Leaf-level physiological measurements can reveal the process of changes in CO2 and H2O exchange rates according to environmental changes. Treelevel physiological measurements have an intermediate role in scaling-up from leaf-level
measurements to canopy-level CO2 and H2O exchange. Sap flow measurements, which
clarify tree-level water use, are useful for examining the relationship between leaf-level
H2O exchange and stand-level H2O exchange.