A6 



protalDly cause more damage to the forests of California 

 during certain seasons than the average annual losses 

 occurring from fires. It has "been determined by the For- 

 est Service that fires result in a concentration of "bark- 

 beetles on areas that have been burned. Healthy trees 

 often resist attacks by the beetles by causing an ex- 

 cess of sap flow. Those which have been slightly ah- 

 jured, however, seem to be preferred by the beetles, as 

 entrance is effected without trouble. Thus, in I9l6, a 

 fire occurred on the Pluijas Hational J'oreet in a pole 

 stand of yellow pine, scorching the crowns, yet not kill- 

 ing the trees. In September 1917. S. B.. Show tallied 

 sample plots on the burned and similar adjacent unburned 

 areas. On the burned area he found that of 37 trees 

 untouched by fire, three had been attacked but had re;- 

 sisted entrance by excessive sap flow; of 31 scorched 

 trees within 50 feet of the others, 13 were attacked 

 and the beetles had gained an entrance. On plots in 

 the unburned timber 200 yards away, l84 poles examined 

 had no pitch-tubes showing the entrance of bark -beetles. 



Studies made by J. E. Patterson on three xxburned 

 areas in RoguTS River County, Oregon, in pine timber, 

 also prove that bark -beetles attack en masse injured 

 trees. On these areas only .7^ of the volume of the 

 stand was killed, 6.5^ severely injured, 27.8^ slightly 

 injured, while 6^% was unharmed. A comparison of the 

 losses due to beetles before and after the fire indic- 

 ated that the increase in destruction on the burned 

 area was 1.177 %, while that immediately outside of the 



