21 



displace Douglas fir. The Rocky Mountain Douglas fir, also, gives 

 way to Engelmann spruce and alpine fir when it comes into conflict 

 with these species for the best soils. Both forms of Douglas fir, 

 when forced by other species from preferred situations, maintain 

 themselves by their better ability to grow on poor soil until some 

 accident to the monopolizing stand allows them to return. 



TOLERANCE. 



One of the most important considerations in the management of 

 Douglas fir is its demand for light and its relation in this respect 

 to associated species. The coast form is less tolerant than all its 

 important associates except yellow pine, western larch, and noble fir. 

 It maintains its supremacy in the forest of this region through its 

 adaptabilit}^ to var^dng conditions of soil and moisture and through 

 its extraordinary aggressiveness in seeding doAvn burns and other 

 openings in the forest. In California and southern Oregon it is 

 relatively tolerant as compared with the light-demanding species 

 with which it associates; it is more tolerant than yellow and sugar 

 pines and only slightly less so than incense cedar and white fir. 



The mountain form is considerably less tolerant than its frequent 

 associates, Engelmann spruce and alpine fir, and slightly less so 

 than white fir, but will endure more shade than western larch, west- 

 ern yellow pine, lodgepole pine, and the pinions, junipers, and aspen. 

 In the relatively light shade of mature lodgepole stands, Douglas fir 

 reproduction makes better growth than that of the pine itself, and 

 ma}^, if suited by soil and moisture, outnumber the pine in the suc- 

 ceeding forest. Young lodgepole stands and the forests of the Engel- 

 mann spruce type, however, are too dense for successful Douglas 

 fir reproduction. 



Under heavy shade Douglas fir seedlings soon die out. With mod- 

 erate overhead shade they maintain a slow, spindling growth for a 

 number of years before they succumb. If released from shade after 

 a few years' suppression they recover and make fair growth, but do 

 not possess nearly so much vigor as trees grown from youth with 

 plenty of overhead light. In ability to exist under shade and to 

 recover from suppression, Douglas fir is outclassed in the Hocky 

 Mountains by Engelmann spruce and alpine fir. In the coast region 

 nearly all its associates show greater capacity in this respect. 



Though it demands for its best growth an abundance of light, 

 Douglas fir produces the tallest, straightest stems when well shaded 

 from the side. Its branches are rather persistent, and remain on the 

 stems long after the foliage has died from lack of light. If, however, 

 these branches succumb to shading in early youth, as is the case when 

 Douglas fir grows up in dense stands, they are broken from the trunk 



[Cii\ 150] 



