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UNITED STATES DEPARTMENT OF AGRICULTURE 



MISCELLANEOUS PUBLICATION No. 257 



Washington, D. C. 



June 1937 



WATER UTILIZATION BY TREES, WITH SPECIAL 



REFERENCE TO THE ECONOMIC FOREST 



SPECIES OF THE NORTH 



TEMPERATE ZONE 



By Oran Raber, conservationist, Division of Forest Influences, Forest Service 



CONTENTS 



Page 



Introduction 1 



Purpose and scope 1 



General uses of water in trees 2 



Absorption of water by trees 3 



Water absorbed by shoots 3 



Water absorbed by roots 3 



. Summary and suggestions for research 7 



Storage of water in trees and water content of 



tissues 7 



Water content of wood 7 



Water content of leaves 10 



Water content related to site 14 



Summary and suggestions for research 15 



Water losses of trees .16 



Bleeding, guttation, and disposal of excess 



water 16 



Page 



Water losses of trees— Continued. 



Water lost through transpiration. 17 



Summary and suggestions for research 58 



"Adaptations" of trees to dry conditions 59 



Methods of checking transpiration 62 



Methods of assuring an adequate water 



supply 71 



Testing ability of trees to withstand 



drought 73 



Summary and suggestions for research 74 



Water consumption by trees 75 



Water requirement 79 



Summary and suggestions for research 83 



Literature cited 85 



INTRODUCTION 



PURPOSE AND SCOPE 



During the last 50 years there has been an ever-increasing stream of 

 literature dealing with the general water relations of plants. At one 

 time the emphasis was placed upon water losses and at another on 

 water absorption and the relation of the plant to the soil; in recent 

 years the emphasis has been centered on the internal cellular changes 

 associated with drought resistance. Most of this literature has dealt 

 with herbaceous types both because of the ease with which such forms 

 can be manipulated and- studied under experimental conditions and 

 because of the importance of this type of vegetation in the world's 

 food supply and its consequent dominance in agriculture. 



As the demand for water by industry, by agriculture in semiarid 

 regions, and by expanding urban populations has increased, as the 

 attention of students has been drawn by recurrent floods and excessive 

 erosion to the relation between ground cover and the water regime of 

 the soil, and as questions of the most efficient land utilization, reforest- 

 ation of submarginal lands, and the general importance of timbered 

 areas have come to be more appreciated, there has arisen a decided 



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