SAMPLE PLOTS I^ T SILVICULTUKAL RESEAKCH 85 



87. In cases where the ultimate height is used for site-classification pur- 

 poses, ultimate-height values should be correlated with the height at the 

 classification age, and the site-index number obtained thereby. In other 

 cases this should be done wherever practicable, as an aid to application of 

 the tables. 



88. A summary should be prepared for each plot for all species, showing the 

 basal area, number of trees, volumes in cubic feet and board feet. The fore- 

 going should be for all trees on the plot. The same information should be 

 summarized for the dominants, and, in addition, the average basal area per 

 tree and the average height corresponding thereto. 



89. Compute the number of trees, and the average basal area and corres- 

 ponding average height for the trees above the diameter limit fixed by the 

 board-foot volume table which is to be used. 



90. Compute the plot area and express all summarized figures on a per acre 

 basis. 



91. The rejection of plots should be based primarily on deviations in basal 

 area from the tentative curves of basal area over age and site. 



92. For this purpose preliminary curves should be prepared of basal area 

 on age by site-index classes, and the deviation of each plot from these curves 

 computed, interpolating to the nearest year of age and nearest foot of site 

 index. The standard deviation should then be computed (using the approxima- 

 tion formula 1.25 AD—SD) and all plots deviating by more than two standard 

 deviations should be rejected. 



93. The remaining plots should be sorted by age and site-index classes. The 

 classes should be 5, 10, or 20 years in age, depending on the range of ages, 

 and 5, 10. or 20 feet of site index, depending upon the range of site indexes. 



94. For each class the following totals should be computed : Number of 

 trees per acre, and volume per acre in board feet and in cubic feet. The average 

 basal area per tree should then be obtained by dividing the total basal area 

 per acre by the total number of trees per acre. The average height should be 

 obtained by giving each plot equal weight. The foregoing figures should be 

 obtained for the entire stand, for the dominant stand, and for that above the 

 diameter limit fixed by the board-fo<U volume table used. 



95. In preparing these figures the plots should be given equal weight by 

 using the per acre figures. 



96. Harmonized curves should be prepared by site-index classes over age for 

 each element mentioned in paragraph 94. Many of these curves may profitably 

 be developed by means of anamorphosis. 



97. Curves of average basal area per tree should be substituted for those 

 of average d.b.h., the final results being translated into terms of diameter for 

 entry in the tables. 



98. The following checks should be used: (1) The number of trees per acre 

 times the average basal area per acre should equal the total basal area per 

 acre ; (2) the number of trees per acre times the volume from the volume 

 table corresponding to the average diameter and height should equal the aver- 

 age volume per acre. Both these checks should be applied to the entire stand 

 and to the dominant stand. Check no. 2 should be applied to both the board- 

 foot and the cubic-foot curves. In addition, the board foot-cubic foot ratio 

 when plotted over d.b.h. should produce a single curve of normal shape for 

 all site-index classes. Furthermore, the percentage ratio between the total- 

 stand and dominant-stand values for all factors when plotted over the average 

 d.b.h. of the entire stand should produce a well-defined curve of reasonable 

 shape. Lastly, for all factors, the aggregate difference between the actual 

 measurements and those indicated by the curves should not exceed 1 percent. 



99. Average deviations of the individual plots from the curves should be 

 computed for the following factors : Basal area per acre, number . of trees 

 per acre, volume board measure per acre, and volume in cubic feet per acre. 



100. The frequency distribution of the diameter classes should be investigated 

 and if the normal distribution is found, the standard deviation should be 

 curved over average d.b.h. This will permit the preparation of stand tables 

 for any age and site. 



101. Even if this frequency distribution is not normal, the existence of any 

 characteristic type will permit the preparation of subordinate tables (such as 

 trees above 4 inches d.b.h.), by curving the ratios between the factors for the 

 stand above such a limit to those for the entire stand over the average d.b.h. 





