Increase in CO2 concentration could alter the response of Hedera helix to climate change.

Increasing CO 2 concentration ([CO 2]) is likely to affect future species distributions, in interaction with other climate change drivers. However, current modeling approaches still seldom consider interactions between climatic factors and the importance of these interactions therefore remains mostly unexplored. Here, we combined dendrochronological and modeling approaches to study the interactive effects of increasing [CO 2] and temperature on the distribution of one of the main European liana species, Hedera helix. We combined a classical continent-wide species distribution modeling approach with a case study using H. helix and Quercus cerris tree rings, where we explored the long-term influence of a variety of climate drivers, including increasing [CO 2], and their interactions, on secondary growth. Finally, we explored how our findings could influence the model predictions. Climate-only model predictions showed a small decrease in habitat suitability for H. helix in Europe; however, this was accompanied by a strong shift in the distribution toward the north and east. Our growth ring data suggested that H. helix can benefit from high [CO 2] under warm conditions, more than its tree hosts, which showed a weaker response to [CO 2] coupled with higher cavitation risk under high temperature. Increasing [CO 2] might therefore offset the negative effects of high temperatures on H. helix, and we illustrate how this might translate into maintenance of H. helix in warmer areas. Our results highlight the need to consider carbon fertilization and interactions between climate variables in ecological modeling. Combining dendrochronological analyses with spatial distribution modeling may provide opportunities to refine predictions of how climate change will affect species distributions.