March warmth gave no clear common link to first-to-full cherry bloom intervals at 43 Japan stations in 1961-2020

We tested whether March warmth was linked to a shorter time from first cherry flowers to full bloom. We used 2,543 paired records at 43 fixed Japan stations in 1961-2020. Models controlled for winter temperature, station means and station-specific time trends. The pooled March slope was +0.18 days per degree C, with a 95 percent interval from -0.09 to +0.44. All four West and East, early and late intervals included zero after correction for four tests. First flowers and full bloom both came earlier with March warmth. Their estimated slopes were -3.24 and -3.06 days per degree C. Adding year effects gave an uncertain negative interval slope. These results do not show equal responses or a zero effect. Missing visits, tree changes, selected complete records, current coordinates and coarse monthly weather limit inference. March weather can extend past bloom. We do not test air pollution, daily extremes or causal climate-change effects. The package gives code, a paired data panel, raw source hashes, model checks and a figure.

phenology · cherry · temperature · Japan · observation bias · bloom interval