25 



preventing the development of even the shade-enduring trees. The 

 salal has a resinous foliage, however, and in dry seasons surface 

 fires burn readily in it, leaving ideal seed-bed conditions for Douglas 

 fir reproduction. In the southern Rocky Mountain region some kinds 

 of undergrowth afford a much-needed protection from extremes of 

 heat and cold, and seedlings thrive in their light shade. Light sod 

 does not prevent the germination and growth of Douglas fir, though 

 reproduction is slow on grassy areas. In some portions of its Rocky 

 Mountain range it is gradually encroaching on the grass-covered 

 mountain parks, some of which it promises eventually to reclaim. 



The inability of Douglas fir to reproduce in dense shade or on 

 very humous soils is an important factor in determining the manage- 

 ment of the forests in which it grows. In the coast region, where it 

 grows mixed with western hemlock and other tolerant species which 

 germinate on leaf litter, the proportion of fir cut should be reduced 

 to a minimum, while the thinnings of all other species should be 

 heavy enough to admit abundant light. The brush should be piled 

 and burned to expose the mineral soil, and, if it can be done safely, 

 the surface should be burned over for the same purpose. To re- 

 place young stands of inferior species, such as lowland and noble 

 firs and western hemlock, it may be advisable to destroy these sj)ecies 

 by burning, provided Douglas fir seed trees are present and there 

 is a certainty of an abundant seed crop. In the Rocky Mountains, 

 where other species more aggressive in restocking burns are present, 

 the encouragement of Douglas fir by surface burning becomes hazard- 

 ous. The ability of Douglas fir to germinate and grow in light 

 humus and under moderate shade would suggest a thinning without 

 surface burning or with brush piling and burning. Where the dan- 

 gler from windfall does not have to be considered, the heaviness of 

 the thinning should depend on the proportion of Douglas fir seed 

 trees in the stand. 



SUSCEPTIBILITY TO INJURY. 



Generally speaking, Douglas fir is less susceptible to the ordinary 

 enemies of the forest than most of its associates. There are a number 

 of influences, however, which are capable of working great damage to 

 Douglas fir, both in natural and in planted forests. The chief inor- 

 ganic enemies of Douglas fir are fire, wind, and frost. 



Except in youth, Douglas fir is remarkably well able to withstand 

 fire. The thin bark of the young stem, which is thickly set with 

 resin blisters, changes with increasing age to a thick coat of fire- 



[Cir. 150] 



