Global patterns and drivers of tree introductions

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.