2.3 Tree core sampling and processing
Following inventory, a sample of trees was selected for tree coring. InPicea plots, a subset of 25 trees per plot were selected for tree core extraction. If plots contained less than 25 trees, all trees were cored. In Fagus plots, all trees over 20cm dbh were cored and 1 in 4 trees in the 10-20 cm dbh class were cored, and all trees within a central 5m-radius subplot were cored. One core was extracted from each tree at 1 m above ground level and on the upslope side of the trunk. Only trees with more than 20 years of data were used and only plots with 5 or more trees were included. This yielded a dataset comprising 22209 trees within 813 inventory plots.
Tree cores were air-dried, then mounted on wooden boards and sanded until annual growth rings were made clearly visible. Following this, samples were cross-dated visually using extreme growth years (Yamaguchi, 1991). Annual ring widths were then measured using a stereomicroscope and a Lintabâ„¢ sliding-stage measuring station in conjunction with TSAP-WinTM software (Rinntech, Heidelberg, Germany). Cross-dating was subsequently validated using the programs COFECHA (Holmes 1983) and CDendro (Larsson, 2015).