32 



problem connected with this forest is to prevent more tolerant species, 

 especially western hemlock, from growing up under Douglas fir and 

 gradually securing permanent possession of the ground. The best 

 solution to this problem will usually be to cut clean and burn over 

 the surface. Douglas fir reproduction will thus find abundant light 

 and a mineral soil, and by its prolific seed production and the density 

 and rapid growth of the young stand may reasonably be expected to 

 exclude from the stand even the more tolerant reproduction of hem- 

 lock, arborvitse, or spruce. Since at maturity such even-aged stands 

 of Douglas fir are apt to run quite uniformly above the minimum 

 merchantable diameter limit, clean cutting is justified from a com- 

 mercial standpoint. The mineral soil exposed by ground burning 

 also affords an excellent seed bed for noble fir and western white 

 pine, desirable associates of Douglas fir, and in some localities this 

 encouragement may be advantageous. 



Clean cutting to the lowest merchantable diameter limit should, 

 then, be the general plan for the greater part of this type of forest, 

 except on steep slopes with shallow soil. On. steep slopes and ridges 

 the forest should usually be held intact, since the trees are apt to be 

 shorter and knotty and, therefore, of inferior commercial value, but 

 they are of the greatest value as sources of seed for restocking the 

 adjoining cuttings. Great care must be exercised to leave only firmly 

 rooted specimens for seed trees after dense stands are logged, since 

 isolated trees in such situations are particularly subject to windfall. 

 In some situations they should be left in groups, to afford each other 

 mutual protection during the period necessary for establishing re- 

 production. Trees growing in the more open parts of the stand are 

 usually shorter, knottier, and more wind-firm than those in the denser 

 portions, and are therefore more desirable for seed trees than for logs. 



^"\Tiere the forest is not pure Douglas fir, but contains a consider- 

 able proportion of hemlock, cedar, spruce, or balsam, the cuttings 

 should aim, in localities suitable for Douglas fir, to remoA^e all mer- 

 chantable timber of each species except enough Douglas fir seed trees 

 to insure an abundant reproduction. The surface should then be 

 burned over to remove the forest litter and humus, and to expose the 

 mineral soil. In this type of forest, heavy cuttings are necessary for 

 the successful reproduction of Douglas fir on account of the great 

 density of the stands and the heavy accumulations of forest litter 

 which are characteristic of them. Except in very heavy thinnings, 

 amounting practically to clean cutting, surface burning can not be 

 practiced without great danger to the remaining trees, but when the 

 mature stand is removed the surface may, with due precautions, be 



[Cir. 150] 



