Spring phenology trends in Alberta, Canada: links to ocean temperature

Warmer winter and spring temperatures have been noted over the last century in Western Canada. Earlier spring plant development in recent decades has been reported for Europe, but not for North America. The first-bloom dates for Edmonton, Alberta, were extracted from four historical data sets, and a spring flowering index showed progressively earlier development. For Popul us tremuloides, a linear trend shows a 26-day shift to earlier blooming ove r the last century. The spring flowering index correlates with the incidenc e of El Nino events and with Pacific sea-surface temperatures.