Contrasting Responses to Climate Change – Predicting Bloom of Major Temperate Fruit Tree Species in the Mediterranean Region and Central Europe

Abstract

One common manifestation of climate change is advancing leaf emergence and bloom in temperate-zone trees. However, under conditions where warming winters compromise the trees’ ability to fulfill their chilling requirements, spring phenology may instead be delayed. In severe cases, certain development stages, such as bloom, may not be fully reached. Understanding how particular tree species or cultivars respond to warming is crucial for adaptation planning but producing accurate predictions has proven difficult. We addressed this challenge by calibrating the novel PhenoFlex phenology modeling framework with long-term bloom data for 110 cultivars of seven temperate fruit and nut tree species (apple, pear, apricot, sweet cherry, plum, almond, pistachio), from Spain, Tunisia, Morocco, and Germany. We used the resulting models to project bloom dates and potential bloom failure – when agroclimatic requirements for flowering are not met – for current conditions and future scenarios for two time periods (2035–2065, 2070–2100), four warming scenarios (SSP126, SSP245, SSP370, SSP585) and multiple global circulation models for six study locations across four countries. We identified three general trends: advancing bloom dates for all species in Germany, delayed bloom 36 for most species in southern Spain, Tunisia, and Morocco, and largely unchanged bloom dates in northern Spain and for almonds in Morocco. 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 revealed cultivar-specific differences in bloom date shifts and failure rates, indicating variation among cultivars in their adaptability to winter warming. These information may guide the design of climate-resilient orchards based on cultivars aligned with projected agroclimatic conditions.