Trees, including globally threatened species, are introduced outside their native ranges, where they can pose conservation risks or benefits. A key question is understanding the global extent and drivers of non-native tree introductions. Using over 31 million occurrence records of 50,470 tree species, we find that 26,096 (51.7%) were introduced as non-natives, and 167 (63.7% of the global total) families harbor threatened non-native species. The introductions of all species and threatened ones are phylogenetically conserved. South America, North America, and temperate Asia had the highest richness of non-natives, while Europe had the highest percentage (88.4%) of non-natives, with intracontinental flows dominating introductions. Taller species, those with lower leaf phosphorus and higher specific leaf area, are more frequently introduced, with increasing non-native richness associated with warmer, wetter climates and higher social development, a pattern that differs from that found for native species. The prevalence of early successional and competitive traits underscores the potential risk of future invasion, urging policies that prioritize native biodiversity.
Zhu et al. (2026) studied this question.