Contrasting responses to climate change – predicting bloom of major temperate fruit tree species in the Mediterranean region and Central Europe
Lars Caspersen, Katja Schiffers, Antonio Picornell, José A. Egea, Álvaro Delgado, Adnane El Yaacoubi, Haïfa Benmoussa, Javier Rodrigo, Erica Fadón, Mehdi Ben Mimoun, Mohamed Ghrab, Ossama Kodad, David Ruiz, Eike Luedeling
Abstract
• Advancement in bloom of apple, pear, plum and sweet cherry are expected in next century in Central Europe. • Constant bloom of sweet apricot, sweet cherry and pear in northern Spain. • Delayed bloom of apple, almond, pistachio in southern Spain, Morocco and Tunisia. • Delays often coupled with increased risk of bloom failure. • Strong differences among 110 analyzed cultivars, especially for apricot and almond. Climate change is shifting the timing of leaf emergence and bloom in temperate-zone trees. While warming typically advances spring phenology, insufficient winter chill can delay or prevent bloom. Understanding species- and cultivar-specific responses is vital for adaptation planning. We calibrated the PhenoFlex phenology model using long-term bloom data for 110 cultivars of seven temperate fruit and nut tree species (apple, pear, apricot, sweet cherry, plum, almond, pistachio) across Spain, Tunisia, Morocco and Germany. The models projected bloom dates and potential bloom failure – when agroclimatic requirements are not met – under current (2015) and future scenarios for two time periods (2035–2065, 2070–2100) and four warming scenarios (SSP1–2.6, SSP2–4.5, SSP3–7.0, SSP5–8.5), using 14–18 General Circulation Models. Three key trends emerged: advancing bloom dates in Germany, delayed bloom for most species in southern Spain, Tunisia, and Morocco, and largely unchanged bloom dates in northern Spain and for almonds in Morocco. The contrasting shifts in bloom result from differences in the primary driver of bloom timing: heat where bloom advances, chill where bloom is delayed and chill and heat substitution where bloom is stationary. In the short term (2035–2065), agroclimatic requirements for most species are expected to be met, except for apricots in southern Spain and pistachios in central Tunisia. Predicted bloom failure rates spiked for most species in Tunisia, Morocco, and southern Spain under pessimistic warming scenarios in the long term (2070–2100) and, to a lesser extent, in northern Spain. Our results reveal cultivar-specific differences in bloom date shifts and failure rates, indicating variation among cultivars in their adaptability to winter warming. This information may guide the design of climate-resilient orchards based on cultivars’ alignments with projected agroclimatic conditions.