Winter chill is a key determinant of cultivar adaptation in temperate fruit trees, and declining chill accumulation associated with climate warming increasingly challenges stone fruit production. This study evaluated whether cultivar-specific chill requirements explain performance across Prunus species and cultivars under contrasting Mediterranean climates. Two identical orchards were established in temperate Zaragoza and warm coastal Málaga, and endodormancy release was assessed over two seasons in eight early- and late-flowering cultivars of apricot, Japanese plum, peach, and sweet cherry. Sequential forcing of shoots was used to determine chill and heat requirements. Chill requirements ranged from 14.1 to 36.4 Chill Portions (CP) in early-flowering cultivars and from 27.7 to 55.0 CP in late-flowering cultivars, while heat requirements ranged from 4,839 to 11,003 Growing Degree Hours (GDH). At the temperate site, all cultivars released dormancy and flowered, whereas at the warm site responses were cultivar dependent and irregular, including weak or absent bud growth, low flower bud density, erratic flowering, and mortality of sweet cherry ‘Skeena’. Chill availability declined markedly at both locations. In Zaragoza, chill accumulation decreased from 81–85 CP in the 1980s to 73–80 CP in the 2020s and is projected to reach 50–65 CP by 2085 under SSP5. In Málaga, chill accumulation declined from 41–48 CP to 29–37 CP and is projected to approach near-zero levels by 2085 under SSP5. Thus, insufficient winter chill already constrains several stone fruit cultivars under warm Mediterranean conditions, highlighting the value of chill requirements for cultivar selection and adaptation planning.
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Fadón et al. (2026) studied this question.