Climate Zones Shape the Global Diversity of Sexual Systems in Forests Woody Plants

Sexual systems critically influence woody plant evolution and forest functioning, yet their global patterns and environmental drivers remain understudied. Investigating the environmental correlates of sexual systems in woody plants is essential for developing targeted conservation and restoration strategies for forest ecosystems. We analyzed sexual system composition of 3595 woody species from 30 ForestGEO forest plots spanning tropical, subtropical, and temperate zones in the Northern Hemisphere. Species were classified by sexual system (hermaphroditism, monoecy, and dioecy) and growth form (trees and shrubs). Community-level patterns were assessed across climatic zones, and the relative contributions of climatic, spatial, and topographic factors were quantified using multivariate and network-based analyses. We observed the following: (1) Sexual system composition exhibited clear climatic differentiation: dioecious species predominate in tropical forests, while monoecious species increased in dominance toward temperate regions. (2) Climatic variables, particularly temperature and precipitation, accounted for more variation in sexual system composition than spatial or topographic factors, although their relative influence differed among climatic zones. (3) Distinct life-form-specific patterns were detected: sexual systems of trees were more strongly associated with broad-scale climatic gradients, whereas those of shrubs were more closely linked to spatial structure and local environmental heterogeneity. Together, these results demonstrate that climate is a dominant but life-form-dependent driver of sexual system biogeography in woody plants, improving trait-based understanding of forest biodiversity responses to climate change.