66 BULLETIN 1402, U. S. DEPARTMENT OF AGRICULTUEE 
seed trees selected mechanically through the device of a diameter 
limit, supplemented by occasional larger trees. Cutting to a diam- 
eter limit does fairly well in obtaining good distribution of trees, 
but catches some poorly formed, old, and suppressed trees, misses 
some fine thrifty young individuals, and on part of any cut-over 
area leaves openings with no trees. 
Better practice for producing full timber crops must depend on 
individual selection of trees to be left. It must, moreover, be based 
on the same treatment of all species found in virgin forests ; and on 
the selection of reserved trees primarily on the characteristics of the 
individual trees. Three seed trees per acre, carefully selected, will 
be at least as effective as four per acre mechanically selected by 
diameter-limit cutting. 
The most rapid growth and most effective seeding will be obtained 
when the reserved trees are selected and marked by a forester or 
experienced woodsman, familiar both with logging requirements 
and the characteristics of desirable trees. 
SELECTION OF SEED TREES 
As already noted, a " seed tree " is a healthy, uninjured tree of 
over 18 inches diameter ; that is, of a size that can be counted on to 
produce seed immediately after the area has been logged. As size 
increases cone production per tree also increases, a 26-inch tree pro- 
ducing, on the average, about three times as many cones as an 18-inch 
tree, though at greater cost in board feet per thousand seeds. 
A study in Arizona {10) showed clearly that the germination per- 
centage of seed from blackjack trees was uniformly higher than that 
from the older yellow pines, and that for trees of the same size the 
blackjack produced more seed than the yellow pine. Therefore, for 
seed production, as well as for rapid growth, thrifty young trees 
should be reserved wherever available. 
Where no thrifty young seed trees are present, intermediate trees 
or, very occasionally, typical mature pines must be kept. Similar 
conclusions apply to other species, though much less study has been 
devoted to sugar pine and the firs than to yellow pine. 
NUMBER OF SEED TREES REQUIRED 
Study of carefully marked national forest cuttings in different 
types makes it fairly certain, as shown on page 40, that an average 
of three seed trees per acre, carefully selected, both for their indi- 
vidual characteristics and their distribution, will be sufficient for 
restocking. 
As shown also, the number of young and thrifty trees present is 
smaller in the East Side yellow pine type than in most other timber 
types, including the mixtures of yellow and sugar pines, Douglas 
and white firs, or any two or three of them. On national forest 
cuttings, in mi±ed types, as many as 20 or 25 thrifty young trees 
per acre are left after cutting, the great majority of which are re- 
served for growth, not for seed production. 
In the great majority of cases thrifty trees selected for growth will 
serve also as seeders. Only in case no such trees are available on a 
particular area will it be necesary to reserve trees solely for seeding 
purposes, 
