428 



REPORT OF THE COMMISSIONERS OF 







TRANSPIRATION 



KIND OF TREE 



RELATIVE 

 TRANSPIRATION 



FOR GROWING 



SEASON. 



INCHES ON 



GROUND AREA 



Ash, 



IOO. OO 



9.l8 



Birch, 

















90.2 



8.l8 



Beech, 

















89.7 



8.I3 



Hornbeam (Ironwood), 

















86.O 



7-75 



Elm, 

















80.8 



7-32 



Maple, . 

















69.I 



6.24 



Norway maple, 

















60.I 



5-45 



English oak, . 













o 





67.9 



6.15 



Oak, 













. 





48.3 



4-37 



Aspen, . 













. 





94.2 



8-54 



Alder, 

















9I.6 



8.30 



Linden, . 

















86.8 



7.87 



Larch,* . 













. 





123-3 



11. 17 



Norway spruce, 













. 





13.8 



1.25 



Scotch pine, 













. 



11.9 



1.08 



Fir (balsam), . 













. 



9.2 



0.83 



Austrian pine, . 















6.9 



0.63 



The foregoing figures give an average transpiration for the deciduous trees 

 mentioned of about 7.3 inches, while for the four conifers the average may be taken 

 at about one inch, f 



* This is probably the European larch. The American larch (tamarack) grows naturally in 

 swamps and is, like the swamp ash, a large consumer of water. Tamarack is, however, a slow grower, 

 and probably II. 17 inches per year is a large figure even for a swamp habitat. 



t In the original table from which these data are derived, the results are in kilogrammes evaporated 

 per 100 grammes of dry leaves. The data stated in this form not furnishing any basis for practical 

 computation, in order to reduce them to inches on the ground area, the percents have been computed 

 by assuming ash at 100, and the transpiration of the other species as proportionate to the number of 

 kilogrammes per 100 grammes of dry leaves, in this way obtaining the second column of the table. 

 Inches on the watershed have been computed from the data as to beech trees assuming the transpira- 

 tion, for the growing season, of the average beech tree at 8. 13 inches on the ground area, the other 

 transpiration depths being made proportionate. The results in this form are, of course, only approxi- 

 mate, but are interesting as veryfying previous data. In any case, it should be borne in mind that 

 with the infinite variations of climate and soil, such data are, and must ever remain, more or less 

 approximative. These data are also given by Mr. Nisbett in his recent work, Studies in Forestry, 

 but with figures differing somewhat from those in Bulletin No. 7. In the absence of Hohnel's original 

 paper the author has no means of determining which set is right. In any case these figures are 

 merely given for illustrative purposes, and slight variations do not therefore especially affect the final 

 results. Moreover, it may' be pointed out that " inches on the ground area " of this table are com- 

 puted on the supposition that all forests have the same density as the assumed typical beech forest. 

 As a matter of fact the density of different forests will vary greatly, the average being less than the 

 beech. On this basis the figures for inches on the ground area are undoubtedly somewhat in excess 

 of the truth. 



