182 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 
applied to normal or rapidly dechning 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. Where 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 sample-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 
