Matched maple and ginkgo records gave no clear difference in autumn interval trends at 31 Japan stations in 1953-2020

We tested whether the time from leaf colour to leaf fall changed at different rates in maple and ginkgo in Japan. We matched four event dates by station, year and reporting category. There were 1,481 matched station-years at 31 stations in 1953-2020. Equal-station-weight models controlled for station and reporting category. All six corrected intervals for the tree-type trend difference included zero in two regions and three time scopes. Full-record differences were +0.11 days per decade in the North and -0.51 in the South. The corrected intervals were -2.42 to +2.64 and -1.60 to +0.58. Temperature adjustment and station-ground record selection gave the same broad result. This does not establish equal trends or a shared cause. Five northern stations, selected complete records, unknown visits and tree changes limit inference. We do not identify pollution or causal climate-change effects. The package includes code, matched dates, climate values, source hashes, estimates, a figure and numerical and source checks.

autumn phenology · ginkgo · maple · matched records · observation bias · Japan · null result