Climate change and shifts in spring phenology of three horticultural woody perennials in northeastern USA

We evaluated spring phenology changes from 1965 to 2001 in northeastern USA utilizing a unique data set from 72 locations with genetically identical lilac plants (Syringa chinensis, clone Red Rothomagensis). We also utilized a previously validated lilac-honeysuckle spring index model to reconstruct a more complete record of first leaf date (FLD) and first flower date (FFD) for the region from historical weather data. In addition, we examined mid-bloom dates for apple (Malus domestica) and grape (Vitis vinifera) collected at several sites in the region during approximately the same time period. Almost all lilac sites with significant linear trends for FLD or FFD versus year had negative slopes (advanced development). Regression analysis of pooled data for the 72 sites indicated an advance of –0.092 day/year for FFD (P=0.003). The slope for FLD was also negative (–0.048 day/year), but not significant (P=0.234). The simulated data from the spring index model, which relies on local daily temperature records, indicated highly significant (P<0.001) negative slopes of –0.210 and –0.123 day/year for FLD and FFD, respectively. Data collected for apple and grape also indicated advance spring development, with slopes for mid-bloom date versus year of –0.20 day/year (P=0.01) and –0.146 (P=0.14), respectively. Collectively, these results indicate an advance in spring phenology ranging from 2 to 8 days for these woody perennials in northeastern USA for the period 1965 to 2001, qualitatively consistent with a warming trend, and consistent with phenology shifts reported for other mid- and high-latitude regions.