22 



at "a short distance below the live crown and leave the mature sterns 

 clear for a long distance. 



"When it is given an equal chance with other species in the competi- 

 tion for light, Douglas fir grows rapidly, and on account of its large 

 size usually assumes a dominant position in the stand. It makes its 

 best growth under such conditions, since its relatively wide and deep 

 root system allows it to compete successfully with the more shallow- 

 rooted species among its associates. If the latter are tolerant species, 

 however, such mixtures usuallj^ constitute only temporary types for 

 Douglas fir, since, other conditions being equal, these more tolerant 

 trees will be able to shade out the Douglas fir reproduction and 

 exclude it from the ensuing stand. 



KEPRODUCTIOX. 



The reproductive capacity of the several species is the most vital 

 factor in determining the composition of a forest. Few western 

 conifers outrank Douglas fir in abundance and vigor of reproduction. 

 It begins to produce cones early, and continues to bear seed almost 

 every year up to an advanced age. Under favorable soil and climatic 

 conditions, a large proportion of the seed will genPxinate and produce 

 seedlings. In some jears seed production is much more abundant 

 than in others. Just how often these heavy crops of seed are borne 

 is not known with certaint}^, but it is probable that they come at 

 fairly regular intervals of from three to five years, varying with the 

 region and situation. 'Not infrequently many of the cones are 

 barren. 



In the coast region Douglas fir only 12 years old has been found 

 bearing cones. In the Rocky Mountains the minimum cone-bearing 

 age is recorded as 20 years. As a rule, however, the period of abun- 

 dant cone production rarely begins, even in open-grown trees, before 

 the fortieth or fiftieth year, and when the trees grow in partial shade 

 it is retarded until a much later date. A full supply of light is essen- 

 tial for good seed production, and hence trees in dense stands do not 

 bear so abundantly as open-grown trees, since only their top branches 

 receive the requisite amount of light. Although Douglas fir con- 

 tinues to produce cones late in life, the abundance of production 

 ultimately falls oif, and extremely old trees bear very lightly. 



The cones, which are borne on all parts of the crown and are not 

 confined to the top, as in the true firs, may remain tightlj"' closed for 

 as much as three weeks after they become fully ripe. ^Vhen they do 

 open, the seeds, which are provided with large wings, are scattered 

 by the wind and may be carried to a considerable distance from the 

 seed tree, depending on the strength of the wind, the density of the 

 forest, and the topography. The approximate radius of reproduction 



[Cir. 150] 



