230 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



sorrel, or red-top trees are counted within a specified distance 

 on either side of the line of travel. 



The width of the strip will depend on the density of the forest 

 stand, and should be so chosen that the outer edges will cor- 

 respond approximately with the average limit of vision within 

 the stand. For open ponderosa pine stands a 10-chain strip (330 

 feet on each side of the center line) has been found generally 

 satisfactory, but in the heavier stands this often needs to be 

 reduced to an 8-, 5-, or even a 4-chain strip. In lodgepole and 

 western white pine stands, red-top surveys usually are limited to 

 5-, 4-, 2-, and even 1-chain strips. However, in these types exten- 

 sive surveys are usually conducted in the fall of the year to 

 determine the number of new attacks, and the old loss represented 

 by the red-top trees is ignored. Since the newly attacked trees are 

 not discolored and can be found only by sighting the pitch tubes, 

 very narrow strips are necessary, and a 1-chain strip (33 feet on 

 each side of the compass line) has been adopted as standard for 

 this work in the northern Rocky Mountain region. 



When a red-top strip count includes several ages of infested 

 and recently abandoned trees, it is necessary to examine a repre- 

 sentative series of trees, either on a sample strip or on a sample 

 plot, to determine the proportion of the different classes of insect 

 attack and years of infestation which may be represented. A 

 limited amount of intensive work is also necessary to determine 

 the average diameters, heights, and volumes represented by the 

 infested trees. The number of trees counted on the strips multi- 

 plied by the number of times the acreage of the strip would be 

 contained in the acreage of the entire area will give the approxi- 

 mate number of trees for the entire unit. 



No fixed rule can be given as to the portion of an infested 

 area that should be covered during an extensive insect survey to 

 obtain a reasonable degree of accuracy. The exactness of the 

 survey will depend on the time and money available and the value 

 of the timber stand under examination. Small units of valuable 

 timber should be covered with a greater refinement of methods 

 and a higher degree of accuracy than an extensive area of heavily 

 infested lodgepole pine. Ordinarily 5 percent of an area should 

 give a reasonably good estimate for control purposes, and on large 

 areas a 1-percent sample is often sufficient. 



WHEN CONTROL MEASURES ARE ADVISABLE 



When the natural balance in a forest is disturbed and an out- 

 break of bark beetles threatens to destroy a large number of 

 valuable trees, the application of direct control measures (39) 

 is advisable provided effective methods are available and the 

 value of the timber that can be protected will justify the expense 

 of the work. Control measures are expensive and unless the 

 timber is valuable enough from the commercial, watershed-pro- 

 tection, or aesthetic standpoints to warrant the cost of control 

 measures, it is best to allow Nature to bring the epidemic under 

 control in her own way. 



To reach a decision certain data must be obtained. In the first 



