The mean gap from wood anemone flowering to beech leaf unfolding was 4.5 days larger at 54 Swiss stations in 1996–2025 than in 1961–1990

We tested whether the recorded date gap between wood anemone 50% flowering and beech 50% leaf unfolding changed. We used open MeteoSwiss records at 54 fixed stations with at least 15 paired years in each period. We compared 1961–1990 with 1996–2025 and gave stations equal weight. The 2,644 paired records gave a mean gap of 23.25 days in the early period and 27.75 days in the late period. Anemone flowering moved 9.97 days earlier; beech unfolding moved 5.47 days earlier. The gap change was +4.50 days. Its 95% common five-year-block range was +0.42 to +8.62 days with stations fixed. The range was −0.11 to +9.14 days when spatial groups were also sampled. The gap increased at 39 stations. Coverage rules and equal year weights kept the mean change positive. Shorter and recent periods gave uncertain changes. The two events need not come from one forest stand. Their gap does not measure light, plant carbon uptake or a climate cause. The package has unchanged source CSV files, source URLs and hashes, code, all results, figures and independent checks. A clean offline replay reproduced the numerical results and both figures.

phenology · wood anemone · European beech · Switzerland · species timing · open data · paired dates · reproducibility