80 MISC. PUBLICATION 257, U. S. DEPT. OF AGRICULTURE 



is found, to 30 inches, where Picea occurs, and the temperature falls 

 from 75° to 60° F. (mean maximum during the growing season). 



Sperry {201) studied the diameter growth and transpiration of 

 various conifers in different sites, but worked chiefly with Finns 

 contorta, P. ponderosa, and Pseudotsuga taxifolia. The lodgepole 

 pine transpired most and also showed the greatest diameter growth, 

 followed by ponderosa pine and Douglas fir. All transpired most in 

 the site of the lodgepole pine and least in that of the Douglas fir. 

 Sperry therefore concludes that this is also the order of their water 

 requirement. Although the water requirement in its technical 

 sense was not determined, between June 16 and August 25 lodgepole 

 pine transpired 0.120 cc per gram of green leaf per hour; ponderosa 

 pine, 0.091 cc; and Douglas fir, 0.066 cc. The order is thus seen to 

 be the same as that determined by Bates. Furthermore, as might be 

 expected, ponderosa pine fluctuated less in the other two sites than 

 did the other two species when transferred to the other sites. 



When one tries to transfer the water requirement for a given species, 

 as based on pot or individual experiments, to mature stands, numerous 

 difficulties are encountered, as mentioned above, but Von Hohnel 

 attempted to calculate the annual consumption of water of a hectare of 

 a closed stand in terms of inches of rainfall over the crop area. He 

 arrived at the figures of 233 mm for a beech stand 50 to 60 years old 

 and 272 mm for a stand 115 years old. 



According to Vater {219) the annual increment of beech and spruce 

 on site class II and of pine on site class I are about equal (7,000 kg), 

 as based on the somewhat unreliable data of Ebermayer. He thus 

 computed an annual consumption of water per hectare of 290 mm for 

 beech, 255 mm for spruce, and 103 mm for pine. 



Burger {24) shows that while spruce seems to transpire one-fifth as 

 much as beech, when one calculates the weight and size of the needles, 

 number of trees in the stand, etc., the loss from a given timbered area 

 is about the same. Based upon the fact that beech produces per hec- 

 tare 5,000 kg of dry substance and spruce 5,700 kg, the spruce may 

 actually use more water per year than the beech; and Burger came to 

 the conclusion that the water needs, expressed in terms of millimeters 

 of precipitation, are approximately the same for these two species. 

 More precisely, his figures are 210 mm of water for beech, 170 to 180 

 for spruce, 120 for oak, and 47 for pine. 



Copeland {38), who computed the transpiration for the chaparral of 

 California, came to the conclusion that while Ceanothus transpires 

 annually enough water to cover an area equal to that of its entire leaf 

 surface to a depth of 2 feet, Quercus vaccinijolia Kellogg and Castanop- 

 sis transpire only half that amount. He suggested that it might be 

 advantageous to replace one group of species with the other if possible. 



Various other workers have tried to compute the amount of precipi- 

 tation water for various stands and areas. Among these might be 

 mentioned the work of Anders {4) on elm, Vogel {221) on oak and 

 spruce, Von Hohnel {98, 99) on beech, and Hartig {91) on the common 

 economic species of Germany. Attention has already been called, 

 however, to the difficulties and errors involved in such calculations. 



Also, as has been mentioned above, many difficulties are en- 

 countered in transferring values from pot experiments to the field, par- 

 ticularly in the calculation of transpiration. What is the area of the 

 leaf surface of a stand? Illick and Aughanbaugh {113) calculated that 



