Methods of Forest Organization. 65 
especially in mountain districts, produced very unequal 
felling budgets. To overcome this inequality, Jacobi, in 
Goettingen (1741) introduced proportional felling areas, 
making the felling areas on poor sites permanently 
larger. 
Similarly, v. Langen and Zanthier attempt equal 
annual returns, without slavishly holding to the geomet- 
Tic division, only seeing to it that the total area be cut 
over in the predetermined rotation. 
The first attempts to introduce a regulated manage- 
ment by making a volume division the basis is recorded 
in the Harz mountains in 154%. This method based on 
very crude estimates, although upon very fair forest de- 
scription, was continued into the 18th century. 
In the last half of the 18th century all these crude 
methods were improved and applied on extensive areas. 
In 1785 Zanthier combined area and volume division, 
determining the felling budget on each felling area by 
counting and estimating the trees and calculating how 
many trees could be used annually under a sustained 
yield management; the area division being used only as 
a check or means of control. 
A very considerable advance was made by Oettelt, 
(who surveyed and regulated the Weimar forests in 
1760) in the elaboration of details and establishment of 
proper principles for regulating the felling budget. 
In his forest description he introduces for the first 
time periodic age classes, usually six, but of uneven 
length: Young growth below twelve years, thicket twelve 
to twenty-four years, polewood twenty-four to forty 
years, clear timber forty to fifty, medium timber fifty to 
seventy-five, mature timber seventy-five and over. 
