120 



M. G. STALFELT 



Unfortunately, a control study of this kind often meets with great 

 technical difficulties. This apphes in particular when the plants consist of 

 large trees, as in the present investigation. 1 therefore used young (5- to 

 8-year-old) spruce plants for the control measurements, as described earlier 

 (1944). Transpiration was then measured by weighing the plants, after the 



Precipitation 

 eOOr °^ open ground 



600 



I. 



E 



400 



200 



a 

 < 



I 



L. 

 SI 



< 

 I 

 >- 



Water 

 supply to 

 the trees 



Transpiration 

 from trees on 

 ground- water 

 depth. 0'2nn 



to the 

 root zone 

 P- during Sept- 

 April 



during 

 '^ May- August 



2.7nn 



Fig. 3. Comparison between transpiration and water supply of the trees. A andB. As 

 in Fig. I. O, P, Q. Water supply to the trees from the soil below them and in the 

 gaps, as well as from the water-absorption of the needles. O. Moisture supply from 

 the ground-water and from the water-absorption of the needles. Quantity not 

 defmitely known. P. 202 mm (41% of 495 mm). Mean value for 5 spruces, and for 

 the root zone of the trees under the crowns and in the gaps. Q. 87 mm (29% of 

 298 mm); otherwise as in P. R and S. Transpiration. R. 211 mm (71% of 298 mm). 

 Mean value for 8 trees (5 in P and Q and 3 other trees on the same site), with a 

 ground-water depth of 2-7 m. S. 378 mm (127% of 298 mm). Mean value for 3 trees, 

 with a ground-water depth of about 0-2 m. 



roots had been freed from soil by suspending them in water, and wrapped 

 in aluminium foil. After several weighings, the stem was severed close to 

 the root and weighing continued for the next 5 minutes. In some cases 



