18 research outputs found

    Subfossil bog-pine horizons document climate and ecosystem changes during the Mid-Holocene

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    Extended dendrochronological investigations were performed on subfossil pine entombed in peat layers of former raised bogs in Lower Saxony (NW Germany). The aim was to study of dynamics in bog development in response to local environmental conditions and regional changes in climate throughout the Holocene. To date, 1702 samples have been collected from 36 locations. Crossdating with the Lower Saxony Bog Oak Chronology (LSBOC) resulted in five absolutely dated pine chronologies covering large parts of the period from 5600 BC to 2200 BC. Radiocarbon dating of eight additional chronologies extends this time-span from 7000 BC to 1500 BC. By combining dendrochronology with information on stratigraphic position as well as stem and root morphology we found that major changes in site hydrology cause changes in growth pattern and population dynamics of subfossil pine whereas storm and fire were of minor importance. The fact that shifts in growth patterns and population dynamics occurred simultaneously in trees from different sites indicates regional climate changes as main drivers of pines forest development in peatland ecosystem

    Subfossil European bog oaks: population dynamics and long-term growth depressions as indicators of changes in the Holocene hydro-regime and climate

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    Some 2600 bog oaks have been dated from German, Dutch and Irish bogs covering the period 6000 bc to ad 1000. The ring patterns of these ‘bog oaks’ are characterized by recurrent, long-term growth depressions. In addition, obvious changes in the temporal distribution of the bog-oak trunks throughout the Holocene are found. Both features were probably caused by unfavourable growth conditions, which are most likely linked to changes in site hydrology.We use a new variable, ‘annual mean age’, as a tool to analyse the population dynamics of bog oaks in more detail, enabling the detection of synchronous intersite and interregional changes. It is calculated as the arithmetic mean of the age of all trees in each calendar year. We performed the calculation on regional (Germany, The Netherlands, Ireland) subsets of the bog-oak series. Abrupt changes in annual mean age are taken to indicate periods of generation change. We Ž find good agreement for the interval from 5000 bc to 2000 bc between the continental (combined German and Dutch) and the Irish mean-age chronologies. Most changes in population dynamics correspond with contemporary changes in the associated regional tree-ring chronologies. It is concluded that the observed changes in population dynamics and growth activity are responses to common environmental forcing, most likely related to climate

    Dendrochronology of the English Neolithic

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    In the period 1970-85, tree-ring research in Europe had resulted in the production of long oak chronologies for both Ireland and Germany going back over 7000 years (e.g. Brown et al. 1986; Leuschner &amp; Delorme 1984). In England, there was a network of regional chronologies covering the historic period, and almost no chronological coverage for the prehistoric. For the archaeologist this meant that, provided a site from the historic period produced a replicated site chronology, the chances of dating by dendrochronology were very high. The chances of this happening for a prehistoric site were poor by comparison, although some sites were successfully dated, for example the Iron Age causeway from Fiskerton in Liricolnshire and the Hasholme log boat found in North Humberside (Hillam 1987). The period 1985-88 saw an intense effort to outline a prehistoric oak tree-ring chronology in England (Baillie &amp; Brown 1988). This work centred on sub-fossil oaks from East Anglia and Lancashire and built on a previous chronology from Swan Carr, near Durham which spanned 1155-381 BC (Baillie et al. 1983). The approach to chronology-building was to produce wellreplicated chronology units which could be located precisely in time against the existing Irish (Pilcher et al. 1984) and North German (Leuschner &amp; Delorme 1984) chronologies.</p
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