84 A Study of the Vegetation of 



the young trees can not endure shade. However, openings of 

 greater or lesser extent constantly occur in primeval forests due to 

 the dropping out of old trees, to windfalls or to fires. Since 

 Larix seedlings can do well in openings where the sunlight enters 

 during the middle of the day, the chances for reproduction are 

 always present. The tamarack, because of its thick bark, is dis- 

 tinctly a fire-resistant tree, often remaining unscathed where 

 white pine and white fir are killed. Hence, large tracts of burned 

 areas, where the tamarack was abundant, now appear to form 

 nearly pure Larix communities. However, an examination of the 

 new tree populations, together with comparisons with unburned 

 contiguous areas, reveals the true mixed nature of the original 

 forest. In such places the white fir is especially prominent. 



Abies grandis is not only more tolerant of shade but is also more 

 mesophytic than the larch. I have not infrequently found fir 

 seedlings in shade so dense as to exclude all other trees except 

 the cedar. White fir seedlings can grow in light as low as 0.02 

 to 0.015. Under such conditions, however, growth is poor. While 

 it can develop in open places in rather dry soil, it is more exacting 

 in soil moisture requirements than either Douglas fir or Larix. 



The position of Abies in the normal succession is beautifully 

 illustrated on sheltered slopes of outlying mountain spurs and 

 buttes. Passing from the dry open pine forest one can find all 

 stages from pine-Douglas fir mixture dominated first by the pine, 

 to a pine-fir-tamarack mictium where the tall, spindly, bushy- 

 topped pines, many of which are dead, tell the story of the lost 

 struggle for light. Areas of higher water content on the same 

 slope may show Pseudotsuga-Larix mixtures with the fir losing its 

 dominance and Abies grandis appearing. The next stage is that 

 of a Larix-Abies mictium with the coming in of cedar. Charac- 

 teristic plants of these drier Larix-Abies forests are given in the 

 following lists : 



Ceanothus sanguineus Ribes viscosissiwmm 



Holodiscus discolor Rosa gymnocarpa 



Opulaster pauciflorus Rubus parviflorus 



Pachistima myrsinites Salix scouleriana 



84 



