Shifts in plant phenology are a major indicator of climate change. Shifts in timing can be related to competition, including resource acquisition and access to pollinators, with species with greater phenological plasticity exhibiting greater resistance to the negative effects of climate change. For invasive species, which often exhibit higher levels of plasticity than native species, climate change may lead to increased competitive advantage within the invaded community. Therefore, phenology may be an important factor to consider in invasion biology. The vacant niche hypothesis suggests that species may be more likely to invade when there is little phenological overlap with native community members. Alternatively, the plasticity hypothesis suggests that exotic species may benefit from greater shifts in flowering phenology. Current data document advancement of spring phenology due to rising temperatures. However, studies have not investigated how native, exotic, and invasive (widespread, damaging exotic) species differ in response to warming. Using an experimental warming array at Kellogg Biological Station, Michigan, we examine differences in flowering phenology (date of first and last flower, flowering period, fruiting) between ambient and warmed (+3°C) conditions in confamilial triplets of locally native, invasive, and exotic forb and grass species representing a range of phylogenetic diversity.
Elevated temperatures, on average, advanced flowering by one week. However, this pattern was driven by invasive species, which advanced their flowering in response to warming by 30 days more than other species (invasive x warm F=7.14, p<0.05). Elevated temperatures also accelerated the days to last flower in both invasive and exotic species, while native species continued to flower later (35 days) into the season (treatment x status F=3.49, p<0.05). Similarly, elevated temperatures resulted in earlier fruit set in both invasive and exotic species, with native species setting fruit 30 days later, but this is likely due to later flowering (status F=3.48, p<0.05). Duration of flowering was not affected by either temperature or native status. Our results support the plasticity hypothesis for invasive species, and earlier-flowering invasive species may benefit from priority effects by accessing resources first. As climate change increases variability in temperature and precipitation, species with more flexible phenologies may benefit from the increased environmental variability. Given that native species’ phenology did not respond to warmer temperature conditions in our experiment, native species may not respond to climate change as effectively as invasive or exotic species, and so may be more vulnerable to extinction.