18 
250 miles beyond the edge of the forest. Marr (1948), as a result 
of field observations in the Richmond Gulf area on the east coast 
of Hudson Bay , concluded that “Areas unsuitable for trees because 
of absence of soil are occupied by tundra. Trees are invading 
tundra areas as soil develops.” Hustich (1953) notes that there 
has been a fairly well-marked amelioration of the climate of the 
forest-tundra region of northern Eurasia during the last few 
decades but is doubtful that the same can be said for Eastern 
Canada. However, since the mean annual temperature of the 
Richmond Gulf area is only two or three degrees higher than that 
at Churchill (Jenness, 1949, Map 2; Thomas, 1953, Chart 1-9) 
and the mean July daily temperature at Churchill is indicated as 
somewhat higher than at Richmond Gulf (Thomas, 1953, Chart 
1-5), it is probable that essentially the same factors are in oper- 
ation at both localities. Ritchie (1957) is of the opinion that there 
is clear evidence in an area east of the Churchill River estuary 
that “the white spruce forest is invading the younger, shrub- 
dominated flats, and that it is ultimately replaced by a black 
spruce community on large peat mounds.” 
Variations in soil temperature may help to explain local 
tree distribution. Beckel (1954) found that greater extremes in 
temperature occur at or near the surface of soil in higher, drier 
areas than in lower, wetter areas. The accumulation of snow by 
drifting from higher to lower areas also serves to insulate the 
lower areas against extreme lowering of soil temperatures. Beckel 
(1957) found that in areas where there was a great accumulation 
of snow during the early part of the winter or where the upper 
limit of permafrost occurred at great depths, as in wet, sandy 
soils, the lower levels of the active soil layer rarely reached 
freezing temperatures. 
Another way in which low temperature affects vegetation 
is the disturbing action of frost on the active ground layer. 
“Drunken forest” phenomena are particularly noticeable along 
the banks of the Hayes, Nelson, and Churchill rivers where 
thawing of the marine clays has resulted in mass movement of 
the substratum. Their occurrence on level areas is believed to 
result from the expansion of frost mounds under them in much 
