Local spring warmth had uncertain links to lilac bloom gaps in four US samples in 1965-1994

We tested whether warmer local springs were linked to smaller first-bloom gaps between fixed lilac sites. We used 2,109 pair-years in 198 selected pair series in the US East and West, split into 1965-1979 and 1980-1994. Models included pair and year effects and the temperature difference between endpoints. Mean-warmth slopes ranged from +0.067 to +1.085 days of gap per C. All four intervals included zero after correction for four tests. Their full range was -2.042 to +3.057 days/C. Seven planned sensitivity models did not establish a clear link in all samples. Some individual intervals supported wider gaps in the early East. The primary test uses local warmth relative to region-year weather. It does not estimate the effect of region-wide warming. Missing visit histories, selected long records, coarse monthly temperature, different lilac types, and 15 years per sample limit inference. The package has raw-source hashes and retrieval instructions, derived data, code, all results, numerical checks, and figures.

phenology · lilac · first bloom · spatial timing · spring temperature · observation bias · fixed pairs · regional tests · uncertainty