40 Forest Mensuration 



Advantages of the gridironing method are: 



0. A topographical map is obtained at a slight extra expense. The 

 original survey is controlled and the area of the tract is re-ascertained. 



b. Cruisers are forced to traverse all sorts of country and are not 

 allowed to skip swamps, cliffs, etc. 



c. The proportion of fiats, ridges, slopes, swamps, farms, or farm 

 soil, pastures, etc., is found at the same time. 



d. The strips may be used as permanent statistical sample plots, if 

 they start from definite points (corners) and run in definite directions. 



e. The procession of the cruisers is uninterrupted by stops; hence no 

 loss of time. 



For a picture of a convenient tally sheet holder see Graves' Handbook, 

 page 123. 



The gridironing method has been adopted by the working plan division 

 in a somewhat altered form as follows (Bulletin 36, page 120) : 



1. Strips are always one chain (66 feet) wide. A section invariably 

 comprises one acre equaling i x 10 chains. 



2. The measuring tape is trailing in the center of a strip; two caliper 

 men (proceeding one at the left, the other at the right hand of the tape) 

 caliper a belt one-half chain wide, estimating the width at either side 

 of the central tape. 



3. The compass man or tally man with the^ front end of the tape 

 attached to his belt goes ahead and stops at the end of every chain, 

 allowing the calipers to catch up. 



4. Thus there are ten stops for every acre; after 10 chains the tally 

 man enters general notes. 



5. Heights may be measured by a separate crew. 



A crew of four men calipers in merchantable timber 20 to 40 acres 

 per day; in small and merchantable timber from 15 to 25 acres per day; 

 in longleaf pine up to 65 acres per day. 



PARAGRAPH LXII. 



FOREST RESERVE METHODS. 



Roth's Forest Reserve Manual gives three methods of valuation sur- 

 vey, No. i and No. 2 being sample-area-methods, and No. 3 an entire- 

 area-method. 



i. Sample circles with a radius of 20 yards, the circle containing 

 J4 acre; the radius is estimated, or paced from a central stick. Two 

 sub-methods are permitted, namely: 



a. Count the number of trees of merchantable size; estimate the aver- 

 age tree according to log length, taper and thickness of bark; estimate 

 the percentage of defectiveness (from 10% to 40% after Manual, page 49). 



