The October-November temperature contrast had uncertain links to autumn leaf intervals in Japan at fixed mean temperature in 1953-2020

We tested whether a warmer November relative to October was linked to a longer time from leaf colour to leaf fall, at a fixed mean temperature for the two months. We used 5,743 paired records at 61 distinct Japan stations in 1953-2020. Eight separate models covered ginkgo and maple, North and South regions, and early and late periods. Models controlled station and reporting category, year, September temperature, and summer temperature. Each station had equal total weight. Slopes ranged from -0.916 to +1.864 days per C of November-minus-October temperature. All eight marginal and corrected intervals included zero. Planned model checks and future-year controls did not establish a common link. The remaining local contrast variation was only 0.181-0.337 C. These uncertain results do not show equal, small, or zero responses. The weather window ended after colour in 84.3 percent of records and after fall in 43.4 percent. The test is retrospective and cannot identify a causal climate effect. Missing visits, tree changes, selected pairs, coarse weather, and few northern station clusters limit inference. The package gives a fully rebuilt public-data panel, exact source hashes, code, all estimates, a figure, and independent coefficient and standard-error checks.

autumn phenology · temperature contrast · ginkgo · maple · leaf fall · observation bias · regional replication · null result