An evolutionary attractor model for sapwood cross section in relation to leaf area

► Sapwood cross-section per unit leaf area (SA:LA) influences hydraulics and stem costs. ► A revenue-minus-cost model mostly predicts higher SA:LA under water stress. ► Large soil-to-root resistance caps benefits obtainable from increasing SA:LA. ► Maximizing height rather than revenue-minus-cost predicts different outcomes. ► Evolutionary-attractor theory for SA:LA complements existing hydraulic models.