Hazel trees bloom earlier than ever, raising hay fever concerns

This year, hazel trees are flowering earlier than ever, potentially causing hay fever, according to Nature Today. “We’ve never seen such early and widespread hazel blooms. Likewise, the Leiden University Medical Center (LUMC) has never recorded this much hazel pollen in December before.” Pollen levels in the air are monitored by the LUMC and Elkerliek Hospital in Helmond.

Nature Today attributes the early hazel blooms to the unusually high December temperatures. “The beginning of hazel flowering is around 40 days earlier than it has been since 1977.”

Prior to 2004, the LUMC’s rooftop pollen trap never detected hazel pollen in December. “The previous record for the highest daily concentration was six pollen grains, observed in 2022,” Nature Today says. “This year, on December 18, hazel pollen reached 12 grains per cubic meter of air.”

Alder trees have also started flowering, potentially causing hay fever. Nature Today notes that it is still uncertain how the upcoming frost will impact these tree species.

On average, hazel trees now begin blooming around 40 days earlier than they did before 1977. This year marks the earliest recorded bloom and could be a sign of the warming climate in the Netherlands and across Europe.