Consistent flowering response to global warming by European plants introduced into North America


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1. The reliability of species distribution models (SDM) to predict the probable response of alien plants to climate change rests on the assumption that plant performance in relation to temperature in the introduced range will be similar to that observed in the native range. Yet, alien plants may exhibit enhanced performance or different environment-distribution relationships following their introduction into a new area. Empirical data are therefore essential to test whether the responsiveness of species to climate is equivalent in the native and introduced ranges.

2. This study tests the assumption that phenological responses of plants to temperature are similar in both their native and introduced range. First flowering date (FFD) is widely used to assess the responsiveness of plants to recent warming arising from global change. For 19 species native to Europe, FFD observed in both the UK and USA between 1970 and 2000 was examined in relation to interannual variation in local temperatures. General trends, variability and responsiveness of FFD to warming were examined for consistency in the contrasting climate of Oxfordshire and Washington DC.

3. Mean FFD in Oxfordshire was a powerful predictor of the same variable in Washington DC, although summer flowering plants in Oxfordshire tended to flower earlier in the season in Washington DC. FFD varied considerably over 30 years, but across all species, the range in FFD revealed a similar trend in both regions with larger ranges observed for earlier flowering species.

4. Comparable trends were found between Oxfordshire and Washington DC in the degree to which flowering advanced or regressed per unit temperature increase. In response to warming, the majority of species flowered earlier in both countries and the degree to which FFD responded to increasing temperature was greatest for species flowering earlier in the year.

5. These equivalent phenological responses to temperature across continents imply prediction of the performance of alien plants under climate change may be derived from a species’ behaviour in its native range. While these findings support the use of SDM, they also indicate that these models could be significantly improved through the integration of phenological relationships parameterized from data in the native range.