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Invasive plants grow taller under experimental warming, but mediated effects of biotic interactions are species-specific

Ivison, Katy1; Vange, Vibekke2; Speed, James2; Dawson, Wayne3

Published Oct 22, 2024 on Dryad. https://doi.org/10.5061/dryad.866t1g20w

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Abstract

Understanding the responses of non-native plants to climate change while accounting for biotic interactions is key to predicting and mitigating future invasion risks. Non-native invasive plants may benefit from or decline in the face of climate change, relative to native competitors. Non-native plants might also suffer less than native plants from natural enemies such as herbivores, which could give non-natives a competitive advantage. However, we lack an understanding of how non-native plants will compete with native plants in a warming climate, while accounting for the effects of herbivore pressure. To test the potential interactions between warming, herbivore pressure and competition, we set up a common-garden experiment in Trondheim, Norway, using five non-native plants growing either alone or in competition with a native plant community. These plants were subjected to herbivore exclusion and artificial warming treatments, using open-top chambers. We found that under warming, three non-native species had greater biomass and all five species were taller than when grown without warming. Competition with native species reduced the biomass of three non-native species and herbivore exclusion resulted in taller plants for three non-native species. Furthermore, the native community was not affected by competition with any non-native plant except Centaurea montana, which resulted in lower native community biomass, suggesting that C. montana is likely to be the most detrimental of these non-native species to native communities. Competition with natives reduced the positive effects of warming on biomass for only one species, Alchemilla mollis. Our study strongly suggests that a warming climate may benefit invasive plants more than native plants, but for some species these effects will be mediated by biotic interactions in idiosyncratic ways, depending on the identity of both native and non-native species. This will present a challenge to predicting plant invasion success under climate change while accounting for biotic interactions.