Cherry phenology as bioindicator for climate change

Meteorological data over 60 years (1956-2015) from the University of Bonn, Campus Klein-Altendorf research centre's own weather station, were analysed for climate change effects. The error rate in the 18,000 temperature data was 0.77% and corrected where possible before digitising. Their analysis showed two distinct climate phases in Klein-Altendorf, an earlier 32-year-period (1956-1987) with a temperature of -0.5 degrees C below the long-term, 60-year average of 9.5 degrees C, followed by a 28-year-period of a +0.6 degrees C temperature rise (1988 to 2015). In addition, 30 years of phenological data, also on filing cards, included calendar dates of flower opening and full bloom, as well as late frost, for a range of cherry cultivars. This implied i) the use of several generations of cherry trees/orchards and ii) the use of the same original cherry cultivars, which existed as bearing trees and were replanted after the orchard had been removed. A comparison of available definitions of phenological stages previously used independently throughout Europe showed overlaps and shortcomings; hence, harmonisation was reached in this respect in the COST Cherry FA 1104 working group 2 based largely on the acceptance of the BBCH scale; similarly, cultivars to be monitored in future for phenology and climate change effects throughout Europe were agreed on for harmonisation. A comparison of the phenological data of the last 15 years (2002 to 2016) with earlier data (1978-1995) showed 4-5 days earlier flowering (F1) in 'Burlat' cherry, interpreted as a possible response to warmer spring temperatures.