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



transpiration in a windy place was about twice what it was where 

 there was no wind. Seybold (189, p. 98) in his rather extensive 

 researches, found that in Taxus baccata and Quercus ilex the ratio 

 of transpiration in a calm to that in a wind was 1:1.1 to 1.2. The 

 effect of wind on transpiration seemed to be greater in leaves with 

 cuticular transpiration than in leaves whose transpiration is primarily 

 stomatal. In the latter case the transpiration from the cells is into 

 the intercellular air spaces, while in the former the water loss is directly 

 into the surrounding air; it is, therefore, natural to expect the effects 

 produced by wind to appear more quickly in cuticular than in stomatal 

 transpiration. This may explain the results of Fritzsche (61), who 

 found that wind affects the transpiration of hardwoods more than that 

 of conifers like spruce and fir, although Douglas fir occupies an inter- 

 mediate position. In some species wind even tends to cause a closing 

 of the stomata and a resultant decrease in transpiration ; so that while 

 wind may decrease the relative humidity, it does not necessarily 

 increase the transpiration. Rubner points out also that relative 

 humidity in forests is higher than in the open because of the decreased 

 ail' movement; the trees tend to check exchanges between the interior 

 of the woods and the air outside, although, to be sure, some diffusion 

 always occurs. 



Gail and Long (64) noted, in Idaho, that Pinus contorta was much 

 more limited in its distribution than P. ponderosa, the former being 

 restricted to the areas protected from the wind. When the effect of 

 air movement on the transpiration rate was studied, it was found that 

 the transpiration in P. contorta was increased by the wind more than 

 four times as much as that of P. ponderosa, as seen in table 17. This is 

 an interesting example of distribution influenced by transpiration rate 

 as affected by wind. 



Table 17. — Effect of air movement on transpiration rate in two species of pine 



Species and air condition 



Leaf area 

 per gram, 

 dry weight 



Water lost 

 per gram, 

 dry weight 



Water lost 



per gram, 



fresh weight 



Water lost 

 per square 

 decimeter 

 of leaf area 



Increase in 

 water loss 



in wind 



over that in 



still air on 



basis of leaf 



area 



Pinus ponderosa: 



In still air 



Square deci- 

 meters 



0. 9270 



.7692 



1. 47S0 

 1.0910 



Grams 

 11.53 

 13.86 



9.26 

 11.87 



Grams 

 3.56 

 5.25 



2.35 

 4.36 



Grams 

 12.31 



14.63 



6.71 

 11.74 



Percent 



} 18. 85 



} 74. 98 



In wind 



P. contorta: 



In still air 







Wind velocity in forests. — Schubert (185) (table 18) reported the 

 wind velocities in an opening in a beech thicket 4 m high as compared 

 with those in the surrounding open country. 



Table 18. — Wind velocities in an opening in a beech thicket and in open country 





Height above ground (meters) 



Velocity per second 



Ratio 





In open 



In thicket 



0.2 



Meters 

 1.76 

 2.94 

 3.85 



Meters 

 0.42 



.37 

 .83 



Percent 

 24 



2.2 



13 



4.2 



22 







