TIMBER GROWING AND LOGGING PRACTICE IN CALIFORNIA 41 
The data also indicate that where it is desired to reserve the 
smallest practicable trees and the minimum number of them as seed 
trees, by mechanical rather than by individual selection, this may 
be accomplished by cutting down to a general diameter limit of 
20 inches. (Fig. 15.) The trees caught within this limit will 
be capable of producing seed regularly and will at the same time 
afford the largest cone production per unit of volume. They will, 
however, be spaced irregularly, particularly in the pure yellow 
pine type where the pines tend to occur in groups. Also the 
quality of the trees as seed producers will unquestionably be lower 
than when such trees are individually selected. To compensate 
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Fig. 15.— DIA^IETER LIMIT CUTTING LEAVES LAND PRODUCTIVE 
In the mixed conifer type, here shown, cutting to a minimum diameter of 
20 inches leaves ample small, thrifty trees that will furnish seed and at the • 
same time make rapid growth toward a second, intermediate cutting. In most 
of the types this holds true, pure yellow pine being the most conspicuous excep- 
tion. Land in this condition is an asset to the owner. 
for these disadvantages, a minimum of four small seed trees will 
be needed under the diameter-limit method of selection to attain 
the same degree of restocking of cut-over lands that three trees 
per acre individually selected will make possible. 
The specific data cited do not form the only basis for selection 
of 20 inches as the diameter limit for cutting, or four trees per 
acre as the minimum number necessary ; but they are given in detail 
as being representative, and examination of seed production and 
seed trees on many cut-over areas confirms the conclusions. Trees 
smaller than 20 inches are occasionally found bearing good crops 
of cones, and in some cases fewer than four trees per acre appears 
to be sufficient for restocking; but for a general working average 
those limits are justified. 
