COS 150-2 - Elucidating intraspecific variation in the reproductive phenology of invasive autumn olive (Elaeagnus umbellata)

Abstract: Invasive plants spread by people outside of their natural ranges can have detrimental effects on local ecosystems. Assessing the potential drivers of these biological invasions is of utmost importance. In the success of invasive plants, phenology, which is a seasonal and climate-related natural phenomenon in plants including reproduction and blooming, may have a significant role. If invasive plants have the ability to adapt to drastic changes, it may help them survive in unexpected conditions better than non-resistant species. However, knowledge of how invasive species' phenological responses to climate vary across their ranges remains limited due to the scarcity of long-term phenological information at broad spatial scales, and we lack an understanding of how phenology sensitivity to climate may facilitate invasions.

Here we posed that invasive plants show high phenological plasticity across the different climate zone to survive. Therefore, we address this impasse by leveraging historic herbarium specimens and more recent citizen science data to quantify variation in the reproductive phenology of autumn olives (Elaeagnus umbellata) and its sensitivity to climate. Elaeagnus umbellata is a highly invasive deciduous shrub that has been classified as a noxious weed by the USDA and banned in multiple states since its introduction from Asia in 1830. We find significant variation in the timing of the species’ reproduction across its invasive range in the US. Flowering time was more advanced in warmer and wetter areas, whereas fruiting time did not display clear patterns with respect to local long-term climates. However, in contrast to previous studies focused on native species in the US, we did not find significant variation in phenological sensitivity to long-term temperature and precipitation averages. This means that, unlike native species that have had time to adapt to the climate where they live, invasive species may respond to environmental changes in a similar way across their invaded ranges. In contrast, there was some variation in how the species' reproductive timing responded to temperature anomalies (the difference between annual observed temperatures and the long-term average), which suggests that phenological responses vary within the species.

Our findings highlight the importance of comprehensive, broad-range phenological assessments of invasive species, and they suggest that their apparent ability to better track temperature changes in terms of reproductive timing may be due to greater plasticity and adaptation to the conditions in their native range.