FOREST PLANTING IN THE INTERMOUNTAIN REGION. 25 



Sites suitable for Douglas fir. — This species has been planted on 

 four general classes of sites: (1) Under aspen of varying densities; 

 (2) comparatively open recent Douglas fir burns; (3) temporary 

 brush lands which are potential Douglas fir sites, from which the 

 original forest cover has been removed either by early fires or by 

 heavy cutting; (4) northern aspects in oak brush (PL VI, figs. 1 

 and 2). The results obtained on all of the experimental plantations 

 are summarized in Table 12. 



Many of the plantations of Douglas fir under aspen in Utah re- 

 sulted unsatisfactorily, owing mainly to the use of small planting 

 stock and to snow-molding. Snow-molding is serious in proportion 

 to the length of time the snow lies on the ground in the spring and 

 it therefore becomes more serious as altitude increases. This is 

 especially true under aspen, which not only tends to retard snow 

 melting to a certain extent, but which also forms a favorable sub- 

 stratum by its leaf fall for the development of the fungi. For this 

 reason, results range all the way from entire failure in two years to 

 62 per cent survival after seven years. The former occurred at an 

 elevation of 8,700 feet, the latter at 7,500 feet elevation. If altitude 

 is correlated with average survival the second year, the indications 

 are that at 7,500 feet elevation the survival would be normally 65 

 per cent, above which it would normally fall 10 per cent for every 

 250 feet increase in elevation. On the Mink Creek watershed in 

 southern Idaho where snow molding has not been serious, a survival 

 of as much as 95 per cent of vigorous trees at the end of the third 

 year was obtained with 3-2 stock. 



Losses on the open Douglas-fir burns were quite heavy, owing 

 mainly to lack of sufficient shade to tide the trees over dry periods. 

 In the oak brush zone survival has been generally poor and growth 

 is below normal. However, a survival of 72 per cent has been se- 

 cured with 3-2 stock at the end of three years on the more favorable 

 northern aspects. This result is especially encouraging because the 

 growth is practically as good as on any of the plantations. Frost 

 injury is likely to be serious at the lower elevations, and for this 

 reason it is desirable at the lower elevations to plant on steep north- 

 ern aspects where spring budding is delayed as much as possible, 

 and yet where cold air does not settle. 



The shade of the oak brush cover and the moisture found on such 

 sites are factors favorable also to summer survival; but in sage- 

 brush the results are very poor, as the sites in the summer are drier 

 than oak brush, while sagebrush is almost always found in flats and 

 hollows subject to severe spring frosts. 



The conclusions regarding the planting of Douglas fir in this region 

 may be summarized as follows : 



1. The aspen type in Utah, southern Idaho, and western Wyoming 

 can be successfully underplanted with either 3-1, 3-2, or 3-0 Douglas 

 fir stock, preferably the first-age class. 3 



3 In order that the emphasis placed upon 3-1 stock may not be misconstrued, it is necessary to recall 

 what has already been said, and shown in Figures 1, 2, and 4, regarding the susceptibility of Douglas fir 

 to frost injury. It was not possible to grow good Douglas fir nursery stock until the frost injury and snow- 

 molding problems had been solved. The available 3-2 stock was in most cases severely injured by at least 

 one severe freeze, making it somewhat inferior to uninjured 3-1 stock. General nursery experience in this 

 region as well as the writers' studies, all point to the superiority of 3-1 stock. 



91913°— 25 4 



