field time to 812 man-hours. But if cubic-volume strata are used at the same cost of 27 man- 

 hours, the needed field plots could be reduced to 35 and the required man-hours on the ground 

 to 490. Unfortunately this example is based entirely on the gain in volume estimating. The 

 basic data are inadequate for such an analysis of gain in estimating management needs. Never- 

 theless, the rank given the various photo methods is at least an indication that the use 

 of photo-volume strata may result in cost savings for these surveys also. 



APPLICATION 



The use of aerial photos in volume and management inventories involves some form of 

 double sampling. Development of a complete sampling plan for a specific project using both 

 aerial photo and ground sampling requires consideration of both accuracy and cost. The 

 statistical methods used have been well developed in several publications (1, 3). 



In this study aerial photo -stratification schemes have been compared and rated by the 

 simplest and most practical methods available. These data indicate that photo-volume classes 

 are best in volume estimating and probably best in management inventory. 



In spite of numerous studies made during the last decade in aerial photo estimating and 

 the use of photo -volume strata, several reasons are repeatedly given for not capitalizing on 

 this technique. These include: 



1 . Cubic-volume strata may be of Little value in estimating board-foot volume or 

 management needs . 



2. Skilled photo interpreters and necessary aerial volume tables are not available 

 when needed, and therefore photo-volume strata are unusable. 



3 . The number of measured field plots has reached an irreducible minimum in 

 management plan inventories, and therefore additional photo effort will not pay off. 



All these make good excuses but poor reasons . The analysis of these data indicates that 

 cubic-volume strata are even more valuable in estimating board-foot volume than in estimating 

 cubic-foot volume. And of all strata tested, cubic-volume strata rank highest in segregating 

 both high risk sawtimber volume and young stands where management prescription is required. 

 No such analyses exist to prove the superiority of the stratification schemes now in use. 



InabiLLty to hire photo interpreters skilled in forest measurement techniques is no justifi- 

 cation for ignoring the possibilities of these techniques . When unskilled foresters are hired for 

 field plot measurement, they are not only given on-the-job training but are expected to precisely 

 measure almost all items reported in the belief that their measurements will be better than 

 their estimates . Equally unskilled foresters assigned to photo interpretation receive Little on- 

 the-job training and are asked to estimate everything without measurement. Yet, the same 

 laws of accuracy apply equally to field and photo measurements and skilled personnel must be 

 developed in the same manner . 



Aerial volume tables are not quite as common as ground volume tables , but generalized 

 aerial tables are available. When used for volume stratification as described in this paper, 

 composite tables published in 1956 and compiled from field plots .measured in southern Idaho, 

 Wyoming, and Utah, gave satisfactory results in this study in northwest Montana. 



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