TIMBER GROWIIs^G AND LOGGING PRACTICE IN CALIFORNIA 39 
seed trees, the land will remain unproductive for many decades. 
In all cases, though reproduction from seed trees is generally slow, 
it must be relied on to complete the restocking of cut-over lands. 
Under present conditions no alternative is possible. 
It is obvious at the start that in planning to leave trees for seed 
the selection of small trees is desirable, for the higher values in 
the large trees would render their reservation costly to the operator. 
It is further evident that some mechanical form of selection of these 
trees will be the most suitable, for the selection must be made in the 
process of cutting and by woods labor and camp foremen. Estab- 
lishing a diameter limit for cutting is, for the purpose of simple 
timber-growing measures, a logical and usable system, primarily be- 
cause it is already in use on most operations and can readily be 
applied CA^erywhere. 
The problem, then, is to determine the number of seed trees per 
acre that will be necessary to insure stocking of cutting areas with 
the least alteration of existing practices and the least additional 
cost, and also the diameter limit for all species that will most nearly 
provide the number of trees desired. 
The solution of the problem involves an answer to several 
questions : 
(1) What is a seed tree? 
(2) What number of seed trees is required for restocking? 
(3) Are small seed trees available in different forest types? 
(4) How many seed trees are left in current cutting practice 
on private lands? 
(5) What is the simplest method of preserving seed trees? 
(6) How large an investment is required to provide seed trees? 
WHAT IS A SEED TREE? 
The first essential is to leave trees of a size that can be counted 
on to produce seed irmnediately after cutting, for then seedlings 
establish themselves more readily than after brush has invaded the 
ground. Within what diameter limits this may best be accomplished 
is indicated by general observations on many sample plots and cut- 
over areas, and more particularly by detailed study of cone produc- 
tion on two permanent sample plots in the east slope yellow pine 
tj^pe. It was found that the percentages of trees in each diameter 
class bearing no cones, which at 10 inches is 100, drops rapidly, 
reaching 8 per cent at 18 inches and zero at 20 inches. The percent- 
age of trees producing a light crop rises rapidly, reaching the peak 
with the 16-inch class, and then drops more gradually, reaching the 
zero point at 32 inches. Trees producing a medium crop first 
appear at 18 inches, increase to a peak with the 28-inch class, and 
then drop. Trees producing a heavy crop do not show up till a 
diameter of 28 inches is reached, after which the curve appears to 
be essentially the same as for the other categories. The study in- 
dicates that yellow pine trees 18 and 20 inches in diameter have con- 
siderable cone production, whereas smaller trees bear at best only a 
light and uncertain crop. In the Southwest, Pearson has found 
that yellow pines smaller than 20 inches in diameter are ineffective 
seed producers {10). 
On certain of the yellow pines studied, the cones per tree were 
counted. Though the data are not wholly conclusive, they confirm 
