﻿1916] SHAW— THE SELKIRKS 487 



dominate the vegetation in considerable areas; but it never 

 entirely excludes the spruce, the mountain pine, and the Douglas fir. 

 Within the area it is one of the most prominent trees of the burns, 

 seeming in this respect like the lodgepole pine. 



Thuja plicata is, at least in some respects, the monarch of plants 

 in the Selkirks. Occurring sparsely in the Rockies and upper 

 Columbia Valley, it finds its proper home in the deep moist valleys 

 of the western arm of the Columbia. Here it not seldom reaches 

 a diameter of 3 m. The trunk tapers rapidly, however, and is 

 seldom over 50 m. high. Another fact which detracts from its 

 timber value is that the trunks are usually decay e d within, a large 

 and sound tree being almost unknown. 



Pseudotsuga mucronata shows ability to endure and to respond 

 to a wide variety of conditions. As is well known, it reaches a 

 huge development in the Puget Sound country, forming perhaps the 

 most magnificent forests on the globe. Nevertheless, it endures 

 conditions of dryness better than most of the other conifers. It 

 extends south to Colorado and beyond, and in Canada, as one 

 passes from the treeless plain to the foothills, it is one of the first 

 trees to appear. In the region we are studying it is nowhere 

 abundant, yet it occurs throughout. It grows largest on the west- 

 ern slopes of the Selkirks, making there a diameter of 2 m. and a 

 height of 65 m. or more. 



Pinus monticola, a large white pine, is scattered through the 

 area, nowhere very abundant, but becoming a valuable timber 

 tree in the hemlock district. 



Populus balsa mi J era occurs constantly along the river, some- 

 times forming forests several hundred meters wide. It reaches a 

 diameter of 1-2 . 5 m. and a height of 30-45 m. 



Pinus Murray ana, the lodgepole pine, is remarkable both for 

 its limited distribution and for the part it plays in reforestation. 

 In all the region where it occurs it is the first tree to spring up 

 after a fire. In the Rockies particularly, the burn forest is often 

 almost purely lodgepole pine. Its range is sharply confined to the 

 Rockies and the drier portion of the Selkirks, ceasing rather 

 abruptly where the hemlock begins. The cause of the peculiar 

 distribution is not wholly clear. Possibly it cannot survive in 



