Previous summer warmth gave no clear change in spring bloom slopes in four US lilac samples in 1965-2008

We tested whether previous July-August warmth changed the link between March-April temperature and first bloom. Four US region and period models used 9,015 repeated lilac records in 1965-2008. Models had plant and year effects and a full quadratic seasonal temperature surface. Interaction estimates ranged from -0.782 to +0.238 days per C squared. All four intervals included zero after correction for four tests. Six sensitivity checks also gave uncertain interactions. This does not establish that the interaction is absent or small. Different plant types by region, selected long records, unknown visits, coarse weather, exposure overlap with bloom, and few state clusters limit inference. We do not measure pollution, extreme heat, or causal climate-change effects. The package includes input panels, a raw rebuild, source hashes, code, all results, numerical checks, and a figure.

phenology · lilac · seasonal interaction · previous summer · temperature · observation bias · null result