Four US lilac samples did not establish a common leaf-to-bloom link to March-April temperature contrast in 1961-2008

We tested the link between April minus March temperature and the time from first leaf to first bloom in repeated US lilac records. Models controlled plant and year effects, mean March-April temperature, and mean January-February temperature. Four region and period samples gave slopes from -1.17 to 0.71 days per degree Celsius of contrast. 1 of four confidence intervals excluded zero after correction for four tests. The later western interval included zero under a five-year record rule and a wider covariance method. The saved results separate leaf and bloom slopes on the same paired records. This is an observational replication and extension of earlier campaign work. Fixed monthly windows can extend past events. Missing visits, selected paired records, changing observation rules, plant types that differ by region, and coarse weather limit inference. The result does not measure pollution effects or attribute change to climate change.

phenology · lilac · seasonal temperature · paired events · observation bias · replication