Autumn warmth had uncertain links to the gap between maple and ginkgo colour dates in four Japan samples from 1953 to 2020

We tested whether September-October warmth changed the gap between maple and ginkgo leaf colour dates at the same Japan station. Four separate North and South, early and late models used 2,415 paired station-years at 45 stations in 1953-2020. Models removed station and reporting-category effects and shared year effects, with spring and summer temperature controls. Slopes ranged from -2.99 to +5.77 days per C. All four marginal and corrected intervals included zero. Station trends, month windows, record length and location checks did not establish a common change. A constant-category check had no northern stations. These results do not show equal responses or a zero effect. Missing visits, tree changes, selected long records, coarse weather and weak local weather variation limit inference. Fixed weather windows extended past some colour dates. This is a seasonal association test, not a causal climate-change or pollution test. The package includes a paired panel, source tables, exact raw hashes, code, figures, independent numerical checks and offline reproduction instructions.

autumn phenology · maple · ginkgo · relative timing · temperature · observation bias · Japan · paired records