March warmth had positive links to the beech-minus-larch emergence gap in four Swiss samples in 1961-2020

We tested the link between monthly warmth and the gap from larch needle emergence to beech leaf unfolding. We used 4,450 matched station-years at 94 Swiss stations in two regions and two periods from 1961 to 2020. March slopes were +2.18 to +2.46 days per degree C. All four eight-test adjusted intervals were above zero. Stricter station coverage, station trends and short serial-dependence checks kept this result. April results were less stable. Independent date errors of three days per event permit either March slope sign in all four samples. These are retrospective associations, not causal climate effects or evidence of ecological harm. Missing visit logs, selected stations, shared climate and coarse monthly weather limit inference. The package gives code, paired evidence, source hashes, uncertainty, numerical checks and a figure. Pollution and daily extremes were not tested.

phenology · larch · beech · temperature · matched stations · observation bias · date uncertainty · Switzerland