Matched US shrub records gave no clear species difference in seasonal leaf-to-bloom slopes in 1968-2004

We tested species differences in the seasonal temperature slopes of the time from first leaf to first bloom. We matched US shrubs by site, program and year. The main Arnold Red honeysuckle minus cloned lilac sample had 280 matched years at 23 eastern sites in 1971-2004. Its January-February and March-April slope differences were -0.44 and -0.24 days per degree C; both 95% intervals included zero. A secondary Arnold Red minus Zabeli sample had 1,468 matched years at 120 sites in 1968-2004. Its slope differences were -0.15 [-0.34, 0.05] and -0.16 [-0.51, 0.20] days per degree C. Region and period checks did not establish a common difference. Matching reduces shared site and observation effects but cannot remove species-specific reporting bias. Missing visits, selected complete records, coarse monthly weather and limited eastern coverage prevent causal or equality claims. The package includes matched records, source events, code, hashes, estimates and numerical checks.

phenology · matched species · observation bias · seasonal temperature · lilac · honeysuckle · null result