 Elsevier Ltd. All rights reserved.