The hydraulic architecture of trees and other woody plants

summary In this paper, we have reviewed how the hydraulic design of trees influences the movement of water from roots to leaves. The hydraulic architecture of trees can limit their water relations, gas exchange throughout the crown of trees, the distribution of trees over different habitats and, perhaps, even the maximum height that a particular species can achieve. Parameters of particular importance include: (1) the vulnerability of stems to drought‐induced cavitation events because cavitation reduces the hydraulic conductance of stems, (2) the leaf specific conductivity‐of stems because it determines the pressure gradients and most negative water potentials needed to sustain evaporation from leaves, (3) the water storage capacity of tissues because this might determine the ability of trees to survive long drought periods. All of these parameters are determined by the structure and function of anatomical components of trees. Some of the ecological and physiological trade‐offs of specific structures are discussed. CONTENTS Summary I. Introduction 346 II. Water flow through pipes and the unit pipe model 347 III. Parameters and concepts to describe hydraulic architecture 349 IV. Patterns of hydraulic architecture in woody plants 350 V. Vulnerability to cavitation: relation to hydraulic architecture and drought resistance 354 VI. Dynamic and steady state models of water flow in trees 355 VII. The segmentation hypothesis 357 References 359