Recurring weather extremes alter the flowering phenology of two common temperate shrubs

Background/Question/Methods

The aim of this study is to explore the effects of heavy rain and drought, on the flowering phenology of two shrub species Genista tinctoria and Calluna vulgaris. We conducted a field experiment over five consecutive years in Central Europe, applying annually recurring extreme drought and heavy rain events on constructed shrubland communities and recorded the flowering status. Further, we observed spring temperature as well as precipitation and correlated these data with the onset of flowering.

Results/Conclusions

Both species showed a response to extreme weather events: drought delayed the mid flowering date of Genista tinctoria in three of five years by about one month and in one year advanced the mid flowering date by 10 days, but did not affect the length of flowering. Mid flowering date of Calluna vulgaris was not affected by drought, but the length of flowering was extended in two years by six and ten days. Heavy rainfall advanced mid flowering date and reduced the length of flowering of Genista tinctoria both by about two months in a particular year. Mid flowering date of Calluna vulgaris was not affected by heavy rain, but the length of flowering was reduced in one year by 4 days. Our data suggest that extreme weather events, including alterations to the precipitation regime, induce phenological shifts of plant species by a substantial magnitude. Thus, the impacts of climate extremes on plant life cycles may be as influential as gradual warming. Particularly, the variability in the timing of precipitation events appears to have a greater influence on flowering dynamics than the magnitude of the precipitation.