UTAH ACADEMY OF SCIENCES 53 
their removal does not injure the soil and lessen the chance 
for reproduction. As many as possible of the diseased 
and dwarfed trees should also be marked. In the average 
virgin forest an improvement cutting is the one first 
needed. The aim of this cutting is to leave the forest with 
an even stand of well distributed thrifty growing trees. 
Thinning is another problem of intensive forestry. It 
is concerned with immature stands while improvement cut- 
tings are made in mature stands. The aim of thinnings 
is to keep the stand in the younger stages at the greatest 
rate of growth without deterioration of the form or quality | 
of the trees. In mixed stands the better species are favored 
so far as possible. In detail thinning is an intricate prob- 
lem and has been much elaborated in Europe. They are, 
however, too expensive to be applied in this country at the 
present time, although information derived from a study 
on a small scale, will be useful later. 
The substitution of valuable foreign forest tree species 
for less valuable native ones is another important problem. 
While great care is necessary and not too much should be 
expected, yet there is some chance of success. The 
Eucalyptus in certain parts of California and the Norway 
Spruce in the Adirondacks are examples. In the latter 
locality it is expected that the foreign spruce will eventually 
take the place of the native red spruce because of its more 
rapid growth and consequently shorter rotation period. 
Douglas Fir has been introduced from this country to 
Germany where it is valued highly and stands almost old 
enough to yield seed have been produced. White Pine, 
the great lumber tree of Michigan, has also been introduced 
into Germany much earlier and stands 150 years old are 
now seen. 
In this successful interchange of foreign and native 
species there is much encouragement that patient and per- 
sistent effort in this line will increase the value and use- 
fulness of our forests. 
TO SUMMARIZE. 
1. In order to insure forestry, fires must be reduced 
to the minimum through eliminating the causes and being 
