Forest Mensuration 61 



Remarks on a: 



The contents and age of all woods (normal) surveyed are plotted in a 

 diagram, the age forming the abscissa and the volume the ordinate of the 

 system. 



Curves are then drawn outlining the maxima and minima of growth 

 observed. 



The horn-shaped space between these curves is divided into a number 

 of sectors equal to the number of yield classes to be distinguished. The 

 middle line of each sector illustrates the productiveness of its class. 



The average height growth is obtained in a similar way, the height data 

 forming the ordinates in a system of co-ordinates. 



Baur finds that the allotment of a given plot to a volume-sector corre- 

 sponds with its allotment to a height sector. In other words, the height 

 is, after Baur, an absolutely reliable indicator of the quality of the soil, 

 or, what is the same, of the yield class. 



The growth of sectional area, height and volume being known, the 

 development of the form factors for the various sectors is readily ob- 

 tained from the fraction 



sXh 



Remarks on b: 



An analysis of the average stems in lots surveyed would not throw 

 any light on their connection as members of one and the same chain 

 of observation. After Robert Hartig, the 200 strongest trees are analyzed. 

 After Wagener, the ideal cylinders merely of these 200 strongest stems 

 are analyzed by ascertaining their height growth and their diameter 

 growth at breast height. Weise and Schwappach are satisfied with an 

 analysis of the heights merely of the 200 best stems. 



The selection of sample plots is not easy, even in second growth raised 

 under forestal care. A valuation survey establishes for each plot the 

 number of stems and the sectional area for each diameter class of stems 

 (usually divided into 5 classes) ; further, the average age and the average 

 height of the plot. The volume is then figured out, usually, according 

 to the Draudt-Urich method. 



The experiment stations maintained by the European Governments 

 control the growth of a large number of experimental plots, which should 

 not be smaller than y 2 acre each. 



The sample plots are corner marked, and, more recently, the individual 

 trees contained therein are numbered consecutively. Surveys of these 

 plots are made every five years. The point of measurement is indicated by 

 a chalk line. 



In America normal sample plots have not been established as yet by 

 the Bureau of Forestry in second growth. The sample plots at Biltmore 

 do not represent a normal second growth. 



