Same-year and following-year spring slopes did not clearly differ for beech autumn dates in four Swiss samples, 1961-2020

We compared the links of beech autumn leaf colouring with spring leaf unfolding in the same year and the following year. We used 3,165 complete annual records at 67 Swiss stations in western and eastern sets in 1961-1990 and 1991-2020. Four models had station and year effects, local seasonal temperature controls and equal total weight for each year. Same-year minus following-year slopes were 0.031, 0.115, -0.054 and -0.004 autumn days per spring day. All marginal 95 percent intervals and all four-test intervals included zero. The data did not clearly favour a larger same-year slope. This does not show equal slopes or rule out biological carryover. Missing visits, date error, selected long records, coarse weather and possible autumn-to-next-spring effects limit interpretation. The package gives code, source hashes, aggregate results, a figure and an independent numerical audit. External record-level data are not bundled.

phenology · European beech · seasonal carryover · observation bias · Switzerland · null result · temperature