Mean leaf emergence gaps showed no clear change at 28 Swiss stations from 1961–1990 to 1996–2025

We tested whether leaf and needle emergence dates became closer among four woody plant species at the same Swiss stations. We used open MeteoSwiss records for beech, hazel, larch and spruce. A fixed coverage rule selected 28 stations at 200–1,350 m, each with at least 20 complete four-species years in both 1961–1990 and 1996–2025. The comparison has 1,436 station-years. We averaged all six absolute species date gaps within each station-year and gave stations equal weight. The mean event date advanced by 6.73 days, with a nominal 95% interval of 3.18 to 10.10 days earlier. The mean species gap decreased from 15.73 to 14.93 days. Its change was −0.80 days, with an interval of −2.75 to +1.11 days from 9,999 station and shared five-year block draws. Three- and ten-year blocks and two other coverage rules also gave intervals that included zero. The records show earlier mean dates but do not establish closer dates among species. They do not establish constant gaps. The test concerns four station-level events, not direct plant interactions. The package contains source files, exact input hashes, code, figures, all estimates and independent checks. This local test through 2025 adds to prior European evidence; it makes no claim of a first general discovery.

plant phenology · leaf unfolding · MeteoSwiss · species date gaps · shared annual weather · open data · reproducibility · null result