Notes on Winterkilling of Forest Trees 43 



In at least one case depth of soil could not have had any 

 influence. Adjacent trees, some growing in soil four feet deep, 

 and others in soil a little over one foot deep, were equally 

 injured, or if any difference could be said to exist, it was in 

 favor of the shallower soil. 



In the vicinity of Deadwood, close stands of reproduc- 

 tion, 5 to 7 feet in height, were so badly injured that more 

 than half of the trees in a patch ten or fifteen yards square 

 were killed. In general, trees of this age were more severely 

 injured than mature trees, when the two ages were on the 

 same site. However, since a relatively greater part of the 

 reproduction is on the lower slopes, the proportion of injury 

 in the younger stands was probably no greater than in the 

 older ones. 



The most interesting thing about this type of winter- 

 killing was the uniform difference in susceptibility to injury 

 between needles of different ages. As one would expect, 

 where part of a single needle was injured, it was always the 

 part toward the tip, while the part near the base remained 

 healthy. Where a portion of the needles were injured, these 

 needles were always the older ones, while the younger needles 

 were unharmed. Where a tree was so severely injured that 

 only a few of its needles survived, these surviving needles 

 were sure to be those produced in 1908. If the tree was less 

 severely injured, the 1908 needles might all be in perfect 

 condition, the 1907 needles somewhat injured at the tips, 

 and the needles of 1906 entirely or almost entirely killed, 

 while all of the needles older than 1906 woiild be killed. In 

 cases of slight injury only the oldest one or two generations 

 of persisting needles were hurt. This means that the outer 

 needles of the trees, which were farthest from the water supply, 

 were always the ones which survived. Assuming that the 

 cause of death was transpiration during the sudden warm 

 periods indicated in the weather records quoted, it might fol- 

 low that the younger needles have a stronger pull on the 

 water supply than the older ones. This advantage of young 

 leaves over old ones in competition for water supply is seen 

 In herbaceous plants in the way drouth results in the wither- 

 ing of the older leaves while the younger leaves still seem 

 healthy. That somewhat the same difference in water obtain- 



