Climate change and shifts in dormancy release for deciduous fruit crops in Germany

Four different chilling models, the Weinberger-Eggert model (C1), Utah model (C2), Positive Utah model (C3), and Dynamic model (C4), were used to evaluate possible future changes in the date of dormancy release (t(1)) in Germany for deciduous fruit crops with a chilling requirement (C*) ranging from 700 to 1800 chill units. The study was based on gridded air temperature data in a 7 x 11 km horizontal resolution for current and future climate conditions. Currently, dormancy of low chill crops, up to similar to 1000 chill units, is released evenly across Germany. However, for high chill cultivars (1500 to 1800 chill units) the chilling fulfillment occurs later in the colder continental, SE areas than in the mild, maritime NW regions of Germany. For future climate conditions (2071 to 2100), the patterns of t(1) will change, depending on the regional temperature rise. As a result, the areas which currently have a late date of dormancy release could have an advanced date in the future and vice versa, reducing the current differences between the northern and southern areas. Among the models, we found some different results. Model C1 showed a delay of t(1) for all values of C*. The other chilling models (C2-C4), showed a delay in t(1) for low chill varieties (700 to 1000 chill units), only small changes for medium chill varieties (1100 to 1400 chill units), and an earlier timing in the end of winter dormancy for fruit crops with a high C* (1500 to 1800 chill units). If we follow the results of these 3 models, we conclude that dormancy in a wide range of deciduous fruit crops in Germany will be released early enough to ensure a timely start of reproductive development in the future.