Climatic signals extracted from ring-width chronologies of Scots pines from the northern, middle and southern parts of the boreal forest belt in Finland

Climatic signals were extracted from ring-width chronologies of Scots pines (Pinus sylvestris L.) from natural stands of the northern, middle, and sou thern parts of the boreal forest belt in Finland. The strength of the commo n growth signals (forcing factors) were quantified as a function of time. T his was achieved by mean inter-series correlations, calculated over a movin g 30-year window, both within and between the regional chronologies. Strong regional signals and also evidence for common forcings were found, especia lly between northern and central, central and eastern, as well as central/e astern and southern chronologies. Response function analyses revealed that growing season temperatures govern the growth rates of northern pines, whil e towards south, pine growth becomes less affected by temperatures, and mor e affected by e.g. precipitation. During some periods, growing conditions s eem to have been favorable in the south, while they have been unfavorable i n the north (growth inversions). Going from the north to the south, the var iability of radial growth clearly decreases, and the variance of ring-width series becomes smaller. Growth variability in the four regions was compare d during the common interval of the chronologies, from 1805 to 1991. The sp ectral densities of the northern, central, eastern and southern chronologie s were also compared as functions of frequency, viz. cycles per year. The v ariance is much greater and there is more periodic behavior in the north th an in the south in high, medium, as well as lower frequencies.