Warm January-February seasons were linked to wider plum-to-cherry flowering gaps in four Japan samples, 1953-2024

We tested whether seasonal warmth changes the gap between first plum and cherry flowers. We used 3,260 paired station-years at 48 Japan stations in 1953-2024. Models removed station means and a time trend and controlled March temperature. A degree C warmer January-February season was linked to a 6.58-day wider gap (95 percent interval 5.27 to 7.90). The link was positive in four separate East and West, early and late samples after correction for eight tests. Plum dates moved earlier more strongly than cherry dates. March slopes were negative but did not pass the corrected tests. The winter link remained positive with year effects, station trends, prior December adjustment, and on-site records. This is an observational result. Some weather occurred after plum flowering. Unknown visits, tree changes, selected long records and coarse weather limit inference. The study does not measure pollinator overlap, pollution, daily extremes or a causal climate-change effect. The package includes code, paired records, source hashes, numerical checks and figures.

phenology · plum · cherry · seasonal temperature · observation bias · Japan