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 



