The mean leaf emergence delay fell, but the rise in reversed date order was uncertain for four species at 91 Swiss station pairs, 1961–1990 to 1996–2025

We tested whether a smaller elevation delay in leaf emergence came with more frequent reversed date order. We used open MeteoSwiss records for beech, hazel, larch and spruce. The main sample has 76 stations and 91 physical station pairs, with 247 species and pair combinations. Pairs were at most 30 km apart, differed by 200–800 m in elevation, and had at least 15 common years in each of 1961–1990 and 1996–2025. We gave species equal weight and pairs equal weight within species. The mean higher-minus-lower date gap fell from 13.01 to 10.69 days. Its change was −2.32 days, with a nominal 95% common-year block range of −3.60 to −1.02. The rate at which the higher station recorded emergence first rose from 17.65% to 19.18%. Its change of +1.53 percentage points had a range of −1.34 to +4.06. Thus, the main sample did not establish a clear rise in reversed order. Pairs up to 50 km apart and pairs with elevation gaps of 100–500 m gave clearer increases. A 20-year coverage rule gave an uncertain +0.28-point change. The result depends on the tested pair set. It does not prove stable order or identify a warming cause. Ranges condition on the selected stations and the year-resampling assumptions. Limits include missing dates, current station metadata, and unknown observer changes. The package preserves unchanged source data, all pair results, figures, resamples, code, source records and independent checks.

phenology · leaf emergence · elevation · date order · Switzerland · open data · reproducibility