Occasional Papers of the Museum of Zoology 1 7 



forest are the willows, Salix, poplar, Fopulus candicans, a red birch, 

 perhaps a color phase of Betula alaskana, and black spruce, Picea 

 mariana. A considerable amount of underbrush chiefly of alder, 

 Alnus, occurs. If the shade is not too heavy there are also 

 grasses and a few shrubs such as the high-bush cranberry, Viburnum 

 pauciflorum, trailing juniper, Juniperus sibirica, and bearberry, 

 Arctostaphylos uva-ursi. 



The altitudinal range of this type of forest is usually not high, 

 though on the warm and well-drained southern slopes of Mount 

 Sischu a burned forest of white spruce and birch was found to have 

 formerly extended up to timber-line. 



Nearly pure forests of Alaska paper birch occur on some warm 

 slopes. The trees in these forests are quite uniform in height and 

 apparently in age, and vary from six to twelve inches in diameter, 

 with a height of about sixty feet. Such forests are particularly 

 common on the slopes near Lake Minchumina, where they have 

 apparently developed following a fire. The ground under the 

 birches is usually covered by a heavy growth of bearberry. In 

 this type of forest young white spruces often occur, and the whole 

 forest is seemingly a younger stage in the development of a white 

 spruce forest. 



A few groves of nearly pure white spruces occur along the 

 stream margins in the broader valleys. These groves are usually 

 small in extent, probably because the streams, undercutting their 

 banks in their meanders across the valleys, do not give time to 

 develop any considerable extent of white spruce forest to full 

 maturity. The trees even in the larger groves seldom have a 

 greater diameter than two feet. The forest floor under the white 

 spruces is either nearly bare of vegetation and covered by spruce 

 needles, or in open forest a growth of grass may be present. 



The occurrence of a pure forest of either paper birch or white 

 spruce is rare, the common condition being a mixed forest with 

 these two species represented in varying proportions. 



