CONIFERS OF THE ROCKY MOUNTAIN REGION. 15 



in moisture. In dryish poor soils, it seeks chiefly cooler, northern 

 aspects. Lack of soil and moisture produces stunted growth, as do 

 also high elevations, even when abundant moisture and good soils 

 are present. 



Western hemlock is usually a subordinate species in association 

 with other trees; but sometimes forms the dominant growth, espe- 

 cially in its far northwestern range, where occasional pure stands also 

 occur. Generally it is scattered in patches, groups, or singly through 

 the forest. From the Pacific coast to the Rocky Mountains its com- 

 mon associates are Alaska cypress (Pacific region) , Douglas fir, west- 

 ern red cedar, lowland white fir, silver fir (Pacific region), western 

 white pine, Engelmann spruce, lodgepole pine, and western yew. It 

 is occasionally associated with mountain hemlock. 



Tsuga heterophylla is extremely tolerant of shade throughout its 

 life, especially during the seedling stages. In later life, however, ver- 

 tical light is necessary for the best growth. Prolonged suppression 

 in dense shade greatly checks growth; but when overhead light is 

 admitted, the trees recover remarkably well from long suppression 

 and soon increase their rate of growth. Western hemlock maintains 

 dense stands when growing alone, subordinate to others, or as the 

 dominating tree with equally tolerant or slow-growing species. The 

 ability of this tree to grow throughout its life in the densest shade 

 explains the often almost pure stands that have followed the removal 

 of the older forest in which hemlock was widely but only sparingly 

 represented. The hemlock seedlings had covered the shaded ground 

 in this older forest, and later excluded other less tolerant species try- 

 ing to come in after the old trees were removed. 



Western hemlock is a very prolific seeder, reproducing itself freely 

 everywhere under favorable conditions. Trees 25 to 30 years old 

 may begin to bear seed. Some seed is produced every year, but heavy 

 seed years occur at irregular intervals of from two to three years. The 

 seed has only a moderate rate of germination and fairly persistent 

 vitality. Germination is excellent and growth of seedlings good on 

 wet moss, humus, litter, decaying wood, muck, and mineral soils, 

 the latter being less favorable than a seed bed of moist vegetable 

 matter. In the dense, moist forests in which this tree grows best, 

 its numerous seedlings are a familiar sight on moss-covered stumps 

 and logs— often lodged high in the air — and even in the moss on 

 living trunks. Not infrequently seedlings extend their roots through 

 or over these decaying stumps or logs into the soil and become firmly 

 rooted; many others, unable to do this, die. 22 Reproduction occurs 

 abundantly under the dense shade of mature stands and also in the 



22 Mr. F. H. Conant, of Auburn, Wash., an old timber cruiser, says in a letter to the writer under date 

 Of Feb. 12, 1909, that during logging operations in (sec. 15, T. 21 N., R. 8 E.) west Washington a 240-year- 

 old western hemlock was cut that had grown upon the prostrate trunk of an old Douglas fir. 



