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Key messageOur analysis of short-term growth responses to weather conditions provided evidence that the non-native tree species Ailanthus altissima may have a high growth potential in a warmer and drier environment, as predicted by global warming scenarios.AbstractNon-native tree species may alter ecosystem services in colonized forest communities. These novel forests represent a challenge for management, which is further accentuated by anthropogenic global change. Knowledge on the intra-annual growth performance and tree water relations of established and novel tree species is required to elucidate the drivers underlying forest dynamics. Here, we analysed intra-annual radial growth of the introduced tree species Ailanthus altissima (Mill.) Swingle and co-occurring Castanea sativa Mill. in novel forest communities in southern Switzerland. We used fouryears of continuously measured growth data in two sites to identify weather conditions in which the species achieved highest hourly growth and conditions in which largest proportions of seasonal growth occurred. While both species reached the largest proportion of seasonal growth and achieved the highest hourly growth under the most frequent weather conditions, A. altissima featured the highest growth rates in a wider range of weather conditions than C. sativa, particularly at hightemperature and highvapour pressure deficit. We conclude that A. altissima has a greater potential than C. sativa to sustain growth in warm-dry conditions. Importantly, the advantages of A. altissima may be more accentuated in forest stands with low interspecific competition.