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



Table 3 

 Standard errors of Stationary 5-in. gauges, 1959. (Expressed as % mean) 



Simple Regression 



Period S.E. method Stratification 



In the present investigation, there was some improvement in precision 

 compared with that of the simple mean (Table 3). 



As another approach (cf. Kittredge et ah, 1941), the data were stratified 

 into three zones corresponding to <50, 50-80 and >8o% of the crown 

 radius ; the use of relative positions of the gauges under the crown allows 

 for variations in crown size. The areas of these zones were readily calcu- 

 lated from a number of random locations. For each zone, the mean catch 

 and its variance were calculated, and a value obtained for the stand as a 

 whole by weighting the means according to the areas represented. The 

 standard errors obtained (Table 3) were again about o-y times those asso- 

 ciated with the simple mean of all the gauges, and so still rather large. 



Besides these mathematical methods, the effect of moving another set 

 of twenty 5-in. gauges to new random positions after approximately each 

 inch of incident precipitation was tested. As is evident from Table 4, over a 

 period of four months involving five different gauge distribution patterns, 

 the standard error of 5-7% indicated a definite improvement over the 

 stationary gauges, although the variabiHty within any individual distribu- 

 tion pattern was similarly high. 



A more logical solution to the problem of measuring precipitation under 

 trees would be to increase the gauge size so as to integrate the throughfall 

 pattern over a larger area. 



In Germany, Delfs (1955) reports the use of troughs 20 cm wide and 5 m 

 long, but, in the absence of replicated measurements, no information is 

 available as to the precision of the estimates, and it is impossible to decide 

 therefore, whether or by how much troughs are superior to small gauges. 



Troughs have also been tested in the present investigation; these had 

 rectangular collecting areas, 3 ft x 2 ft, i.e. forty-four times that of the 5-in. 

 gauges. Twenty troughs were placed in the area with their centres at 



