Historical phenological responses in apple to contrasting warming contexts may clarify future crucial responses in Europe

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitières; Phenological responses to warming in temperate fruit trees have rarely been investigated in contrasting warming contexts. This framework is appropriate for highlighting varying responses that would combine chill accumulation declines and heat accumulation increases. A comprehensive overview of historical responses might clarify crucial future responses in the warmest European regions. To examine this issue, a dataset was constituted in apple from flowering dates collected for main BBCH stages in contrasting temperate regions of Western Europe and in different mild regions (Northern Morocco, Southern Brazil). Multiple change-point models were applied to series of flowering date, flowering duration and temperature, aiming to statistically analyse both flowering responses and temperature changes. Modelling of flowering date was used to understand the determinisms of warming responses. In addition, regional differences in dormancy dynamic were characterized by forcing tests. Statistical analysis provided an overview of flowering date responses at global scale, highlighting flowering advances, mainly in Europe and Morocco, but also stationary flowering date series in Brazilian and French Mediterranean regions. Modelling analysis supported the notion that flowering advances are due to heat accumulation increases, explained by marked warming during ecodormancy. Later dormancy releases due to chill declines were also supported in Europe and may explain, in long term, stationary flowering dates in the French Mediterranean region. While the flowering duration series were stationary whatever the region, the flowering duration was far longer in Moroccan and Brazilian regions compared to European. This was linked to contrasting differences in dormancy dynamic observed between these mild and temperate regions. Dormancy release was inadequate in mild due to poor chill accumulation, leading to extended flowering durations. Since later dormancy releases would already have significant impacts on flowering date in Europe, new crucial warming responses, such as extended flowering durations, could be experienced especially in Mediterranean regions in near future.