Previous spring warmth gave no clear link to lilac bloom dates in four US samples in 1965-2008

We tested whether previous March-April warmth was linked to current lilac first bloom after current winter and spring controls. Four US region and period samples used 9,015 repeated records in 1965-2008, with plant and year effects. Previous-spring slopes ranged from -1.030 to +0.074 days per C. All four intervals included zero after correction for four tests. Next-spring diagnostic slopes and lag-minus-lead differences were also uncertain. Plant trends, flag removal, curved current weather, lead removal and adjacent-year differences gave the same broad result. This does not exclude plant memory. Selected sites, unknown visits, coarse weather, different plant types by region and few state clusters limit inference. We do not test air pollution, community diversity or causal climate-change effects. The package includes code, the derived panel, selected weather, exact source hashes, a raw rebuild check, numerical validation and a figure.

phenology · lilac · climate memory · previous spring · observation bias · null result