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Climate warming causes phenological shifts and intensifies drought for trees at lower elevations

Lay summary of the following paper: Meier, M., Y. Vitasse, H. Bugmann, and C. Bigler. 2021. Phenological shifts induced by climate change amplify drought for broad-leaved trees at low elevations in Switzerland. Agricultural and Forest Meteorology 307:108485.

Autumn leaf coloration of beech tree
Image: C.Bigler

The timing of leaf unfolding and colouring of trees in Switzerland is known to have shifted in due to climate warming: Today, leaf unfolding mainly occurs earlier, whereas leaf colouring occurs earlier or later, depending on bioclimatic conditions during the growing period and other influencing factors. These shifts change the timing and length of the growing period. As a result, certain days are included in or excluded from the growing period, which in turn affects the corresponding bioclimatic conditions. This study examined past trends in bioclimatic conditions during the growing period. In addition, the authors quantified the influence of shifts in leaf unfolding and colouring on these trends. These shifts led to a lengthening of the growing period for beech, rowan, sycamore and larch. Corresponding trends since 1985 were strongly dependent on elevation and reached +6.1 days/decade. In addition, climate warming led to a predominant decrease in precipitation during the growing period. Consequently, the corresponding drought intensity increased for beech, rowan, sycamore and larch. Shifts in leaf unfolding and colouring amplified the trends towards drier conditions at low elevations for beech, rowan and sycamore, but weakened them at high elevations for beech, rowan, sycamore and larch.