45 



crop. But this involves the expenditure of so much time 

 and labour that, except where a very accurate plan is 

 required and is justified by the high revenue expected from 

 the forest, it is generally best not to employ it. It may, 

 however, suitably be used when, as frequently happens, only 

 one or two species irregularly distributed in a mixed crop 

 are saleable, and when the plan is to provide for the work- 

 ing of those species only. In such cases the cost is not unduly 

 high and the results obtained from countings over sampre 

 areas are unsatisfactory. 



The chief considerations which should determine the 

 method to be adopted may be summed up as follows : — ■ 



The purpose of the survey and the degree of accuracy de- 

 manded in the plan. — It may be only necessary to ascertain 

 the average production per acre, so as to calculate the yield 

 in the manner described in the selection method. It is 

 usually unprofitable to attempt to calculate the material 

 on the ground with extreme accuracy ; and, in any case, even 

 complete enumeration and cubing of each individual tree 

 might not ensure accuracy. 



The nature of the crop.— Enumeration by sample plots 

 should be avoided in the case of very irregular and open 

 crops, or in crops containing only scattered trees for enu- 

 meration as in the case of selection-worked areas in which 

 only one or two species sparsely distributed in a mixed crop 

 are exploitable. Again the method is unsuited to the case 

 of very small areas ; as there would be difficulty in selecting 

 plots representative of the whole. 



Method of sample plots : selection of the plots. — Where the 

 conditions are such that the method of survey by sample 

 plots is justifiable separate plots should be marked off in 

 each distinct type of growth. They should he chosen so as 

 to represent fairly the average conditions of the crop or parti- 

 cular type of growth of which a pattern is taken. 



Linear Survey.— In some cases it may be more conveni- 

 ent to use sample lines taken at regular intervals through 

 the forest. Where the crops are mixed and variable, the 

 position of the lines should be traced on the map on which 

 the limits of the different types of forest are shown, and 

 the results should be calculated separately for each crop 

 through which the lines run. The width of the lines should 

 be fixed so as to be convenient for purposes of calculation. 



Thus a line 1 chain broad would represent 0-1 acre per chain-length ; and. if the 

 type of forest ihrough which the line led was found to measure, say, 6 acres, while 



