22 



BULLETIN 722, U. S. DEPARTMENT OF AGRICULTURE. 



Table III. — Averajcs computed from field data relating to heart-rot in western hem- 

 loch based 2(po:i trees of the several age classes on plats of the river-bottom and south- 

 weslern-slo'>e t/^es. 





Num- 

 ber of 

 trees 

 (basis). 



Diam- 

 eter 

 breast 

 high. 



Height. 



Crown 



size 

 (height 



''y 



width). 



Crown 



rating. 



Lack 



of 

 vigar. 



Vr lumo 

 (cubic feet). 



R.t percentage. 



Type and age 

 classes. 



Total. 



Of rot. 



For 

 class. 



For stand. 





Total. 



In- 

 fected 

 trees. 



River-'bottom 



41 to 100 years. 

 lOltoieOyears 

 Slope type: 



41 1 J 100 years. 

 101 tol60 years 

 161 to 200 years 

 201 years and 



113 



7 



15 

 18 

 23 



25 



Incites. 

 5.9 



8.4 



8.4 

 13.6 

 17.5 



21.5 



Feet. 

 47.0 

 65.7 



62.6 

 88.9 

 106.0 



117.0 



Square 

 feet. 

 400.0 

 609.5 



574.2 

 833.3 

 761.6 



1,458.6 



Degree. 

 3.9 

 2.6 



2.6 

 2.8 

 3.5 



2.4 



3.1 



3.4 



2.8 

 3.1 

 3.3 



3.5 



7.1 

 15.3 



19.8 

 52.6 

 107.6 



175.5 



1.9 

 3.G 



.62 

 13.20 

 33.50 



59.40 



27.1 

 23.6 



3.1 

 25.1 

 31.1 



33.8 



1 26. 6 



• 30.8 



96.7 

 90.1 







From the viewpoint of the natural increase in heartwood due to 

 larger size, etc., coincident with age, it is presumed that the amount 

 of decay would increase proportionately. The figures obtained in 

 the case of the southwestern-slope type show this to be not only true 

 in this respect, but the proportion of the volume of decay to the 

 total volume of the tree is also much higher. In the river-bottom 

 site (Table III) the average volume of rot increases from 1.9 cubic 

 feet in the 41 to 100 year age class to 3.6 cubic feet in the 101 to 160 

 year age class. In the southwestern-slope type (Table III) a better 

 comparison between age classes can be made. Here a definite 

 increase in rot volume from the 41 to 100 year age class to the 201 

 year and older age class is evident. Table II also shows an irregular 

 increase in the average annual increase in rot volume between age 

 classes, though the general trend of the figures in Table II shows a 

 gradual increase from the younger to the older trees up to the age 

 class 81 to 90 years, after which a gradual decline is noted. This 

 fact might possibly reflect the rate of growth of the tree and therefore 

 of the heartwood and indicate a dropping off in rot activity simul- 

 taneously with a slowing up of the annual growth. 



RELATION OF DECAY TO VIGOR, CROWN RATING, SIZE, AND VOLUME. 



Decay in western hemlock is the main factor of depreciation outside 

 of fire. No other destructive agency operates upon this tree to cause 

 so much waste and none is so diificult to control. The preceding 

 data have shown how the tree, especially when growing in river- 

 bottom sites, is subject to attack by this fungus at an early age, and 

 for the youngest age classes the river-bottom type shows a greater 

 average volume of rot than the southwestern-slope type. In the 

 data secured from lumbermen of the Northwest it is found that a 



