Abstract/Summary

The phenology, or timing of key life-history events, of many globally important crops and the insects that pollinate them are shifting because of the changing climate. Where these temporal shifts occur at different rates or in different directions, it induces a risk of phenological mismatch, potentially reducing the quality and quantity of crop production. This study makes use of 48 years of UK citizen science (pollinating bee records) and systematic (apple flowering) data to report phenological shifts of apples and their bee-pollinator community. It quantifies the mismatches between peak flowering and flight dates which could potentially cause pollination deficits. Flowering onset and peak flowering dates of Bramley apples advanced throughout the study period. This advance was primarily driven by early spring temperatures, with peak flowering dates advancing by 6.7 ± 0.9 per 1 °C warming. In addition, increasing spring rainfall significantly delayed flowering dates by 0.4 ± 0.1 days per 10 mm additional rainfall. By contrast, bee phenology shifted in a non-linear manner, advancing from 1970 to 1985 before plateauing until the end of the study period. The peak flight date of the apple pollinating bee community appears to be similarly sensitive to spring temperatures, experiencing an advance of 6.5 ± 2.1 days per 1 °C warming, although individual bee species responses to climate varied. Furthermore, this study compared the phenological trends to assess the potential risk of asynchrony between crop and pollinator phenology. The different response patterns in the phenology of apples and bees led to shifting patterns of temporal mismatch between peak flowering and peak flight over time. Differences in sensitivity to climate do not appear to directly contribute to the phenological mismatch. Finally, this study highlights the potential value of citizen science data (with sufficient quality control) in understanding phenological shifts and mismatches and highlights potentially increasing temporal mismatch between apple trees and their bee pollinators.