First flowering of wind-pollinated species with the greatest phenological advances in Europe

Increasing risk of pollinosis (hay fever) is one of the most anticipated consequences of climate change on human health. Wind-pollinated plants are representative of allergenic species because they include species with the highest capability of causing allergy-related diseases in humans. Therefore, changes in wind-pollinated species may reflect impacts of climate change on allergenic plants. In particular, flowering is one of the developmental stages most affected by climate change. This report specifically addresses changes in flowering dates that have occurred during the three decades 19712000 as a function of pollination mode and woodiness. The assessment is made using a phenological data set comprising trends of flowering dates of 29 species in 983 locations in Europe. Linear mixed models assessing the statistical significance of trends while adjusting for spatial correlation are used. The main results indicate for the first time that the onset of flowering of wind-pollinated plants advanced more than for insect-pollinated plants, while full flowering phases tended to advance less. These novel findings are contrary to the results of Fitter and Fitter (2002) for Oxfordshire, who reported larger advances of insect-pollinated plants. Onset of flowering and full flowering of insect-pollinated species are more likely to advance for seasons early in the year; instead, wind-pollinated plants showed no dependence of trends on the season (first flowering) or a decreased advance of phases that are early in the year (full flowering). The effect of woodiness could not be unambiguously defined, but seems to be of minor importance. The presented findings suggest a lengthening of the flowering period in general, which might lead to an increasing time of exposure to airborne pollen of allergic subjects, with consequent likely increment in severity and incidence of allergic symptoms.