THE TAIGA AND ITS FAUNA 37 
the rigour of the winter climate. The thick branches 
may shelter the ground from snow, the covering of 
dead leaves may protect it from frost; hollow trees 
and dense bushes offer protection to many small 
animals. In short, while the forest does not offer the 
rich pasturage of the steppe in summer, it offers greater 
advantages in winter, and especially greater reserves 
of food. 
One result of this is that on the whole the habit of 
migration is less marked in the animals of the temperate 
forest than in steppe ones. It does occur, but, on the 
other hand, both tundra and steppe animals may seek 
the forest in winter, and the greater uniformity of con- 
ditions in the forest prevents migration occurring on 
the same scale as in steppe and tundra, where areas 
of abundance even in the summer season alternate 
with others where famine reigns. sea Nf a 
As a consequence of the fact that the forest off 
a refuge to animals from other areas, we find that its 
denizens may be divided into two groups. We have 
forms like the squirrel, the dormouse, the lynx, the 
woodpecker, the tree-creeper, the tree-frog, and so 
forth, which are structurally adapted for forest life, 
and are not at home elsewhere, and we also find animals, 
like some kinds of deer and wolf and fox, which show 
no very special adaptations to forest life, but which 
visit the forest for shelter or for food. 
We have already noted that the northern limit of 
the forest is determined by adequate summer warmth. 
Its southern limit depends upon much more complicated 
factors, especially upon the rainfall, and the absence of 
drying winds in winter, when the coldness of the soil 
prevents absorption. A small rainfall, limited to the 
summer months, favours grass rather than trees, and 
