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

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.

Funding We thank the Partnership for Research and Innovation in the Mediterranean Area (PRIMA), a program supported under H2020, the European Union’s Framework program for research and innovation, for funding this research within the AdaMedOr project (grant number 01DH20012 of the German Federal Ministry of Education and Research). We also thank national donors from the partner countries: the Spanish Ministry of Science and Innovation (Agencia Estatalde Investigación 10.13039/501100011033) and NextGeneration EU/PRTR (grants PCI2020-111966 and PID2020-115473RR-I00 in the case of CITA; grant PCI2020-112113 in the case of CEBAS); the Ministère de l’Enseignement Supérieure et de la Recherche Scientifique et de l’Innovation, Direction de la Recherche Scientifique et de l’Innovation(MENF-PESRS/DRSI- Maroc) in the case of Morocco; and the Tunisian Ministry of Higher Education and Scientific Research in the case of Tunisia. A. Picornell was supported by a postdoctoral grant financed by the University of Malaga for a research stay at the working group of Horticultural Sciences, Institute of Crop Science and Resource Conservation (INRES), University of Bonn, and by a postdoctoral grant financed by the Consejería de Transformación Económica, Industria, Conocimiento y Universidades (Junta de Andalucía, POSTDOC_21_00056)

agroclimatic requirements

dormancy

temperate fruit tree

Climate adaptation

Phenology

winter chill

Published