Latitudinal gradient patterns and driving factors of woody plant sexual systems in forest communities in the Northern Hemisphere.

Introduction: Sexual systems are key functional traits influencing the ecology and evolution of woody plant communities, yet their variation across climatic gradients remains insufficiently understood. Methods: We compiled data on 3,595 woody species from 30 forest dynamics plots spanning tropical, subtropical, and temperate zones across the Northern Hemisphere. Large-scale patterns were analyzed using linear regression, redundancy analysis, and structural equation modeling. Results: The proportion of monoecious species increased with latitude, whereas dioecious species decreased, revealing contrasting latitudinal trends. Climatic factors, particularly temperature- and precipitation-related variables, were the primary drivers of these patterns, with stronger climate-sexual system relationships observed in trees than in shrubs. Discussion: These results demonstrate that geographic variation in woody plant sexual systems is closely associated with climatic gradients. The consistent variation in monoecious and dioecious species across environmental gradients highlights the ecological relevance of sexual systems and suggests that they may provide useful trait-based information for understanding forest community responses to environmental change. Further long-term studies are needed to evaluate their potential monitoring value under ongoing climate change.