24 



resistant scales of lodgepole cones are efficient protection to the seeds 

 from fires which are hot enough to kill the trees. In slashings and on 

 standing trees the cones are opened by the heat from forest fires, and 

 the seed thus released restocks the burn with even-aged lodgepole j)ine 

 reproduction, often of great density. Douglas fir cones, on the con- 

 trary, are thin-scaled and inflammable. Its mature trees, however, 

 resist fire better, and consequently fir seed trees may be the only sur- 

 vivors when the thin-barked, shallow-rooted lodgepole is destroyed. 

 Under certain conditions, such as immaturity or scarcity of lodgepole 

 cones at the time of the fire, this may result in the predominance of 

 fir in the ensuing stand, but ordinarily lodgepole monopolizes the 

 ground until the maturing stand admits enough light to permit a 

 Douglas fir second growth. 



The two forms differ also in that reproduction of the Rock}^ Moun- 

 tain form is often found growing under the shade of the mature 

 forest, while that of the coast form is practically restricted to clear- 

 ings or to spaces imder large openings in the crown cover. This is 

 due partly to the more open nature of mature forests in the Rocky 

 Mountains and partly to the less humous condition of the forest floor 

 there. 



The coast form of Douglas fir is handicapped in competition with 

 western hemlock, arborvitse, and Sitka spruce by its relatively low 

 reproductive caj)acity on humous soil. In coast Douglas fir stands 

 which contain a mixture of these species the destruction of the mature 

 stand by insects, logging, or disease results almost inevitably in the 

 absence of Douglas fir from the second grov\'th, unless the mineral 

 soil is exposed b}' fire or in lumbering. In very light thinnings of 

 dense mixed stands, even ground burning is apt to prove ineffectual 

 in reestablishing Douglas fir, since most of its associates, especially 

 noble and lowland firs, germinate plentifully in the mineral soil, 

 while all except noble fir outclass Douglas fir in ability to thrive in 

 the shade of the remaining trees. 



In the Eocky Mountains both Engelmann spruce and alpine fir 

 will germinate and grow in mineral soil, and are better able than 

 Douglas fir to grow in pure humus. Douglas fir reproduction is 

 further handicapped in competition with these species by its com- 

 parative inability to endure shade, and when even-aged mixtures of 

 spruce, alpine fir, and Douglas fir come in after burns the latter 

 species rarely appears after the first generation. 



Underbrush often grows sufficiently dense to exclude Douglas fir 

 reproduction from situations in which it would otherwise flourish. 

 This is especially the case in western Washington and Oregon, where 

 salal and similar bushy growths sometimes cover the ground densely, 



[Cir. 150] 



