April-May warmth was linked to shorter leaf-to-bloom intervals in four US shrub samples in 1961-2008

We tested whether seasonal temperature links to the time from first leaf to first bloom repeat across US regions and periods. A public archive gave 10,323 paired reporting-unit years for four cultivated shrub types in 1961-2008. Separate models for East and West and two periods included unit and year effects and January temperature. April-May slopes ranged from -1.56 to -1.95 days per degree C; all four marginal 95 percent state-and-year cluster intervals were below zero. February-March slopes were positive, but three of four intervals included zero. Flag removal and unit trends were checked. The observations overlap earlier campaign studies; this is an extension, not an independent archive replication. Monthly windows can follow events. Missing visits, selected long records, different species mixes and coarse weather prevent a causal climate interpretation. No pollution effect was tested. The package contains paired data, code, hashes, estimates, a figure and numerical checks.

phenology · seasonal temperature · leaf-to-bloom interval · observation bias · regional comparison · cultivated shrubs