ESTIMATES COVERING PART OF TOTAL AREA 273 



which differ in average height and diameter must be estimated sepa- 

 rately. 



5. Count all the trees on the area and tally a fixed percentage such 

 as 1 in either 3, 4 or 5, whose volumes are found as by method 4 above. 



6. Count all the trees on the area and determine their volume by 

 arriving at the contents of an average tree. This may be done: 



By guessing at the average contents. 



By selecting a tree of average diameter and height and determin- 

 ing its contents by the use of volume table. 



By determining the number of logs per tree or average mer- 

 chantable height expressed in logs, thus getting the total 

 number of logs on the area and then guessing at the con- 

 tents of the average log or number of logs per thousand. 



Method 6 may be applied to all of the timber considered as one 

 class, or the timber may be separated into two or possibly three dif- 

 ferent classes, corresponding with marked differences in size and char- 

 acter. 



219. Estimates Covering a Part of the Total Area. The Strip 

 Method. There are two methods generally employed to estimate a 

 portion of the area, the strip method and the plot method. The strip 

 method adopts the principle of endeavoring to obtain the average 

 stand per acre for the whole area, from the portion estimated by the 

 running of strips parallel or in a given direction and spaced at mechanic- 

 ally regular intervals. By this means it is sought to eliminate judg- 

 ment or choice in the obtaining of the required average. 



This average is still further improved by the choice of direction of 

 running these strips. The effect of differences in elevation and in drain- 

 age or soil moisture is to produce differences in the density and character 

 of the forest corresponding with these changes. The belts of forest 

 which have comparatively uniform stands usually run parallel with 

 contour lines and at right angles to the direction of slope. A basic 

 principle of strip estimating is therefore to cross these belts at right 

 angles or proceed directly up and down slopes or directly across the 

 larger stream or drainage bottoms as far as possible, and to avoid 

 traveling along contour lines or bottoms and in general along the long 

 axis of belts of timber. ■ If this fundamental principle is neglected, 

 very large errors may be incurred in applying the average estimate 

 so obtained to the larger area. 



In rectangular surveys, it is customary to run the strips in one of 

 two cardinal directions, and the choice is therefore narrowed down to 

 either north and south, or east and west. In irregular surveys, or 

 where the topography is so mountainous that the estimate will be made 



