The time from leaf colour to leaf fall decreased in three of four Japan samples in 1953-2020

We tested trends in the time from leaf colour to leaf fall in Japan in 1953-2020. We used 5,743 paired records for ginkgo and maple at 61 distinct stations. Models gave equal total weight to each station and controlled for station and reporting category. The four trends ranged from -0.97 to -1.59 days per decade. Intervals with a four-test correction were below zero for ginkgo in both regions and maple in the South. The northern maple interval included zero. Seasonal temperature adjustment gave similar estimates. All eight half-period estimates were negative, but six corrected intervals included zero. The full-record change came from a larger delay in colour than in leaf fall. A check with separate reporting segments gave the same three clear full-record trends. Stable-category checks supported the two southern trends, but had few northern stations. These data show a change in late visible autumn stages. They do not identify its cause. Missing visits, tree replacement, incomplete records and shared observation methods limit inference. We did not test air pollution, daily weather extremes or wild population change.

autumn phenology · leaf fall · ginkgo · maple · observation bias · Japan · time trends