12 



THE WESTERN HEMLOCK. 



come up beneath a heavy .stand of mature timber. Hemlock and 

 Cedar thrive under cover and, where climate and soil are favorable, 

 occur in stands containing" trees differing - widely in age, since } T oung 

 trees are continually growing up to replace those which die and are 

 blown down. In a forest of Red Fir, however, the trees are practi- 

 cally of the same age and no reproduction takes place until a large 

 proportion of them are removed and light is freely admitted to the 

 ground. This is usually accomplished by fire. 



Where, as is frequent, the forest consists of an upper story of large 

 Fir and a lower story of Hemlock of varying age, it often occurs that 



240 



20 



40 



60 



80 



100 120 140 160 180 200 220 240 260 280 300 

 AGE-YEARS 



Fig. 1.— Diagram showing height growth of mature Red Fir and of Hemlock growing beneath it, 



calculated on a basis of age. 



as the Fir dies the Hemlock gradually takes its place. Where Fir is 

 killed out by conk or ground- rot, the process is often rapid; and exami- 

 nation shows that the small areas stocked with a pure growth of young 

 Hemlock, so often seen in the midst of a Fir forest, were often caused 

 by this means. It is probable that disease in the old Red Fir forests 

 is largely responsible for the present distribution of Hemlock in 

 Washing-ton and Oregon. 



GROWTH UNDER COVER. 



No tree grows as rapidly in the shade as it does in the light, and 

 Hemlock which has come in under Fir shows a close and often very 



