Linking wood density with tree growth and environment: a theoretical analysis based on the motion of water

Summary • An hydraulic model of a tree stem is presented to help understand how the carbon storage in ecosystems varies with changing environmental conditions. • The model is based on the assumption that a tree stem is a collection of parallel pipes and was used to (qualitatively) predict how the mass concentration of dry matter ( D ) would vary with water temperature (via changes in viscosity), nitrogen supply and atmospheric CO 2 . • There was qualitative agreement between model predictions and observed gross trends. The model predicted that the flow rate would be relatively insensitive to variations in D in angiosperm stems; this was consistent with observations. It is concluded that other factors need to be considered to explain variations in D in angiosperm wood. The flow rate of water through gynmosperm stems was predicted to be very sensitive to variations in D and the model explained why D ; decreases with decreases in water temperature, decreases with increases in nitrogen supply and increases with elevated CO 2 . • The model captured some of the important underlying relations linking water transport with wood density and environment and qualitative testing of the model is recommended.