FACTORS DETERMINING WIDTH OF STRIPS 275 



strips per forty, each 10 rods wide, covering 25 per cent of the area was abandoned 

 in favor of the use of a narrower strip 6J rods wide to increase the accuracy of the 

 estimate on the strip. The number of strips was then doubled, or four strips run 

 per forty, and the total per cent of the area estimated was thus increased from 

 25 per cent to 33§ per cent. If, instead, the number of strips had been kept the 

 same, but the width of each strip increased to 20 rods, a lesser degree of accuracy 

 would have been attained in spite of an increase to 50 per cent of the area covered. 



In determining the number of strips required for a forest survey, 

 the character of the topographic map desired must be considered with 

 reference to the topography. Lines run \ -mile apart will give only a 

 rough scale map in bold mountainous topography. Lines placed at 

 J-mile intervals in mountainous slopes with large features, are sufficient 

 for an accurate topographic map with a large contour interval of from 

 50 to 100 feet. On all flat or gently rolling forested slopes with no 

 outlook, cut up by drainage or interspersed with swamps, it is impos- 

 sible to make an accurate topographic map with proper contour interval 

 of from 10 to 20 feet and show all details of drainage and slope, unless 

 lines are run at f-mile intervals, but this interval is sufficient for all 

 maps on the ordinary scale of from 2 to 4 inches per mile. Only for 

 a much greater detail will lines be required at less than this interval. 



The influence of the forest cover upon the number of strips required 

 for accuracy increases with the two factors, density of the forest cover 

 and variation of the timber, whether caused either by age, size or diver- 

 sity of species. Finally, the increasing value of the timber from any 

 cause, whether through quality or unit price, will require an increase 

 in the per cent of area covered, which means a greater number and 

 more closely spaced strips. 



These conditions frequently require a full or 100 per cent estimate 

 by forties, the best examples of which are the heavy stands of rapidly 

 increasing value in the Pacific Coast States, or stands of large mature 

 hardwoods with great variety in size and value. 



The width of strips is determined by the accuracy with which this 

 width can be measured by the eye and the dimensions of all the trees 

 standing thereon ascertained, or the timber upon it measured and 

 counted. This width is diminished directly by the amount of brush 

 and undergrowth which obstructs the vision. In brushy country, strips 

 seldom exceed from 4 to 6| rods. The width of a strip is also diminished 

 by decreasing size and increasing number of trees on the strip. In 

 young timber, with many stems per acre, a greater degree of accuracy 

 is obtained on a 4-rod strip accurately measured and counted than 

 upon a strip of twice the width. Conversely, open and large timber 

 with fewer and more scattered trees and an unobstructed view not 

 only permits a wider strip to be measured accurately, but requires an 



