14 University of Michigan 



Erethizon epixanthum myops. Alaska porcupine. 

 Citellus osgoodi. Yukon ground squirrel (Osgood). 

 Castor canadensis canadensis. Canada beaver. 

 Lepus americanus macfarlani. Macfarlane snowshoe hare. 

 Alces gigas. Alaska moose. 



On the mud bars along the larger rivers and at the outer edge 

 of the grassy areas about lakes a growth of willows, Salix, is likely 

 to spring up. Alders, Alnus, occur sometimes mixed with the 

 willows and rarely form pure stands, seeming to represent mostly 

 a stage following the willows. Willows and alders rarely form 

 isolated thickets in patches of niggerheads. The ground under 

 the growth of willows and alders is often bare, but may in wet 

 situations on mud bars be covered by horsetails, or in the drier 

 areas about lakes by grasses and other herbs. An older growth 

 of willows may attain a treelike form, and rarely alders also attain 

 considerable size; but old growths of either willow or alder are 

 rare, for these formations are rapidly replaced by poplars and by 

 the more permanent types of forest. 



Thickets of willows and of alders, the two sometimes mixed 

 together, occur along the smaller creeks up to timber-line, there 

 connecting with the timber-line willow-alder habitat, which is here 

 considered as distinct. The distinction between the willow and 

 alder habitats of the lowlands and highlands is, however, not sharp, 

 and subsequent observations may show that the two should be 

 combined. 



Poplar habitat and association: 



Colaptcs auratus borcalis. Boreal flicker. Summer (Osgood). 

 Vnlpes alascensis alascensis. Alaska red fox. 

 Microtus xanthognathus . Yellow-nosed vole (Osgood). 



Forests of poplar, Populus candicans, occur in the valley of the 

 Yukon, where they are best developed on islands. Fringes of 

 poplars between the willow-alder thickets and white spruce-paper 

 birch forest may often be seen. Along the Kuskokwim the 

 poplar seems to be much less abundant. 



