Mean leaf colouring gaps showed no clear change among four tree species at 45 Swiss stations, 1996–2010 versus 2011–2025

We tested whether autumn dates became closer among four tree species at fixed Swiss stations. Open MeteoSwiss records gave 1,054 complete station-years for beech, birch, larch and rowan at 45 stations in 1996–2025. Each station had at least eight years with all four 50% colouring dates and all four 50% drop dates in each period. We compared 1996–2010 with 2011–2025 and gave stations equal weight. The mean absolute gap among colouring dates changed from 16.55 to 16.31 days. Its change was −0.24 days, with a nominal 95% interval of −2.02 to +1.24 days. We used shared three-year calendar blocks and 0.5-degree spatial groups in 4,999 bootstrap draws; 4,972 were valid. The mean drop-date gap changed by +0.51 days (−1.62 to +2.53). All planned coverage, time-block, spatial-group and species checks left the direction of colouring-gap change unresolved. A colouring-only set gave −1.28 days (−2.78 to +0.19), which shows sensitivity to the drop-data requirement. Mean colouring was 2.56 days later in the main set, but this delay was uncertain with stricter coverage. These records do not establish closer autumn dates or constant gaps. They do not measure leaf mass, carbon uptake or a climate cause. Independent source parsing and scalar calculations matched the selected records and main results. A clean offline rerun matched all generated files. The package contains raw data, source URLs and hashes, the local plan, code, estimates, bootstrap draws and figures.

autumn phenology · leaf colouring · leaf drop · species date gaps · Switzerland · MeteoSwiss · fixed station panel · shared year blocks · open data · null result