THROUGHFALL IN FOREST STANDS 133 



Table 4 



Standard errors of moved gauges, troughs and stem gauges, 1959. 

 (Expressed as % mean) 



Moved Stem 



Period 5-m. gauges Troughs gauges 



(5-in. gauges not moved between io-6 and 30-7.) 



random locations. The results (Table 4) show that for long or short periods, 

 the standard errors of the estimate ranged around 6%. Over a four month 

 period, there was httle to choose between moved gauges and the troughs 

 and, although with more frequent moving, 5-in. gauges would be expected 

 to give a stiU smaller standard error, the increase in labour should not be 

 minimised. 



The desired level of precision will be dependent of course, on the 

 precision of the measurements of any other phases of the water balance with 

 which throughfall is intended to be combined. Although much depends on 

 local conditions and on the application of the data, for many purposes a 

 standard error of about 5% of the mean would appear to be acceptable. 



It must be emphasised that it is the reliability or precision of the estimates 

 of total throughfall obtained by various methods which is being exairdned. 

 The mean values given in Table 5 indicate differences of up to 5% between 

 the various estimates. 



It is necessary to point out that the trough size adopted was almost 

 certainly not the most efficient for the pattern of throughfall which 

 occurred in this plantation. This pattern is related to the spacing and habit 

 of the trees, and the troughs were a little less than a quarter of the mean 

 area occupied by a tree. The size of the troughs used was still small enough 

 to reflect the relationship between catch and distance of the trough centre 

 from the surrounding trees (see Fig. 2). 



Although the results have not shown it, troughs are more susceptible 



