Dealing with Increased Variability of Spring Temperatures in Temperate Deciduous Orchard Crops

Abstract

Productivity of temperate deciduous crops is potentially more vulnerable to climate change than many annual crops because temperate deciduous crops flower and set crops at the beginning of the growing season when temperatures vary greatly. The fruit development periods (time between bloom and harvest) of many fruit tree species (peach and nectarine (Prunus persica), plum (Prunus salicina), prune (Prunus domestica), sweet cherry (Prunus avium), almond (Prunus dulcis), pear (Pyrus communis)) are inversely related to accumulated heat during the first month after bloom – the higher the accumulated heat, the shorter the fruit development period (Fig. 1). The fruit development period of a cultivar can vary among years by as much as 30 days and most of the effects on development occur during the early stages of fruit development. Thus, spring temperatures can have significant effects on fruit sizes and/or tree yields because, during warm springs, rates of fruit growth cannot keep up with rates of fruit development when spring temperatures are excessively high. In recent years spring temperature variability appears to be increasing. While historic mean growing degree hour (GDH) accumulations in the month after peach tree bloom in California were around 6000 GDH, recently 3 years have registered accumulations over 8000 GDH and one year was above 9000 GDH. This caused early harvests and problems with fruit size. A harvest prediction model has been developed to help growers cope with these variable weather events (http://fruitsandnuts.ucdavis.edu/Weather_Services/Harvest_Prediction__About_Growing_Degree_Hours/). In addition, prolonged temperatures > 27o C occurring during bloom have also negatively affected fruit set of prunes (Prunus domestica) and sweet cherries (Prunus avium). California prune production is especially vulnerable because it is dependent a single cultivar. Breeding efforts are under way to spread the bloom period and decrease the risk of sporadic warm spells during spring (Table 1).