Growing‐Season Precipitation Is a Key Driver of Plant Leaf Area to Sapwood Area Ratio at the Global Scale

ABSTRACT Leaf area to sapwood area ratio ( A L / A S ) influences carbon sequestration, community composition, and ecosystem functioning in terrestrial vegetation and is closely related to leaf economics and hydraulics. However, critical predictors of A L / A S are not well understood. We compiled an A L / A S data set with 1612 species‐site combinations (1137 species from 285 sites worldwide) from our field experiments and published literature. We found the global mean A L / A S to be 0.63 m 2 cm −2 , with its variation largely driven by growing‐season precipitation ( P gs ), which accounted for 18% of the variation in A L / A S . Species in tropical rainforests exhibited the highest A L / A S (0.82 m 2 cm −2 ), whereas desert species showed the lowest A L / A S (0.16 m 2 cm −2 ). Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on A L / A S , whereas soil pH was negatively correlated with A L / A S . Tree density accounted for 7% of the variation in A L / A S . All biotic and abiotic predictors collectively explained up to 45% of the variation in A L / A S . Additionally, A L / A S was positively correlated to the net primary productivity (NPP) of the ecosystem. Our study provides insights into the driving factors of A L / A S at the global scale and highlights the importance of A L / A S in ecosystem productivity. Given that P gs is the most critical driver of A L / A S , alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches.