Forest Mensuration 63 



2. On land cut over n years ago, find by valuation survey and stem 

 analyses : 



a. The present volume "F." 



b. The volume "y" of the trees now standing as it was "n" years ago 

 with the help of tree volume tables. 



c. From the stumps the volume "x" of the trees logged "n" years ago. 



3. A product of "F" units (with an undergrowth not fit for logging) 

 has been derived in "n" years from an original stand aggregating "y" 

 plus "x" units of volume. 



4. Grouping hundreds of sample plots together, yield tables for local 

 use are obtained. Misleading is, of course, the multiplicity of conditions 

 (mixture of species, soils, original stands, pasture and fire) surrounding 

 a second growth which check the applicability and the combination of 

 the tables found. 



The tables are way signs, not ways, toward a true knowledge of the 

 productiveness of cut-over woodlands. 



PARAGRAPH XCVI. 



YIELD TABLES OF THE BUREAU OF FORESTRY. 



Bureau yield tables are meant to show the growth on cut-over land 

 occurring within the next 10, 20 or 30 years, if a tract is logged to a 

 10", 12" or 14" (or any other) limit. Bureau yield tables are based on 

 tree volume tables and on an account of the numbers of tree individuals 

 found in the various age classes of forest, viz., diameter classes of trees. 



The influence of the different qualities of soil on tree growth is not 

 given, only one average volume table being constructed. The volume 

 tables show the number of years which a tree requires to increase its 

 diameter b. h. by one inch. The volume tables record, in addition, the 

 volume increase corresponding with such diameter increase. Applying 

 these findings to the stumpage presumably left after logging, the volume 

 can be ascertained which is expected to be on hand 10, 20 or 30 years 

 later. The volume growth is forecasted, as if it were taking place under 

 primeval conditions. 



The Bureau neglects entirely the death rate of trees, due to natural 

 causes and especially high amongst seedlings and saplings, or else due 

 to the logging operations themselves. The results forecasted in this way 

 must be invariably too high. 



Pinchot's Spruce Tables (The Adirondack Spruce, p. 77) are based on 

 similar premises : 



a. Construct volume tables by stem analysis (stump-analysis) on land 

 cut over for a second time, thus showing rate of growth for trees left 

 standing at the first cut. 



b. Construct tables, by actual measurements in the woods, giving the 



