Notes on Winterkilling of Forest Trees 45 



the younger trees which were defoliated but whose branches 

 were not killed, Murdock considered the growth of 1909, both 

 in diameter and length, to be normal. In most cases seen by 

 the writer, length increase in such trees was practically nor- 

 mal, but in part of them it did not seem normal. Neverthe- 

 less it is noteworthy that complete or nearly complete de- 

 foliation of four years' growth of pine needles should have no 

 distinct effect on the growth of the following season. It would 

 be interesting to determine if more decrease of the growth of 

 1910 than of 1909 was caused by the chinook. 



All of the above observations are on Pinus ponder osa. 

 The only other conspicuous conifer near Deadwood is the 

 Black Hills Spruce (Picea canadensis). This grows on the lower 

 and moister sites, near the streams. Injury occurred to those 

 exposed, but the Spruce appeared to the writer to be fully 

 as hardy as the Pine in the places where they grew side by 

 side, so that comparison was possible. No Spruce which was 

 killed entirely was seen by the writer in the vicinity of Dead- 

 wood or along the C., B. & Q. railroad to the south of Dead- 

 wood. 



In the case of the Spruce the type of injury was quite 

 different from that of the Pine. Instead of the needles of 

 certain ages being killed, the branches or branchlets which 

 were most shaded or were growing least vigorously were killed 

 outright, while on parts of the tree there was no damage to 

 needles of any age. 



On the hills where the Pines were injured are also small 

 Birch and Aspen trees. Injury to these toiok the form of killing 

 back the latest growth, with the consequent formation of water- 

 sprouts. The Birch seemed to be rather more easily injured 

 than the Pine, while the Aspen was less susceptible than Pine. 



The data available as to the exact weather and soil con- 

 ditions prevailing in this case of chinook winterkilling, and 

 detailed knowledge of the way in which winter injury works, 

 are so incomplete that it is impossible to do more than guess 

 at the factors concerned in the present instance. Why the 

 higher sites and the northerly exposures were the most injured 

 there is no way of telling, though exposure to wind was prob- 

 ably an important factor. The great ranges of temperature 

 recorded, between 42 and 52 degrees on a number of days, 



