Climate change is altering the environmental cues that drive the timing of growth and reproduction. Species vary in their ability to respond to these cues, which will influence future community composition and dynamics. In plants, phenological shifts may alter biotic interactions with pollinators, dispersers, or herbivores. Phenological plasticity in response to changing conditions has also been implicated in the success of invasive species over native species. The effects of temperature and precipitation changes may interact depending on whether rainfall variability affects the length of the winter rainy season or simply the absolute amount of rain. I investigated the individual and synergistic effects of temperature and precipitation on flowering times in plant species in the Pacific Northwest using the Wilbur L. Bluhm Phenology Dataset, which documents first flowering time from 1959 to 2016 for nearly 1900 taxa in Salem, OR, USA. I regressed first flower date against climatic data from the Salem McNary Field weather station to examine the responsiveness of flowering to variation in temperature and precipitation. I also compared the strength of these relationships between native and invasive species to address whether invasive species are more responsive to environmental cues.
Results/Conclusions
In Salem, OR, spring maximum and minimum temperatures have increased over the 57 year period. Minimum spring temperature has increased by 0.45˚C per decade (p<0.001), signaling a shift in local climate. However, spring rainfall patterns were highly variable and did not exhibit a trend. All by 7% of taxa varied in the timing of the first flowering, with the median range in flowering time being 33 days. This suggests that flowering time is plastic for a majority of taxa. Taxa also varied in their phenological response to spring precipitation and minimum temperature. Increases in spring minimum temperature and precipitation were associated with earlier flowering times, but the relationship between temperature and first flowering day was stronger.