Spring warmth had no clear link to the elevation slope of the beech-hazel leaf date gap at 12 Swiss stations in 1981-2024

We tested whether March-April warmth changes the elevation slope of the beech-minus-hazel leaf unfolding gap. We used 528 paired station-years at 12 fixed Swiss stations in 1981-2024. Four region and period models controlled winter temperature and time. Spring estimates ranged from -2.56 to 3.44 days per km per degree C. All marginal and four-test intervals included zero. Station omissions changed some signs. Exact bounds under errors of up to one day per event permitted both signs in every sample. These data do not establish a repeated link or equal species responses. Few selected stations, a narrow elevation range, coarse weather and missing visit records limit inference. The package includes the evidence panel, code, provenance, figures and independent numerical checks.

phenology · beech · hazel · elevation · temperature · observation bias · null result · paired species