Spring warmth gave no clear change in the balance of lilac bloom intervals in four western US samples, 1961-2003

We tested whether spring warmth changed the time after full bloom relative to the time before full bloom in common lilac. Four separate region and period models used 7,465 complete plant-year reports from the historic western US program. Models controlled plant effects, year effects and January-February temperature. March-May slopes ranged from -0.13 to +0.45 days per C. All four family 95% intervals included zero. Checks changed the temperature window, report flags, long gaps and plant weights. The result does not establish that the effect is absent or small. Missing visits, few state clusters, selected records and coarse monthly temperatures limit inference. This study does not test air pollution or daily extremes. The package contains code, exact input panels, source hashes, all estimates and numerical checks.

phenology · common lilac · flowering intervals · spring temperature · observation bias · uncertainty