Trade-off between height growth and spring flushing in common beech (Fagus sylvatica L.)

Introduction The annual development cycle of boreal and temperate trees results from an evolutionary trade-off between two opposing forces. These are namely, the adjustment of leaf phenology to the timing of frost occurrence at the beginning and/or the end of the growth season countered by an effective adjustment to the duration of the growth season to maximise photosynthesis and biomass production during the growing season. Objectives In a provenance trial of common beech (Fagus sylvatica L.) populations, we tested whether avoiding frost events by late flushing is the primary process of frost tolerance, and also, whether longer growth seasons resulted in an increase in biomass production. Results We detected clines with altitude and longitude of provenances for phenological traits, in contrast to growth variables. A highly significant negative genetic correlation was detected between frost damage and budburst date which confirms that the timing of leaf flushing is the principal determinant of tolerance to late frost. Height and diameter growth were positively correlated with the length of the vegetation season. However, this effect was associated with the timing of growth cessation rather than with budburst. Conclusions Stabilizing selection, selective pressure on early leaf flushing of juveniles in dense natural beech stands, and epigenetic regulation of budburst are proposed as explanations for these observations.