46 Forest Club Annual 



and 75 degrees on January 8, would seem sufficient to cause 

 much injury. However, the mere fact that the temperature 

 went so low following warm days is hardly sufficient explana- 

 tion, because a temperature 15 degrees below zero probably 

 freezes cell sap little more than would a temperature of fifteen 

 degrees above zero. The conditions probably most important 

 in causing injury appear to the writer to be these : that after 

 a temperature many degrees below zero, a strong warm wind 

 from the northwest sprang up on January 8, with the temper- 

 ature rising to 57 degrees. This must have resulted in fairly 

 rapid loss of water from the needles in parts of trees exposed 

 to this wind, while the trunks and even the branches were 

 still frozen solid. The slender supply of w r ater in the needles 

 and the smaller twigs would manifestly be unable to stand 

 much transpiration loss, when it could not be replenished from 

 the larger stems. The killing might of course have been the 

 cumulative effect of the transpiration of the three days, Jan- 

 uary 7, 8, and 9, throughout w r hich the larger parts of the 

 stems could not have been really well thawed out at any time. 

 However, northwest exposure seems to have been very im- 

 portant in determining the location of injury, in this part of 

 the Forest. 



On January 8 a strong wind is recorded in the same part 

 of the Forest. In view of these facts, it is likely that the 

 conditions prevailing January 8 were at least the most im- 

 portant factors, even if not the only ones, in causing this 

 injury. 



At the Fremont Experiment Station, near Pike's Peak, 

 Colorado, at an altitude of 9,000 feet, the same type of injury 

 occurred to Pinus ponderosa as in the Black Hills. It was not 

 severe enough to have any serious results. At slightly lower 

 altitudes at Pike's Peak, White Fii( Abies concolor)-was also in- 

 jured during this same winter, the type of injury in this case be- 

 ing the same as described for Picea canadensis in the Black Hills. 

 Information secured chiefly from Dr. G. G. Hedgcock makes it 

 appear that chinook injury occurred at certain altitudes in 

 many places from the Black Hills west into Oregon, and in 

 this territory is commonly referred to as "Red Belt." Dodge- 

 pole Pine was also considerably injured in these localities, 

 though not so badly as Yellow Pine. It is expected that Dr. 



