FORESTRY BRANCH BULLETIN NO. 33 



decade was calculated and the per cent growth during each decade calculated by the 

 formula 



+v 



x 200 



The diameter growth was also plotted on cross-section paper. 



FIEE. 



A splendid opportunity is given in the Rocky Mountains for studying the 

 influence of fire, since conclusions can be drawn from recently burned areas, show- 

 ing exactly the condition of the seed-bed; from young second-growth, showing the 

 material from which the final stand will be formed ; and from mature stands, which 

 started to grow after some ancient fire, and which show the final result of conditions 

 noted in the earlier periods. 



The forest fires of this region are notable for their intensity and the complete- 

 ness of the destruction wrought by them. Some of the reasons for this are connected 

 with the mountainous topography. The steep slopes aid the flames in gathering 



Plate 7 Effect of Fire in Dense Stand. 



Photo G. Cromie. 



headway and the narrow valleys with their high sides create a tremendous draft. 

 The continuous and dense coniferous stands are also responsible. Spruce has the 

 lowest crown and the flames easily rise to the top, but pine usually grows with a 

 more uniform crown-cover, with more trees to the acre and on drier sites and there- 

 fore is more susceptible to crown fires. Both species are shallow-rooted and thin- 

 barked, and hence easily killed. Spruce roots are so near the surface that ground 

 fires, which do not directly kill or weaken the trees, burn off enough rootlets to cause 

 them to be wind-felled. In general, burned tracts have very few trees left living, 

 has an important effect on the character of the succeeding stand. 



