Invasive plants have a delayed and longer flowering phenology than native plants in an ecoregional flora.

Abstract

Background and aims: Flowering phenology has been suggested as an important factor to explain invasions of non-native plant species. Invasive species success may be enhanced by flowering at different times (the vacant niche hypothesis) or flowering for longer periods (the niche breath hypothesis) than native species. However, comprehensive regional assessments of the flowering phenology of invasive and native floras are lacking in the literature. In this study, we evaluated the flowering phenology of invasive and native plant species pools to test the above-mentioned hypotheses within a biogeographically meaningful region.

Methods: We investigated the start, end, and length of flowering between the invasive and native floras that occur at the same elevation range in the Cantabrian Mixed Forests ecoregion (NW Iberian Peninsula), a biogeographical hotspot for invasive plants in SW Europe. We also accounted for species habitat preferences and climatic and biogeographic origin of the invasive species.

Key results: We found a mismatch in flowering time between the ecoregional invasive and native floras. Invasive species had a delayed and longer flowering phenology compared to native species. These differences in flowering time were more pronounced in man-made habitats and in invaders from temperate and tropical regions.

Conclusions: Our results are consistent with the vacant niche hypothesis; the asynchrony in flowering time could allow invaders to exploit a temporally empty niche. Our results are also consistent with the niche breath hypothesis, suggesting that invasive species exhibit a longer flowering period than natives, which may allow them to have prolonged access to resources. Future studies should explore the phenological patterns of invasive and native species across biogeographically relevant regions to enhance our understanding of large-scale invasion events.