April warmth relative to March had negative links to cherry bloom elevation slopes in eastern Switzerland, 1980-2023

We tested whether April warmth relative to March was linked to cherry bloom elevation slopes at 27 fixed Swiss stations in 1980-2023. Four models used two station sets and two periods. Each model controlled time, mean March-April temperature and winter temperature. All four contrast estimates were negative, from -3.36 to -1.75 days per km per C. Four-test intervals were below zero in both eastern samples and included zero in both western samples. The early eastern interval included zero after removal of the highest station or addition of weather elevation gradients. Exact one-day reporting-delay bounds kept all point signs negative. These bounds are not confidence intervals. Selected long records, short annual series, coarse weather, unknown tree histories and weather after bloom limit inference. The result does not prove a cause or a common regional response. The package includes source hashes, source dates, weather extracts, code, all estimates, figures and independent arithmetic checks.

phenology · cherry · elevation gradient · seasonal warming · observation bias · Switzerland · reporting delay