Dependence of tree-ring, earlywood and latewood indices of Scots pine and Norway spruce on climatic factors in eastern Finland

First, mixed linear models were utilised to predict growth index series related to climate. The indexed series were predicted for the whole tree-ring, earlywood and latewood of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) in eastern Finland. The ratio of latewood and earlywood indices was also calculated. Second, autoregressive moving average and transfer function modelling were used to evaluate the influence of monthly climatic data (input series) on the index series (output series) during 1910–1989. The index series were filtered with a first-order autoregressive or moving average model because only the latewood/earlywood ratio for Scots pine was a white noise series. The summer temperature of the current year was positively correlated with the indices of Scots pine, except with the earlywood indices, which correlated positively with precipitation in May. Precipitation in the previous summer had a positive influence on all Scots pine index series. All growth indices of Norway spruce were related positively to temperature of the current growing season and negatively to temperatures of the previous July and August. In Scots pine the latewood/earlywood ratio increased with high temperatures in the spring and late summer. In Norway spruce mild winters and high spring and low June temperatures increased the latewood/earlywood ratio.