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



applied to normal or rapidly declining infestations, as the operation 

 of natural-control factors in such cases is more effective than artificial 

 measures. 



The next step is to make an extensive survey of the area to deter- 

 mine what parts must be included in the control program, the num- 

 ber of trees that will require treatment, and the probable cost of 

 the work. This extensive survey is usually made by experts in 

 forest-insect control who have had experience in estimating bark- 

 beetle losses and planning control campaigns. 



The methods to be used in such work will depend on the character 

 of the country, the size of the area involved, the degree of accuracy 

 desired in the results, and the time and money available for the 

 work. The simplest and least expensive type of survey is made by 

 viewing the country from lookout points and making counts along 

 roads. Sample strips run at intervals back and forth across infested 

 areas give a very comprehensive estimate of the amount and distri- 

 bution of infestation, and where time and money are available these 

 unquestionably furnish the most satisfactory basis of estimates. The 

 cruising of sample plots has its place as a supplement to topographic 

 viewing, and with small units it is often possible actually to survey a 

 rather large percentage of the area in this way. 'Wliere large areas 

 of diverse topography include a number of different forest types, 

 several different estimation methods or combinations of methods may 

 be used. In fact, every source of information should be utilized in 

 arriving at the final estimate, and the more survey data at hand the 

 more accurate will be the final result. 



The topographic method 



The topographic method, or red-top survey, is particularly well 

 adapted to estimating bark-beetle losses over large forested areas of 

 rough topography, where a large part of the forest can be viewed 

 from open valleys, ridges, or lookout points. It is the cheapest and 

 quickest method but is subject to a high degree of error unless sup- 

 plemented by intensive examinations of sample plots or strips, in 

 which case fairly reliable results can be obtained. 



In using this method, the estimator, equipped with binoculars and 

 a topographic map of the area, travels through the area visiting all 

 of the ridges, valleys, or lookout points that can be found. At each 

 selected point the opposite slopes and visible areas are viewed, the 

 red, sorrel, or fading trees counted, and an estimate placed on the 

 map as to the total number of dying or dead trees per acre. Then 

 strips or plots are actually cruised and a ratio determined between 

 the number viewed and the total number acutally found. Also, the 

 relative proportion between newly infested and abandoned trees, all 

 of which have been counted in the general red-top survey, is deter- 

 mined. The total estimate is then corrected by these ratios. 



The saTnple-strip method 



The sample-strip method is adapted to estimating bark-beetle 

 losses on flat or gently rolling areas where viewing from a distance is 

 impossible. It is also a more efficient and accurate method and can 



