Abstract
Winter chill accumulation plays a crucial role in determining the moment of bud burst in temperate fruit and nut trees, and insufficient chill can greatly limit yield potentials. To assess future cultivation options for such species in South America, we estimated winter chill through a spatial analysis. We used historical data (1980–2017) from 158 weather stations to calibrate a weather generator and produce temperature data for 10 historical and 60 future scenarios. We computed Safe Winter Chill (SWC, corresponding to the 10th quantile of a chill distribution) for the period 1980–2017 and for all historical and future weather scenarios and developed a framework to interpolate SWC for the continent using the Kriging method. To improve the interpolation, we applied a 3D correction model based on two co-variables (means of daily temperature extremes in July). Our results suggest important chill declines in southern Brazil and central Chile. By 2050 under the global warming scenario RCP4.5 (Representative Concentration Pathway), absolute SWC in these regions may reach a median of 18.7 and 39.6 Chill Portions (CP), respectively. Projections are most alarming for a strong global warming scenario (RCP8.5). In southern South America, adequate SWC levels of about 60 CP may be expected even under the RCP8.5 scenario. Our results highlight the need for climate change adaptation measures to secure temperate fruit production in important growing regions of South America. The procedure we developed may help farmers and practitioners across South America estimate future SWC to adapt their orchards to future challenges.
Highlights
Woody species that evolved in temperate climate regions enter a dormancy phase in winter that allows these plants to withstand cold and freezing temperatures
Regarding future chill levels computed across the 15 General Circulation Models (GCMs), we summarized the Safe Winter Chill values according to ‘optimistic’, ‘intermediate’, and ‘pessimistic’ GCM projections
The results of our analysis suggest that the means of daily minimum and maximum temperatures in July may serve as the best predictors of winter chill accumulation in South America when compared with elevation and distance from the ocean (Fig. S3)
Summary
Woody species that evolved in temperate climate regions enter a dormancy phase in winter that allows these plants to withstand cold and freezing temperatures. Temperate species determine the right moment to overcome dormancy by sensing and recording the duration of cold (chilling period) and warm conditions (forcing period) throughout winter (see Fadón et al 2020a for a review). Once these species have experienced a certain period under both chilling and forcing conditions (meeting their chill and heat requirements—CR and HR, respectively), dormancy is broken and meristems resume growth (Campoy et al 2011; Fadón et al 2020a; Saure 1985; Vegis 1964). Knowledge of current and future chill levels in places where such species are cultivated may support farmers and orchard managers in making appropriate decisions to secure temperate fruit production in a warming climate
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