Thermal requirements and climate trends of Japanese plum (Prunus salicina Lindl.) in the main producing regions of Spain

Spain is one of the leading plum-producing countries in Europe, contributing approximately 30% of total continental production. Spanish plum production is characterized by a wide range of high-quality cultivars, including Claudia, Golden Japan and Reina Claudia Verde. Other major plum-producing countries in Europe include France, Italy, Poland and Romania.

The main objectives of this study are to: (i) characterize the thermal requirements of the vegetative cycles of early-, mid- and late-season Japanese plum (Prunus salicina) varieties cultivated in the main producing regions of Spain; (ii) compare the principal growing areas from an agroclimatic perspective; and (iii) assess temporal trends in key bioclimatic indices across these regions.

The analysis was based on the period 1981–2024 and included the following variables: frost-free period, start and end dates of the vegetative cycle, number of days with optimal temperatures for growth and ripening, thermal integral of the crop cycle and ripening phase, as well as their associated trends.

The results reveal pronounced agroclimatic differences among producing regions, particularly between Seville and Valencia. These areas exhibit the longest frost-free periods, earlier flowering dates across all varietal groups, and shorter ripening phases for early varieties. Valencia records the highest number of days with optimal temperatures for plum cultivation, whereas Seville presents the highest mean temperatures throughout the crop cycle for all varietal groups. Marked differences in accumulated growing degree days were observed, strongly conditioning varietal suitability to regional agroclimatic conditions. In this context, Seville (4204 °C·day) and Murcia (4025 °C·day) show the highest thermal integrals, favouring earlier ripening compared to other regions and indicating a higher suitability for extra-early varieties. All studied regions exhibit highly significant increasing trends, reflecting a general warming of plum-growing areas, with the strongest increase detected in Murcia, reaching 22.9 °C·day·yr⁻¹ for late-cycle varieties.