72 SAMPLE PLOT STUDIES 



Illustration III. — The Volume Curve Method. 



Principle. — This method differs from all others in that no determination of 

 average trees is necessary. The underlying principle depends upon the 

 construction of a volume curve based on D.B.H. made from a few trees 

 selected so that the small, the medium and the large sized trees are repre- 

 sented. 



Directions: 



A. Parlies and Equipment as in Illustrations I and II . 



B. Method of Procedure. 



1. Use the same area and the same sample plot with its tree measurements 



as in Illustrations I and II. 



2. Select 6 sample trees without reference to any particular diameter but 



apportioning them so that the large and the small trees will be 

 represented, and so that in a measure the diameters for which the 

 largest number of trees have been recorded will be given the largest 

 number of sample trees. 



3. Fell the sample trees, and determine their total cubic foot contents, 



without bark, by means of ten-foot sections. 



4. On a sheet of cross-section paper now plot the volumes of the sample 



trees on their diameters (D.B.H.) . Draw a smooth curve, and 

 read off a table of volumes for diameters in whole inches. 



5. Apply the volume table to the measurements of the trees on the plot 



to determine the contents of the whole plot and from the latter the 

 contents of the tract. 



C. Discussion. 



1. Comment on the three methods giving your views on the advantages 



and disadvantages of each with reasons. 



2. Outline methods of procedure for the Urich and for the Draudt 



methods. 



3. What per cent of a tract should be measured to insure a good estimate? 



PROBLEM 34. (Field.) The Determination of the Rale of Growth in 

 Even-aged Stands by the Analysis of Felled Sample Trees. 



Explanation. — This exercise endeavors to illustrate in a practical manner 

 the chief problems in growth in even-aged stands that may be solved by 

 means of felled sample trees. As the details of the method of procedure 

 have been illustrated in connection with previous problems the student should 

 be able to carry out the work of the accompanying illustration from very 

 general directions, and the directions in the Method of Procedure have been 

 so made. The scheme will serve, in addition to illustrating the problems 



