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Tree-ring chronologies provide high-resolution late Quaternary palaeoclimatic data. An important aim of tree-ring research is to extend the chronologies back in time, before the period covered by old living trees. Tree-ring material from historic buildings offers an opportunity to develop long chronologies that, in some regions, may cover the period of the past millennium. Such materials have remained in conditions favourable to preservation and can be used to date the construction timber by means of dendrochronology. Apart from dating, tree-ring data may prove valuable in interpreting past climatic conditions. Here we analyse the data of 111 Scots pine (Pinus sylvestris L.) tree-ring series from the Åland Islands in south-western Finland. In so doing, we illustrate the variation of wetness and drought in the region over a historical time frame (1057–1826). Non-climatic trends were removed from these series using alternative types of detrending procedures. Tree-ring chronologies constructed from the same raw data but using different types of detrending methods agreed on annual to subcentennial scales. The chronologies produced using regional curve standardization (RCS), preferably combined with implementation of a signal-free approach, were comparable with previously published sedimentary and tree-ring evidence from the same region. While non-RCS methods are effective in removing non-climatic information from the chronology, they also resulted in removal of the long-term variation (low-frequency), which did, at least in our data, represent the palaeoclimatic signal common to different types of proxy records. These records, including our data and those of gridded reconstructions developed previously as the Old World Drought Atlas, agreed in indicating dry conditions over the pre-1250 period and around the mid-15th century. The Åland chronology is characterized by notable fluctuations in the availability of tree-ring samples; the periods with low sample replication probably pinpoint years when large construction projects were suspended on these islands. [ABSTRACT FROM AUTHOR]

Tree-ring widths from 880 living, dry dead, and subfossil northern Swedish pines (Pinus sylvestris L.) have been assembled into a continuous and precisely dated chronology (the Torneträsk chronology) covering the period 5407 BC to AD 1997. Biological trends in the data were removed with autoregressive standardization (ARS) to emphasize year-to-year variability, and with regional curve standardization (RCS) to emphasize variability on timescales from decades to centuries. The strong association with summer mean temperature (June-August) has enabled the production of a temperature reconstruction for the last 7400 years, providing information on natural summer-temperature variability on timescales from years to centuries. Numerous cold episodes, comparable in severity and duration to the severe summers of the seventeenth century, are shown throughout the last seven millennia. Particularly severe conditions suggested between 600 and 1 BC correspond to a known period of glacier expansion. The relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals, although replication is relatively poor and confidence in the reconstructions is correspondingly reduced in the pre-Christian period, particularly around 3000, 1600 and 330 BC. Despite the use of the RCS approach in chronology construction, the 7400-year chronology does not express the full range of millennial-timescale temperature change in northern Sweden. [ABSTRACT FROM AUTHOR]

Pollen, plant macrofossils and charcoal were analysed from a lake-sediment sequence, including a refuse layer, from the Late Mesolithic settlement at Bökeberg III, southern Sweden. The chronology was established by means of AMS-dated plant macroremains. The results of the biostratigraphical studies indicate two settlement phases (A and B), at ca. 6650-6400 B.P. (5560-5320 cal. B.C.) and ca. 6150-5800 B.P. (5200-4680 cal. B.C.), respectively. The two settlement phases are associated with periods of low lake-level contemporaneous with the second major period of low lake levels during the Holocene in southern Sweden, and thus with a period of generally drier climate. The pollen analytical data suggest only minor human impact on the local vegetation during the two settlement phases. Three elm declines at ca. (1) 6200 B.P. (5200-5100 cal. B.C.), (2) 5450 B.P. (4340 cal. B.C.), and (3) 5150 B.P. (3980 cal. B.C.) are discussed. Elm decline 3 is synchronous with the classical north-west European elm decline. Elm declines 2 and 3 may be due to outbreaks of elm disease rather than to strong human impact or climate change. The charcoal analyses show that wood of a wide range of species was collected for fuel or other purposes. During phase A, plants used included acorns, hazelnuts and, possibly, Cornus sanguinea, and also Prunus spinosa, Sorbus aucuparia and Rubus idaeus. There is convincing evidence that Cladium mariscus was used for thatching. The second occupation phase, B, is characterised by the use of hazelnuts for food. The possible use of several other identified species is discussed. [ABSTRACT FROM AUTHOR]