4 CIRCULAR 3 3 3, U.S. DEPARTMENT OF AGRICULTURE 



TYPES OF SAMPLE PLOTS 



For the purposes of this circular, the following plot definitions 2 

 are adopted: 



Permanent sample plots are small representative areas on which 

 developments are followed by means of repeated measurements or 

 examinations continuing through a period usually exceeding 10 years. 



Temporary sample plots are similar areas on which measurements 

 are taken or conditions examined at the time of plot establishment 

 with no intention that subsequent developments on them shall be 

 studied. 



Semipermanent sample plots are those on which measurements of 

 stand conditions are taken, but where the development of the indi- 

 vidual trees is not followed in subsequent remeasurements. 



A subplot or quadrat (pi. 1, A) is a small division laid out 

 within a sample plot for the purpose of studying reproduction or 

 other vegetation too abundant to be studied on the whole sample 

 plot, or for the purpose of studying the effect of special conditions 

 or treatments. 



A plot section is a major division of a sample plot laid off to facil- 

 itate numbering and mapping the trees and as a means of using data 

 from different parts of the plot separately. 



Control plots are permanent sample plots so established as to form 

 a base or norm to which the response of treated plots may be ref- 

 erenced. 



Untreated plots are permanent sample plots established for the 

 purpose of following through the life of a stand influenced only by 

 natural factors. 4 



In every study involving a comparison of treatment with no 

 treatment, it should be remembered that " no treatment " is in fact 

 a special case of " treatment " and that control plots are just as 

 important as any of the treated plots, and subject to the same rules. 



PRELIMINARY CONSIDERATIONS 



QUALIFICATIONS OF THE INVESTIGATOR 



Correct establishment of sample plots is not such a simple matter 

 as many foresters believe. It requires thorough preparation, a high 

 degree of skill, and a knowledge of many requirements and many 

 dangers involved. Any man undertaking to establish sample plots 

 for use in silvicultural research should first of all have imagination, 

 thoroughness, and accuracy; should know and appreciate the prob- 

 lem at hand: should understand the specific factors involved: 

 should be acquainted with the literature of his general problem and 

 with work being done upon the problem: should be familiar with 

 the region and type in which the work is to be done; and should 

 have a rudimentary knowledge of statistical methods. Of these 



2 Further explanation of terms used in the circluar may be found in definitions adopted 

 by the Society of American Foresters (25).* 

 " 3 Italic numbers in parentheses refer to Literature Cited, p. 62. 



4 The classification " untreated plots " covers growth or yield plots which are 

 established in overstocked, normal, or understocked stands in order to determine such 

 matters as the application of yield tables, the progress of growth, or mortality. A 

 much larger number of these growth plots than has been established in studies thus 

 far undertaken appears to be needed to cover the range of sites and of stocking 

 commonly found in our present immature forests. 



