Previous October warmth gave no clear common bloom delay in four US lilac samples in 1965-2008

We tested whether a warm October was linked to later lilac first bloom in the next year. We used 9,015 repeated records in four separate US region and period samples from 1965-2008. Models included plant and year effects and winter and spring weather. Previous-October slopes ranged from -0.501 to +0.348 days per C. All four adjusted intervals included zero. Future-October checks did not show a clear prior-minus-future difference in any sample. One future slope had a descriptive 95% interval above zero, but its four-test interval included zero. All planned sensitivity intervals for the previous-autumn slope included zero. The results do not show a common autumn delay. They do not establish a zero effect or test daily dormancy processes. Missing visit data, selected long records, different lilac types, coarse weather and few state clusters limit inference. The package includes source hashes, raw-data build code, the exact panel, all estimates, independent numerical checks and a figure.

phenology · lilac · autumn temperature · ecological timing · observation bias · regional replication · future exposure control · null result