| Summary: | A severe frost event in the winter of 1986/1987 that resulted in widespread defoliation in northern Finland was used to test the influence of such growth disturbances on tree ring parameters commonly used for palaeoclimate reconstruction. In mature pine trees there was no effect on ring widths, latewood densities or on stable carbon isotope ratios. In young trees, however, the effect was immediate and prolonged, with a measurable increase in water stress for two years and a suppression of ring widths lasting for 6 to 7 years. There was no effect on latewood density. Where pine tree ring chronologies are used to reconstruct summer temperatures, the common practice of ignoring the juvenile years should ensure that severe frost events do not bias the reconstructions. However, extreme events may be important for understanding changes in forest dynamics, and changes in the magnitude, and frequency of such events may be important signals of human impact. The sensitivity of young pines makes them a potential archive for reconstructing past changes in growth disturbance events such as severe ground frosts.
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