Swiss spring plant phenology 2007: Extremes, a multi-century perspective, and changes in temperature sensitivity

Spring (March-May) 2007 was characterized by record high temperatures over European land areas. Anomalously high temperatures led to a very early onset of plant phenological spring phases, including 98 record early observations out of a possible total of 302 (32%) for selected phases in Switzerland. In the context of the last 300 years and based on three tree species, 2007 marks the third earliest, after 1961 and 1794, plant phenological spring onset in Switzerland. We show that the temperature sensitivity of Swiss plant phenology to spring temperatures has changed within the last three centuries: sensitivity has generally increased over the record period but also decreased during two periods with warming trends (1890-1950; 1970-2007).