Samuli Helama

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The birth sex ratio of vertebrates with chromosomal sex determination has been shown to respond to environmental variability, such as temperature. However, in humans the few previous studies on environmental temperature and birth sex ratios have produced mixed results. We examined whether reconstructed annual mean temperatures were associated with annual(More)
  • Samuli Helama, Jan Kresten, Nielsen, Ilmari Valovirta, Riassunto Il
  • 2007
Shells of Finnish freshwater pearl mussel (Margaritifera margaritifera) were analyzed by means of taphonomy and sclerochronology. The samples originated from two small rivers in northern Finland, River Kotioja and River Saukko-oja. Taphonomical analysis showed that the mussels died recently and that the shells were likely to be opened violently through(More)
Four regional Scots pine ring-width chronologies at the northern forest-limit, and in the northern, middle and southern boreal forest belts in Finland cover the last fourteen centuries. Tree-ring statistics and response functions were examined, and tree-ring width variation was also compared to North Atlantic Oscillation (NAO) and volcanic forcing. The(More)
This study investigates the climate impact on the radial increment of pedunculate oak (Quercus robur L.) in Estonia at the species’ northern distribution limit. Tree-ring width series of 162 living oaks were compiled into three regional chronologies—western (1646–2008), northeastern (1736–2011), and southeastern Estonia (1912–2011). Although these regional(More)
There have been great advances in the field of dendroclimatological research during the past decades. Tree-ring data have been used to derive various climate variables for certain localities and for larger regions. Characteristics of tree-rings provide measurements which can be used as records of climate variability prior to any instrumental weather(More)
Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other "Old World" climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have(More)
Radial growth of boreal tree species is only rarely studied in riparian habitats. Here we investigated chronologies of earlywood, latewood, and annual ring widths and blue intensity (BI; a surrogate to latewood density) from riparian lake shore and upland forest interior pines (Pinus sylvestris L.) growing in boreal forest in eastern Finland. Riparian and(More)
Shell morphometry, pre-mortal taphonomy and ontogeny-related growth characteristics of freshwater pearl mussel in northern Finland. — Ann. Zool. Fennici 44: 285–302. Museum collection of endangered freshwater pearl mussel (Margaritifera marga-ritifera) shells was studied. The ontogenetic ages of the mussels were estimated to be between 12 and 178 years.(More)
Our current knowledge on climate-mediated effects on human population dynamics is based on preindustrial agrarian societies where climate-induced crop failures had a major impact on fertility and mortality rates. However, because most of the human evolutionary history has been shaped by hunter-gatherer lifestyle relying on diverse plant and animal food(More)
The mortality of Scots pine trees in and around Helsinki has been reported in recent years, but the causalities of these deaths have not so far been rigorously examined. Tree-ring analyses have previously shown to effectively reveal historical growth variability and thus hint at the stress factors behind tree mortality. Here, we analyzed the tree rings of(More)