Performance of three numerical models to assess winter chill for fruit trees—a case study using cherry as model crop in Germany

Abstract

The Meckenheim fruit growing region in Western Germany may be affected as a consequence of climate change by lack of chilling, i.e. a cold period in the winter required for tree species to flower in the subsequent spring. As sweet cherry requires high chill, 160 potted trees of three sweet cherry cultivars with threefold different chilling requirements were cultivated in a large experiment over 4 years, either in the orchard or in an unheated greenhouse (simulated climate change). The orchard temperatures in the warmer winter (6.0 °C) exceeded those in the unheated greenhouse (4.7 °C) in the cold winter. Chilling computations for this region showed that cherry trees of low chill cultivar ‘6000CZ’ required 22.3–26.6 chill portions (CP), medium chill cv. ‘Brooks’ about 37.9–54.4 CP and the high chill cv. ‘Schneiders spate Knorpelkirsche’ about 54.4–79.3 CP for a natural flowering. Cherry trees cv. ‘6000CZ’ receiving <300 CH, cv. ‘Brooks’ <500 CH and cv. ‘Schneiders spate Knorpelkirsche’ <700 CH were unable to flower, equivalent of 50 % of the assumed chilling optimum of the respective cultivar. Maximum chill accumulation in this region is currently achieved, so that warmer winters may reduce the available chill. The beginning of leaf drop was identified as a suitable initiation point for computing chill accumulation. Overall, the work has shown that environmental change has an effect on chilling availability in Meckenheim and possibly other fruit growing regions along 50°N. The insights gained ultimately highlight the need for cross-sectoral, adaptive management practices that jointly target a sustainable regional development.