Latitude had a clear link to lilac spring sensitivity in one of four plant and year models for US records in 1965-2008

We tested whether first lilac bloom had a weaker response to spring warmth farther north. Four models used 9,015 plant-years in eastern and western US samples in 1965-1986 and 1987-2008. We controlled plant and year differences, winter warmth, winter sensitivity by latitude, and a latitude trend. Latitude interactions were +2.570, +0.874, +0.622 and +0.301 days per C per five degrees north. Only the early eastern interval was above zero after correction for four tests: +1.030 to +4.110. Adding a control for usual spring climate reduced that estimate to +0.892, with an interval of -1.230 to +3.014. A check on the same plants in both periods kept the one clear and three uncertain results. These data did not establish a clear common latitude relation separate from local climate. Different lilac types, changing site coverage, unknown visits, coarse seasonal weather, and few clusters limit inference. This is an ecological timing study. It does not test pollution, daily extremes, genetic adaptation, or a causal climate-change effect. The package includes the source recipe, measured hashes, selected panel, code, all results, numerical checks, and a figure.

phenology · lilac · temperature sensitivity · latitude · observation bias · regional replication · local climate