Spring warmth gave no clear link to missing beech leaf-out records in four Swiss samples, 1961-2020

We tested whether March-April warmth predicts absent beech leaf-out dates in Swiss station-years with a recorded autumn leaf-colour date. Four samples cover two regions and two periods from 1961 to 2020. Of 5,272 station-years, 158 lack a spring date. After station and linear time controls, slopes range from -0.21 to +0.31 percentage points per C. All four 95 percent family intervals include zero. Stricter record coverage, quadratic time trends and station-specific trends also give no clear link. The result concerns selected years with autumn records. It does not prove random missingness or measure bias in climate response estimates. Missing visit histories, coarse weather and thirty years per sample limit inference. Code, source hashes, retrieval instructions, aggregate results and a static figure are included. External raw and record-level data are not bundled.

phenology · observation bias · missing data · beech · spring temperature · Switzerland