12 University of Michigan 



Niggerhead habitat and association: 



Lagopus lagopus albus. Willow ptarmigan. Resident. 



Sorex personalus arclicus. Arctic shrew. 



Sorex tundrensis. Tundra shrew. 



Microsorex eximius. Alaska microsorex. 



Muslda arctica arctka. Arctic weasel. 



Mustela vison in gens. Alaska mink. 



Lenimus yukonensis. Yukon lemming. 



Evotomys dawsoni dawsoni. Dawson red-backed vole. 



Microtus pennsylvankus drummondi. Drummond vole. 



Microtus operariiis endwciis. Interior vole. 



Alces gigas. Alaska moose. 



Extensive areas of niggerheads occur in parts of the valleys 

 where drainage is poor. These niggerheads are tussocks of tough 

 grass, which elongate each year until the head may be several feet 

 above the ground. The heads usually grow close together, there 

 being usually a free space of six to twelve inches between the 

 pedestals. The ground is bare and moist. Willows, alders, 

 blueberries, and other shrubs when present grow thinly; or in 

 places the willows or the blueberries increase sufficiently to domi- 

 nate, giving rise to a different type of habitat. 



Niggerheads also occur on nearly level slopes up to and above 

 timber-line. In such places a growth of blueberries and dwarf 

 birch, with sphagnum growing between the niggerheads, is com- 

 monly dominant and areas of pure niggerheads are infrequent. 



On the somewhat better-drained ground around the belt of 

 sedges surrounding a lake, grasses, mostly in tussocks of the nigger- 

 head type, are common and may form a distinct belt. Thickets 

 of willows and alders frequently invade this belt from the edge of 

 the forest, and isolated thickets of these shrubs may appear in the 

 midst of a large area of niggerheads. 



In time the niggerheads of poorly drained situations seem to be 

 invaded by sphagnum, which ultimately fills the interstices between 

 the heads, and, if below timber-line, black spruces appear, and 

 finally the area becomes a black spruce forest. 



