COVER TYPE CLASSIFICATION 



The following descriptions of cover 'types 

 closely follow those of Lutz (1956), but the rela- 

 tion between the cover type and actual fire be- 

 havior within the type is derived primarily from 

 Robinson. 



EARLY STAGES IN FOREST SUCCESSION 



Paper birch {Betula papyrifera). — This 

 species generally forms even-aged stands. With- 

 in 80 years white spruce often becomes promi- 

 nent as an understory component. By 120 years 

 the spruce begins to dominate the stand. Barring 

 major disturbances, the stand eventually be- 

 comes a white spruce-paper birch forest. Fire 

 tends to pe'petuate the birch but reduce the 

 spruce. Birch is typically found over millions of 

 acres as codominant with spruce. The birch tends 

 to open up and have fairly heavy ground cover. 

 Birch stands seldom sustain fire unless some 

 spruce is in mixture with it. Once started, how- 

 ever, fires burn readily in stands containing birch 

 because of the oily, highly flammable bark, 

 which permits flames to race up the trees into 

 the crowns and send sparks and chunks of 

 bark ahead. 



USFS 



Figure 30. — Lichens promote crowning. 



Quaking aspen {Populus tremuloides). — 

 The history of an aspen stand is very similar to 

 that of paper birch. On excessively dry south 

 and west slopes, aspen may persist indefinitely. 



Aspen is relatively short lived, living from 80 to 

 100 years,- it serves primarily as a nurse crop 

 for white spruce. Aspen is seldom found in any 

 extensive areas as codominant with spruce. It 

 tends to have a shallow, clean ground cover, 

 and prunes itself quite rapidly. For this reason, 

 aspen stands are typically more fire resistant 

 than other types. 



USFS 



Figure 31. — Horizontal continuity of fuel. 



USFS 



Figure 32. — Vertical continuity of fuel. 



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