2-i JOl-RXAI, OF I'ORIvSTRV 



the trees on the area for each separate year for a period of 20 years 

 was desired. 



THE IXIXUKXCU OF TIIIXXIXG ON WESTKRX lIli.MLOCK IXFECTED WITH 

 ECHINODONTIUM TINCTORIUM 



It is evident that the various environmental factors tend to influence 

 the vigor of the tree, and the vigor in turn presumably determines the 

 ability to resist fungous attack. The part which light i)lays in the full 

 development of a tree is important, although, according to Zon and 

 Graves,^ there are other factors concerned in the production of in- 

 creased increment due to the opening up of a stand. The process of 

 thinning has always been used with the belief and justified by the ex- 

 perience that the remaining trees left standing would show an appre- 

 ciable increase in development soon after the stand was opened to more 

 light and upon the establishment of less root and crown competition. 

 The principal effect to be noted in the development of the trees so 

 favored is a marked increase in the amount of wood laid down annually. 

 This physiological reaction is a direct indication of the increased vigor 

 of the tree and is a means by which foresters are able to judge the 

 alternate periods of low and high vigor. With the purpose of record- 

 ing the effect that thinning has upon western hemlock and grand fir 

 infected with EcJiinodontUtui tinctorimn, the following data were se- 

 cured. The field data were grouped under the two tree species and 

 separate tables composed accordingly. 



The data on western hemlock were concentrated by means of aver- 

 ages, totals, etc., into one table, and from that portion of it which gives 

 the average width of the annual rings a curve was platted (fig. i). 

 This curve serves to show graphically the marked effect produced by 

 the opening up of the stand. From the various plots examined a total 

 of 57 hemlock were analyzed, ranging in age from 48 to 116 years, and 

 giving the average age for the stand at approximately ^2 years. The 

 hemlock curve (fig. i) shows a slight suppression period between the 

 years 1897 and 1899, followed in 1900 by a slight rise. In 1902 the 

 curve drops to its lowest point, and seems to indicate the effect or shock 

 of the sudden opening of the stand, with its attendant injuries to vari- 

 ous portions of the tree. The unusually large amount of logging in- 

 juries, including stripping of live branches from the trunks and injury 

 and exposure to the root system, were successfully healed by the in- 

 creased activity of the trees. In 1903, the year following the close of 



'Loc. cit. (i). 



