Reproductive stages in lowbush blueberry (Vaccinium angustifolium) occur earlier with increasing temperature

Climate change is altering the timing of many plant phenological events, yet most studies focus on flowering, with less attention given to later reproductive stages such as fruit development and ripening. Vaccinium angustifolium (lowbush blueberry) is an important perennial berry species that may be sensitive to these changes. Shifts in fruit availability could affect ecological interactions (e.g., with frugivores) and economic and cultural activities, including harvest timing.

We examined digitized and physical herbarium specimens and crowd-sourced iNaturalist images of V. angustifolium. Each plant was scored into one or more of five phenological stages: bud, flower, fruit pre-veraison (green berries), fruit post-veraison (blue berries), and vegetative only. A total of 928 observations were retained, with plants spanning eight ecoregions across northeastern North America and dating from 1901 to 2023. We used multiple linear regression models to assess phenological responses to monthly temperature and shifts over time.

Warmer spring and early summer temperatures shifted the timing of all V. angustifolium reproductive stages earlier, with budding having the strongest response to temperature. In addition, we estimated a shift of approximately 7 days earlier in the timing of fruit pre-veraison over the last century.

Lowbush blueberry has a strong phenological response to early season temperatures, and the development of green berries has shifted earlier over the last century. These findings contribute to a broader understanding of how reproductive phenology of V. angustifolium may respond to climate change, with potential ecological and socioeconomic impacts.