The impact of climate on flowering in the High Arctic - the case of Dryas in a hybrid zone

The extreme seasonality of the High Arctic creates very different flowering conditions for plants in areas of early and late snowmelt. Therefore, future reproductive responses to climate change may be dependent on the timing of snowmelt. We combined genetic, morphological, and long-term monitoring data on Dryas from a High Arctic hybrid zone of D. integrifolia and D. octopetala to assess whether climate variation influenced flowering differently in areas of early and late snowmelt, and whether this could have a genetic origin. We found a non-linear relationship between timing of snowmelt and flowering. The duration of the period between snowmelt and the onset of flowering (pre-floration interval) varied with the date of snowmelt. Shorter pre-floration intervals were associated with warmer average temperature during the pre-floration intervals in both early and late melting plots. However, the pre-floration interval was much shorter in early than in late plots at the same average temperature. Likewise, the interannual variation in flower abundance differed between early and late melting plots. Flower abundance was negatively influenced by frost after snowmelt in the year of flowering in early plots. In late plots, flower abundance was positively influenced by the length of the previous growing season. We identified two morpho-types in the study area, but their distribution and genetic differentiation was not related to the snowmelt gradient. We conclude that the different flowering responses found along the snowmelt gradient are a result of environmental variation. Based on our results and projected climatic change for the study area, we predict that the onset of flowering will advance and flower abundance will increase in areas of early snowmelt. In areas of late snowmelt, the onset of flowering will remain unchanged or be delayed and flower abundance will decrease.