Spring warmth was linked to fewer first-bloom records after leaf reports in two US lilac samples in 1965-1986

We tested whether March-April warmth predicts an eligible first-bloom record when a first-leaf record is present in US lilac data. Four region-period models used 8,660 records from repeated plants, plant and year effects, and winter temperature control. In 1965-1986, eastern and western slopes were -2.47 and -2.60 percentage points per C. Four-test adjusted state-cluster intervals were -4.76 to -0.17 and -4.72 to -0.47. Two-way state and year intervals also stayed below zero, but the eastern upper limit was close to zero. Two 1987-2008 slopes were uncertain. Flag removal kept both early negative links. This is a conditional record-availability pattern. Missing visits, biological failure, archive handling and selection on leaf records cannot be separated. The result does not measure bias in bloom dates, a causal warming effect, or pollution effects. The package includes the raw-data build, exact panel, source hashes, all estimates, code, checks and figure.

phenology · lilac · observation bias · spring temperature · missing records · temporal replication