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The article presents updated knowledge on climate change in Poland (central Europe) in the first half of the last millennium (1001–1500). This knowledge is required to delimit the existence, duration, and scale of the Medieval Warm Period (MWP, also called the Medieval Climate Anomaly, MCA, here). To this end, it employs all available quantitative climate reconstructions created for Poland in the last 2 decades and four new reconstructions using three dendrochronological series and an extensive database of historical source data on weather conditions. The growth of conifers in lowland and upland Poland depends on the temperature in the cold season, especially in February and March. All available reconstructions based on dendrochronology data represent this time of the year. Summer temperatures were reconstructed using biological proxies and documentary evidence. The latter, however, is limited to the 15th century only. Winter temperature was used as the proxy for annual temperature proxies instead of the more usual use of summer temperature. The MWP occurred in Poland probably from the late 12th century to the first halves of the 14th or 15th centuries. All the analysed quantitative reconstructions suggest that the MWP in Poland was comparable to or warmer than the mean temperature in the period 1951–2000. The coldest conditions in the entire study period were noted in the first half of the 11th century (both winter and summer) and the second half of the 15th century (only winter). The greatest climate continentality occurred in the 15th century. Good agreement was found between the reconstructions of Poland's climate and many reconstructions available for Europe. [ABSTRACT FROM AUTHOR]

Abstract: Tree ring width (TRW), maximum (MXD), mean (MED) and minimum (MID) wood density were investigated in samples from the vicinity of the Tuchola Forest Biosphere Reserve (Northern Poland) in an attempt to distinguish the relative importance of climate and insect attack on the growth of Norway spruce. Selected climate parameters were used for a multiple regression to predict tree-ring width during insect outbreaks. This also used AICc for model selection. Additionally, k-means clustering was then used to group the yearly data of TRW, MXD, MID and the data of insect outbreaks. The respective climate data and data on insect outbreaks during the years 1962–1996 revealed a strong influence of May precipitation on TRW and insect outbreaks on MID. Missing tree rings or narrow rings and lower MXD together with higher MID might indicate increased insect activity. [Copyright &y& Elsevier]

Most of the water in the River Nile originates from monsoonal rainfall over the Ethiopian Highlands. Despite warnings of future climate change, little is known about the historical variability in this supply, particularly at annual resolution. Development of tree-ring records in this region has been limited by the occurrence of bi- or multimodal rainfall regimes, causing the development of multiple growth rings that cannot be dated with confidence. In this study, we identified annual rings in 30 Juniperus procera trees from northwest Ethiopia by dendrochronology and AMS radiocarbon dating. Carbon isotope ratios (4 series) and ring widths (73 series) were measured. The carbon isotope series did not contain strong trends possibly attributable to increased anthropogenic atmospheric CO2 concentrations or the juvenile effect. Both carbon isotope values and ring widths were strongly correlated with Blue Nile baseflow, and from composite chronology indices (r=0.75, p < 0.01), a preliminary reconstruction of Blue Nile baseflow back to AD 1836 was developed. Subsample signal strength remained above 0.85 for most of the reconstruction. Uncertainty bands were relatively narrow and the reliability of the preliminary reconstruction was confirmed by correspondence with reported years of drought and famine. The preliminary reconstruction is characterized by an exceptional decline in baseflow during the late AD 1960s. Flows recovered during the late 1990s. Additional sampling is advised to increase replication, spatial coverage and length of the preliminary reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: The effects on tree growth of both climatic and non-climatic variables were investigated in relation to dune dynamics at three sites on the Czolpinska dune in the Slowinski National Park, Poland where aeolian sediments are invading a forest of Scots Pine (Pinus sylvestris L.). We found that where dune advance was relatively rapid, tree vitality declined after stem burial was over 1.9m, but where advance was under 1m/yr survival was remarkably increased, one tree survived, albeit with thinning needles, after an estimated 11.4m burial. Below sand-surface stem discs, cut 0.5m apart, from a heavily suppressed tree revealed a difference in narrow-ring reactions of up to 2years over a 2m burial distance; the discs also showed a time lag of 4years before compression wood formation. Consequently, when estimating sand-movement rates we discounted compression wood reactions; we also excluded climatic events and pest infestations. The remaining data supplied a sand-advance rate at Site 1 from 2.4 to 3.5m/yr. At Site 2, rates were from 1.2 to 2.5m/yr, with a direct measurement of 0.3m/yr between 2006 and 2007. At Site 3 rates were from 0.3 to 1.2m/yr, with dune migration here virtually at a standstill over the last seven years. Direct measurement of sand movement (3.03m/yr) at Site 1 was slower than the lowest rate (3.5m/yr) previously recorded by Borówka (1980) for the larger dune system. [Copyright &y& Elsevier]

Abstract: African pencil cedar (Juniperus procera Hochst. ex Endlicher 1847) is a tropical, irregularly growing species that can produce annual growth rings in response to an annual cycle of wet and dry seasons. In this paper, we assess the periodicity of growth-ring formation for 13 stem discs from a site in Central-Northern Ethiopia by crossdating and radiocarbon dating. The crossdating process is described more transparently than usual to allow open discussion of the methodology employed. Although the ring-width series could be tentatively matched, radiocarbon dating revealed that the growth rings of the junipers from the studied site are neither annual nor represent a common periodicity. It was found that the trees are exceptionally sensitive and respond individually to the complex local climate. For future research, it is recommended to select more mesic sites with an unambiguously unimodal rainfall regime and to gain external evidence to support assumptions about the periodicity of growth-ring formation in Juniperus procera. [Copyright &y& Elsevier]