24 BULLETIN 154, U. S. DEPARTMENT OF AGRICULTURE. 
stands may be blown down. As a rule, however, solid stands, even 
when overdense, are windfirm, provided they are of sufficient ex- 
tent—not narrower than the height of the trees. Light or even heavy 
thinnings can usually be made without danger of windfall by con- 
forming the operation to the height, age, and density of the stand, 
the character of the soil, and the exposure. 
Haphazard thinnings made on the Deerlodge Forest from 13 to 
25 years ago in the course of ordinary lumbering operations show 
a remarkably small amount of windfall. On only 2 of the 18 blocks 
examined was any windfall evident, and in each of these cases the 
stand had been very heavily thinned by the removal of 82 per cent 
of the original number of trees and 66 per cent of the cubic volume. 
On the remainder of the areas the stand was not so heavily thinned, 
though the cutting was heavier than would be considered advisable — 
in present-day Forest Service timber sales. In one of the early For- 
est Service sales on the Deerlodge Forest, on an area partly exposed 
and partly protected from the wind, where the soil was deep, fresh, 
and firm, a selection cutting removed about 40 per cent of the total 
number of trees and 59 per cent of the cubic volume. In the five 
years following the cutting only 3 trees out of the approximately 
5,000 left blew down. All of these were on the exposed portion of 
the sale area, and in each case a defective root system, due to fire 
injury, was the main cause of the fall. These and other observa- 
tions indicate the importance of removing trees with defective root 
systems. 
Another climatic factor which may cause damage to individual 
seed trees is sun scald. In many cases seed trees which have with- 
stood the wind for a number of years have died apparently as a result 
of too great exposure to sun. Owing to the thin bark of lodgepole 
the cambium on the insolated side of the tree is killed first. Many 
of the trees crack open on the sunward side before they die. The 
drying out of the ground when it is exposed to the sun probably helps 
to kill such trees. If trees are left so that their trunks do not receive 
full sun during most of the day, the likelihood of damage from sun 
scald is very small. ~ 
Frost cracks sometimes appear in lodgepole pine, and when they 
take a spiral form lessen the value of the tree for saw timber. Strong — 
winds sometimes open these cracks in a way to form large seams or 
checks which afford ready entrance for insects and fungi. _ The 
damage appears to be more prevalent in overmature than in younger 
stands, and is more often encountered in Wyoming and Colorado 
than in Montana. Frost may also cause injury by heaving 1 or 2 
year old seedlings out of the ground. 
Snow, accumulating on the tops of lodgepole trees 4 inches or 
less in diameter, especially when in dense stands, often bends the 
; 
? 
| 
