22 The New York State College of Forestry 
the roots of Chamaecdaphne in the sand. Indeed, no case has 
been found anywhere in the bog where the roots of the present 
bog vegetation penetrate the underlying sand. The surface 
becomes much more uneven and more loose and spongy than 
in the sedge zone and although mounds by expansion become 
confluent, there still remains an endless succession of mounds 
and intervening depressions so that walking across this part 
of the marsh becomes a difficult and exhausting task compara- 
ble to floundering through 2 succession of snow drifts. Figure 
11 shows this condition in an interesting way, where deer 
in crossing the marsh have tramped a trench like trail in the 
spongy surface. Figure 13 shows the stump of a burned spruce 
left partly exposed in a zone of rapid growth in thickness of 
the sphagnum-shrub blanket and the underlying fibrous peat. 
The Bog Shrub Species. ‘The shrub species which play a 
role in this invasion of the sphagnum-sedge association are 
chiefly heaths though Spiraea latifolia is of frequent occur- 
rence in the pioneer stages, especially when burning has been 
a factor in delaying shrub invasion. Of the heath shrubs, 
Chamaedaphne calyculata is the most abundant and aggressive. 
Ledum groenlandicum plays a vigorous role especially at a 
later stage when the conifer invasion begins. Vaccinium 
angustifolium, Kalmia angustifolia, end polifolia and even 
Andromeda polifolia are frequent and often prominent, though 
on the whole of rather secondary importance. Of the non- 
heath shrubs, witherod (Viburnum cassinoides) and mountain 
holly (licioides mucronata) are important species notably in 
the older sphagnum-shrub association. They seem to reach 
their greatest abundance and highest stature even after condi- 
tions have favored the invasion by conifer species. 
The expression dwarf heath-shrub association is applicable 
here for in the pure sphagnum-shrub asso¢iation all of the 
shrub growth (both ericaceous and non-ericaceous) is of 
dwarfed stature. Cassandra and Labrador tea persist in the 
conifer association and here are of habitually taller stature 
than in the dwarf heath shrub association. 
