Spring warmth gave no clear common link to residual lilac bloom spread in four US samples in 1965-2008

We tested whether local spring warmth changed residual spread in first-bloom dates. Four separate plant and year models used 9,015 US lilac records in two regions and two periods from 1965 to 2008. We removed a curved mean weather response and tested leverage-adjusted squared residuals. Spring slopes ranged from -0.792 to +3.999 days squared per C. All four main intervals included zero after correction for four tests. Flag removal gave a positive result only in early East. Three early western sensitivity fits had nonpositive two-way variance estimates. Wider additive variance checks are supplied. These records do not establish stable bloom spread. Missing visit schedules, selected long records, coarse weather, many plant effects, different lilac types and few state clusters limit inference. We do not test pollution, biological synchrony or causal climate-change effects. The package includes code, exact source hashes, a verified raw rebuild, the derived panel, all results and a figure.

phenology · lilac · residual spread · observation bias · temperature · null result