134 E. R. C.REYNOLDS AND L.LEYTON 



Table 5 

 Comparison of mean catch by various methods, 1959. (Inches of water) 



(*Not moved between io-6 and 30-7.) 



to bias than small gauges, simply due to the fact that they camiot be placed 

 with their centres nearer a tree than a distance of half their width. Using a 

 mathematical model approximating to the stand conditions, J. F. Scott 

 (unpubhshed) has shown that with 5-in. gauges, this bias may be in the 

 region of 2%, whereas troughs of the dimensions used could increase the 

 estimate by as much as 19% over the true mean. 



For more accurate measurements, annular gauges might well be installed 

 to sample the throughfall in the area which is not adequately sampled by 

 the troughs. There is no reason why such annular gauges should not be 

 made to incorporate stem flow measurement. 



Increasing the size of the collecting area through the use of troughs, 

 considerably increases the work of measuring and recording the large 

 volumes of water collected. An automatic measuring system has therefore 

 been devised on the principle of the tipping bucket rain gauge. The 

 movement of the bucket is made to actuate a counter directly, or electri- 

 cally through a microswitch. The trough collection can then be readily 

 measured at any interval appropriate to the investigation, with a reasonably 

 low standard error, yet without any need to move the gauges or to record 

 the collection at unnecessarily frequent intervals. 



Stem flow was measured separately on twenty random trees using a 

 plastic putty collar held in position by a copper band and receiving through- 

 fall within one centimetre of the trunk at a height of 41 ft. The percentage 



