Wood anemone flowering and beech leaf opening occurred earlier at 54 Swiss stations; their gap change was uncertain, 1961–1990 versus 1996–2025

We tested the date gap between 50% wood anemone flowering and 50% beech leaf unfolding in open Swiss records. The fixed set has 2,644 paired station-years at 54 stations, with at least 15 paired years per station in both 1961–1990 and 1996–2025. We gave each station equal weight. Flowering occurred 9.97 days earlier and leaf unfolding occurred 5.47 days earlier in the later period. The mean beech-minus-anemone gap increased from 23.25 to 27.75 days. Its change was +4.50 days. The planned spatial-cell and common five-year-block resampling gave a nominal 95% interval of +0.09 to +9.13 days from 4,999 draws. Because the lower bound was near zero, we added a 49,999-draw check. Its interval was −0.01 to +9.12 days. Several planned coverage and median checks also included zero. Both events occurred earlier, but the records did not establish a clear direction of gap change. They did not establish a constant gap. Station pairing does not prove a shared forest patch. Flowering and leaf unfolding do not measure canopy light, plant carbon gain, or a climate cause. The package has unchanged source data, direct source URLs and hashes, the plan, code, all results and draws, figures, independent checks, and offline repeat instructions.

phenology · wood anemone · European beech · Switzerland · paired observations · ecological change · uncertainty · open data