Spring leaf dates gave no clear gain in 2016–2025 autumn predictions at 95 Swiss beech stations with observed weather

An earlier spring can come with earlier autumn leaf colouring. We tested whether this link improved later predictions in open MeteoSwiss records. At 95 European beech stations, we fitted linear models to 3,760 station-years in 1961–2015. Both models used station effects, a time trend and measured seasonal weather. One also used the spring leaf-unfolding date. The historical spring coefficient was +0.157 autumn days per spring day (95% interval +0.045 to +0.270). In 849 station-years in 2016–2025, prediction RMSE changed from 11.177 to 11.246 days when spring was added. The change was +0.069 days, with a conditional bootstrap interval of −0.106 to +0.268. The later spring coefficient was −0.007 (−0.077 to +0.063). Eight other tree species also gave no clear prediction gain. Planned model and panel checks gave the same conclusion for beech. The models use observed weather in each test year. This is a conditional prediction test, not a forecast made in spring or a causal test of tree physiology. The package preserves source data, provenance, code, predictions and figures.

phenology · European beech · leaf unfolding · leaf colouring · MeteoSwiss · temporal validation · conditional prediction · autumn