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    • "While the primeval mid-Holocene forests of Central Europe are regarded as largely closed (Birks, 2005; Mitchell, 2005; more open conditions have been suggested by; Vera, 2000), the forests of the early Holocene are mostly considered rather open (Firbas, 1949; Tallantire, 2002; Giesecke et al., 2011). We arrive at an overall openness of 10e40% after the full expansion of birch, pine and hazel which may either represent open forests with a dense herbal layer ('savannah') or a mosaic of open vegetation within dense forests ('forest steppe'). "
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    ABSTRACT: The warming at the Younger Dryas–Holocene transition (∼11,600 cal. BP) triggered the rearrangement of vegetation across Europe. To better understand that response, we analysed both an extended fossil pollen data set and robust present-day site parameters from NE Germany in a data model comparison approach. This approach allowed to quantify past plant abundances in sub-regional landscape patterns, as defined by soil types and relief. Betula was the first tree taxon to expand from scattered stands that already existed during the Younger Dryas. The major tree taxa Betula and Pinus fully established after 200–400 years as largely separated stands of Pinus on well drained sandy and Betula on fertile morainic soils. Corylus started to spread after 11,200 cal. BP, yet the final expansion was delayed until ∼10,800 cal. BP. Corylus established on gleyic soils, from which it largely expelled Betula. Throughout the first two millennia of the Holocene, open grasslands existed on fine grained soils, where seasonal dryness prevented the establishment of deciduous trees.
    Quaternary Science Reviews 04/2014; 90:183–198. DOI:10.1016/j.quascirev.2014.03.002 · 4.57 Impact Factor
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    • "At the scale of hundreds to a thousand kilometres within individual regions, we recorded little or no directional pattern in the Alnus expansion, i.e., sites with Alnus evidence initially occurred across the whole region, and then the number of sites increased equally. We recorded this pattern in all northern regions, including the deglaciated area of Scandinavia, corroborating the descriptions of Bennett and Birks [95] for the British Isles and Giesecke et al. [18] for the Baltic area. Such a general absence of spatial coherence of the Alnus expansion within large areas seems to be very specific in comparison with the generally observed “stepping stone” character of expansions commonly recorded for other European trees [95]. "
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    ABSTRACT: Recently, new palaeoecological records supported by molecular analyses and palaeodistributional modelling have provided more comprehensive insights into plant behaviour during the last Quaternary cycle. We reviewed the migration history of species of subgenus Alnus during the last 50,000 years in Europe with a focus on (1) a general revision of Alnus history since the Last Glacial Maximum (LGM), (2) evidence of northern refugia of Alnus populations during the LGM and (3) the specific history of Alnus in particular European regions. We determined changes in Alnus distribution on the basis of 811 and 68 radiocarbon-dated pollen and macrofossil sites, respectively. We compiled data from the European Pollen Database, the Czech Quaternary Palynological Database, the Eurasian Macrofossil Database and additional literature. Pollen percentage thresholds indicating expansions or retreats were used to describe patterns of past Alnus occurrence. An expansion of Alnus during the Late Glacial and early Holocene periods supports the presence of alders during the LGM in southern peninsulas and northerly areas in western Europe, the foothills of the Alps, the Carpathians and northeastern Europe. After glaciers withdrew, the ice-free area of Europe was likely colonized from several regional refugia; the deglaciated area of Scandinavia was likely colonized from a single refugium in northeastern Europe. In the more northerly parts of Europe, we found a scale-dependent pattern of Alnus expansion characterised by a synchronous increase of Alnus within individual regions, though with regional differences in the times of the expansion. In southern peninsulas, the Alps and the Carpathians, by contrast, it seems that Alnus expanded differently at individual sites rather than synchronously in whole regions. Our synthesis supports the idea that northern LGM populations were important sources of postglacial Alnus expansion. The delayed Alnus expansion apparent in some regions was likely a result of environmental limitations.
    PLoS ONE 02/2014; 9(2):e88709. DOI:10.1371/journal.pone.0088709 · 3.23 Impact Factor
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    • "These palaeolimnological records, which span thousands of years, suggest that these current taxon-specific shifts are in response to an overriding effect of climate and, perhaps, they are an early indication of expected abrupt and general ecosystem shifts (Barnosky et al. 2012). In fact, Holocene and Late Glacial sediment records show that abrupt and large vegetation changes may occur in response to climate fluctuations within the range projected for the coming decades (Giesecke et al. 2011 "
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    ABSTRACT: Over recent decades, palaeolimnological records from remote sites have provided convincing evidence for the onset and development of several facets of global environmental change. Remote lakes, defined here as those occurring in high latitude or high altitude regions, have the advantage of not being overprinted by local anthropogenic processes. As such, many of these sites record broad-scale environmental changes, frequently driven by regime shifts in the Earth system. Here, we review a selection of studies from North America and Europe and discuss their broader implications. The history of investigation has evolved synchronously with the scope and awareness of environmental problems. An initial focus on acid deposition switched to metal and other types of pollutants, then climate change and eventually to atmospheric deposition-fertilising effects. However, none of these topics is independent of the other, and all of them affect ecosystem function and biodiversity in profound ways. Currently, remote lake palaeolimnology is developing unique datasets for each region investigated that benchmark current trends with respect to past, purely natural variability in lake systems. Fostering conceptual and methodological bridges with other environmental disciplines will upturn contribution of remote lake palaeolimnology in solving existing and emerging questions in global change science and planetary stewardship.
    Journal of Paleolimnology 03/2013; 49(3-3):513-535. DOI:10.1007/s10933-013-9681-2 · 2.12 Impact Factor
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