422 JOURNAL OF FORESTRY 



That the rat is a factor in the number of trees in the various 

 height classes in a stand can not be doubted. Table 4, which gives 

 the result of several measurements of trees growing either in the open 

 or among sage brush and of the trees on the sample plot, shows this 

 very plainly. 



Table 4. — Number of Trees by Height Classes in the Open and in Brush 



Besides the. actual damage done to the trees, there is a secondary 

 damage which might at any time become more imiportant than the 

 rats, namely, the bark beetle, Dendroctonus valens. On the plot in 

 which most of the work described here was done, 3 of the 2(5 dead 

 trees showed that this insect had been present before the death of the 

 tree; 12, or 57 per cent, of the trees seriously injured were affected; 

 and 6, or 35 per cent, of the trees slightly injured had pitch tubes. 

 Altogether a total of 21 trees, or 20 per cent, of the entire stand had 

 been hosts for the beetle. Thus, on a large area of young trees, 

 whether natural or artificial, if the rats are not kept within bounds 

 the trees may be wounded and the beetles therefore attracted, with the 

 resulting danger of an infestation which might sweep off the entire 

 stand. 



The damage done by the rat has an important bearing on reforesta- 

 tion work because of the difficulty of poisoning the rodents which are 

 so abundant in the chaparral, and because of the slow growth of the 

 trees. Stem analysis of nearly 100 trees has shown that at the height 

 of 7 feet there is a difference of 8 years between trees grow- 



