Four Billion Feet of Beetle-Killed Spruce 



419 



multiplication of beetle populations 

 are windfalls and overmaturity of the 

 spruce stands, since the insects prefer 

 to attack the larger mature trees and 

 produce heavier broods in them. Large 

 bodies of windthrown timber provide 

 highly favorable conditions for the 

 build-up of beetle populations, because 

 green trees that have been blown over 

 have been seriously disturbed in their 

 crown and root functions and can offer 

 little resistance to the attacks of the in- 

 sects. After strong populations have de- 

 veloped, they will attack green stands 

 of spruce regardless of their condition, 

 and heavy losses usually continue until 

 natural control factors again gain the 

 upper hand. 



PREVIOUS OUTBREAKS of the Engel- 

 mann spruce beetle occurred in the 

 Rocky Mountain region, but most of 

 them were so long ago that their exact 

 extent is not known. In 1907, A. D. 

 Hopkins, of the Department of Agri- 

 culture, found evidence on the White 

 River National Forest of an outbreak 

 that occurred 20 to 25 years earlier. He 

 also estimated that severe outbreaks oc- 

 curred on the Pike National Forest 

 about 1855 and on the Lincoln Nation- 

 al Forest in New Mexico about 1890. 

 An outbreak that killed nearly 100 per- 

 cent of the spruce volume swept over 

 the Aquarius Plateau in Utah between 

 1918 and 1928. A localized outbreak 

 was reported in the northwestern part 

 of Yellowstone National Park in 1937. 

 Apparently none of these earlier out- 

 breaks even approached in intensity 

 and total volume of destruction the one 

 that started in Colorado in 1942. 



Circumstances beyond the control of 

 foresters and entomologists caused this 

 spectacular outbreak. Several factors 

 made conditions favorable. In June 

 1939 a severe windstorm swept from 

 the southwestern corner of Colorado, 

 in a northeasterly direction, across the 

 mesa-type plateaus in the State. On 

 thousands of acres many of the shallow- 

 rooted Engelmann spruce blew over. 

 Many of the roots on the down side 

 remained in the soil to keep the trees 



alive for several years or until the 

 beetles made their attack. As a native 

 species, the Engelmann spruce beetle 

 was present in small numbers in deca- 

 dent trees in the forest. Those down 

 trees proved to be a fertile breeding 

 place for them. 



By 1942, this breeding material had 

 been consumed and the beetles had 

 built up great populations. With a pre- 

 viously unknown reproductive force, 

 coupled with an apparent lack of 

 activity of natural control factors, the 

 beetles invaded the standing spruce. 

 By 1943, when the infestation was first 

 discovered, the number of infested 

 trees was so great that control by de- 

 stroying the insects with fire or insec- 

 ticides was economically and physically 

 impossible. The problem then became 

 one of determining the extent and se- 

 verity of the outbreak so as to prevent 

 its spread into other spruce forests, sal- 

 vaging the dead timber, and studying 

 the life history and habits of the beetle 

 as a basis for development of control 

 measures. 



PLANS WERE MADE in 1943 for a sur- 

 vey of the spruce type in Colorado to 

 determine the extent of the outbreaks 

 and their progress, what action should 

 be taken, and whether spread of the in- 

 sect into nonaffected areas could be 

 prevented. 



A person who has not visited the 

 high Rockies in Colorado can hardly 

 realize the difficulties of making a sur- 

 vey and carrying out control measures 

 in the spruce forests. Engelmann spruce 

 grows at elevations of 9,500 to 11,500 

 feet, generally in rugged terrain ex- 

 cept for the forests on plateaus and 

 in places where few roads have been 

 made. Many of the areas can be 

 reached only by a trail, and then often 

 with as much as a full day's travel on 

 pack animals from the end of a road. 

 An attempt was made in 1944 to use 

 an airplane to scout the forests and 

 locate the incipient outbreaks, but the 

 infestations could not be detected from 

 above because of lack of foliage dis- 

 coloration. Nor could incipient out- 



