Water Uptake, Storage and Transpiration by Conifers: A Physiological Model

Abstract

As part of an ecosystem study, addressed are the questions of water utilizationby coniferous forests and the influence water has on growth and mineral cycling.Individual trees are an integrated system by themselves. Their water flux canbe envisioned as representing an integration of four components: (1) uptake,(2) internal storage, (3) the controls upon the rate of movement of water fromone part of the system to another and (4) the atmospheric demand. The objective of this chapter is to present a conceptual framework for themovement of water through individual trees from the soil to the atmosphere.Conifers are of special interest because they illustrate the importance of internalstorage and exhibit year-around physiological controls upon water movement. The demand for water, as Gates has presented in Part 3:A of this volumeis a function of the atmospheric environment and leaf geometry. The movementof water in the soil to the roots and its uptake from different zones has beentreated in Part 2 of this volume. The same general principles are assumedto operate on conifers but the relationships are simplified to apply them tothe variable environment associated with tall trees with widely distributed roots. In a previous paper a computer simulation model was constructed to accountfor daily uptake, storage, and transpiration by conifers (Running et al., 1975).The same basic design applies here but to account for significant changes indiurnal behavior the model's structure has been refined and the resolution changedto hourly. The exact equations for this hourly model await derivation anddepend upon experiments requiring simultaneous measurements of importantvariables.