THE MEASUREMENT OF PERMANENT SAMPLE PLOTS 313 



uniform conditions and their size should be governed, first, by the 

 possibility of securing this uniformity and second, by the expense of 

 measurement which limits the size of the plot. Third, wherever 

 possible, there should be a control strip of exactly similar timber sur- 

 rounding the plot on all four sides in order to eliminate the influence 

 of different conditions of density or site around the borders of the plot. 



The merchantable timber on these plots is measured as follows: 



Tree Number. Each tree should be permanently numbered either 

 by white paint or by attaching a metal tag to the tree with a copper 

 nail. 



D.B.H. The point at D.B.H. is measured and spotted with white 

 paint or by the position of the tag. The D.B.H. is measured with a 

 diameter tape. 



Crown Class. The crown class is one of the following : 



re = trees standing alone; 



d = dominant; 



c = co-dominant; 



z = intermediate; 



s = over-topped, suppressed. 



Height. The height is measured to the nearest even foot with a 

 standard hypsometer. The Klaussner principle, which gives one 

 measurement, is preferred. ^ 



Forms are used which provide, for each tree, five vertical columns 

 in which to record the original and four subsequent measurements 

 which are taken at either 5- or 10-year intervals. 



The trees on such plots are usually numbered and measured indi- 

 vidually down to 4 inches, although in some instances 2 inches is 

 adopted as the basis for individual tree records. 



Immature timber below these sizes usually calls for smaller plots 

 which are sometimes laid out as subdivisions of a larger permanent 

 plot. The sizes of these plots are in proportion to the intensiveness of 

 the problem and the age of the timber. For determining the conditions 

 which affect germination, plots from 10 to 20 feet square are large 

 enough. On these plots every seedling is counted and sometimes each 

 is marked by inserting a pin on which a tag can be attached. In this 

 way the mortality and survival of the seedlings can be later ascertained. 

 For the study of the development of reproduction, larger plots, up to 

 1 acre in size, are required. On such plots there is no effort to keep 



1 Some New Aspects Respecting the Use of the Forest Service Hypsometer, 

 Herman Krauch. Journal of Forestry, Vol. XVI, No. 7, p. 772. 



Comparative Tests of the Klaussner and Forest Service Hypsometer, D. K. 

 Noyes, Proc. Soc. Am. Foresters, Vol. XI, 1916, p. 417. 



