Abstract
Abstract. Growing trees are quite vulnerable to cold temperatures. To minimise the effect of these cold temperatures, they stop their growth over the coldest months of the year, a state called dormancy. In particular, endodormancy requires accumulating chilling temperatures to finish this sort of dormancy. The accumulation of cool temperatures according to specific rules is called chilling accumulation, and each tree species and variety has specific chilling requirements for correct plant development. Under global warming, it is expected that the fulfilment of the chilling requirements to break dormancy in fruit trees could be compromised. In this study, the impact of climate change on the chilling accumulation over peninsular Spain and the Balearic Islands was assessed. For this purpose, bias-adjusted results of 10 regional climate models (RCMs) under Representative Concentration Pathways (RCPs) 4.5 and 8.5 were used as inputs of four different models for calculating chilling accumulation, and the results for each model were individually compared for the 2021–2050 and 2071–2100 future periods under both RCPs. These results project a generalised reduction in chilling accumulation regardless of the RCP, future period or chilling calculation model used, with higher reductions for the 2071–2100 period and the RCP8.5 scenario. The projected winter chill decrease may threaten the viability of some tree crops and varieties in some areas where the crop is currently grown, but also shows scope for varieties with lower chilling requirements. The results are relevant for planning future tree plantations under climate change, supporting adaptation of spatial distribution of tree crops and varieties in Spain.
Highlights
Growing fruit trees is an important source of income for farmers
Chilling units calculated with the four chilling models for every CORDEX cell with Spain02 (Fig. 3a) and with the EUR-11 ensemble (Fig. 3b) were in good agreement (Fig. 3c), with mean absolute percentage error (MAPE) chilling values based on EUR-11 compared to those based on Spain02 generally lower than 5 %
MAPE values were higher than 20 % only for some coastal or mountainous regions
Summary
Growing fruit trees is an important source of income for farmers. Spain is one of the largest producers of fruits and vegetables in Europe, with EUR 7.437 billion from 7.4 million tonnes of exported fruits in 2017 (FEPEX, 2018) from a total fruit production of 23.17 million tonnes (MAPA, 2018). Among fruit crops olive trees occupy the largest land area (2.52 million hectares), followed by vineyard (0.94 million hectares), almond (0.58 million hectares), citrus (0.26 million hectares) and peach trees (0.09 million hectares). One of the most important groups of fruit trees are the temperate trees, accounting for approximately 48 % of the total world fruit production according to FAOSTAT (2018). In Spain, fruit trees are concentrated mainly on the east coast, along the river valleys of the coast, especially in the Ebro and Júcar valleys; apples are found mainly in the north-west and northeast of Spain and peaches are found mainly in the north-east and south-east of Spain. Olive trees are concentrated in the south of Spain, especially in the Guadalquivir River valley. Vineyards have a more diffused distribution but are abundant in central Spain (Fig. 1)
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