The number o£ basic sample units used in the 

 survey corresponded to the number of logging opera- 

 tions on which measurements were taken. Before start- 

 ing fieldwork in a State, an estimate was made of the 

 number of sample units needed to assure a standard 

 error of total residue volume of not more than ±20 

 percent to meet Forest Survey objectives. For the 

 survey reported here, 39 sample units--23 in Arizona 

 and 16 in New Mexico- -were drawn from a list of known 

 active logging operations in the two States. These 

 were drawn at random from strata defined by land 

 ownership and operator size class. Two ownership 

 classes were used--National Forest and other owners. 

 Operator size class corresponded to the production 

 class of the sawmill for which the logging was being 

 done. Two size classes were used--small (less than 

 10 MMBF per year) and large (10 MMBF or more per year) . 



Enough trees were measured on each sample unit 

 to provide a product volume of between 4 to 10 MBF 

 per sample unit. On the basis of previous survey 

 experience, guides were developed so that field crews 

 could estimate the number of trees to be measured to 

 meet volume objectives. The number of trees varied 

 with the range in average tree size, timber type, and 

 stand age (young or old growth). From 10 to 30 trees 

 were recommended for each sample. Actually, 574 prod- 

 uct trees were used, an average of 15 per sample unit. 

 The net product volume scaled was 52,107 cubic feet 

 (equivalent to 328,269 board feet), an average of 8.4 

 MBF per sample unit. 



Trees felled for products were measured in place 

 to determine both product and residue volumes. Resi- 

 due volume from other trees destroyed or cut when 

 product trees were felled also was measured. Skid- 

 ding damage to trees along skid trails was determined 

 after logs reached a landing, except in those cases 

 where crews had been on hand to witness damage as it 

 occurred. 



In clear-cut operations where there was difficulty 

 in relating felling and skidding damage to individual 



8 



