Reliable models of fruit tree flowering phenology that are stable across different climate conditions and
for a range of cultivars are required to better anticipate and adapt to anthropogenically induced climate
change. Two phenology models, the commonly applied sequential model and the newly defined chill
overlap model, were investigated to evaluate their ability to represent ‘Cripps Pink’ apple flowering
phenology data from a wide range of Australian climates. This is the first study to directly compare the
chill overlap and sequential phenology models and the first flowering phenology study of this spatial size
for apple in the Southern Hemisphere. The sequential model did not adequately explain the variability
in the dataset (RMSE 14.7 days) and was a worse approach than modelling to mean full bloom dayof-year
(RMSE 9.6 days). The chill overlap model fitted with a chilling requirement of 34 chill portions
was better able to represent the observations with RMSE of 6.9 and 5.8 days for parameterising and
validating datasets, respectively. Based on the results of this study, further exploration and application
of the chill overlap model is warranted, particularly in relation to climate impact assessments and for the
development of adaptation strategies.
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