22 Mammals of Eastern Asia 
kinds of plants that grow well or even best under special con- 
ditions, such as aridity, swamp, soil acidity or alkalinity, intense 
light or shade. This interplay of very different responses in 
many sorts of plants to multitudes of stimuli results in the pro- 
duction of the local patches of forest, pasture, and bog that in 
turn provide the vegetational element in an animal's environ- 
ment. 
Even these environmental factors — climate, land and vegeta- 
tion — are not all. There are many others of importance, such as 
the abundance of predators, the state of the food supply, and 
the incidence of parasitic and other diseases, but those just dis- 
cussed are three of the most important elements that affect the 
lives of most free-living animals. The interaction on the indi- 
viduals of a species of all its environmental elements determines 
whether it can continue to live where it is, whether it can in- 
crease in numbers or, on the contrary, is fated to become extinct. 
It is neither possible nor suitable in this book to try to give 
descriptions of the very numerous and complex local environ- 
ments present through the coastal areas of eastern Asia. On the 
other hand, a series of brief vignettes of larger divisions, known 
as "faunal areas," may help readers to visualize some of the 
local conditions among which Asiatic mammals live. 
The Tundra, generally frozen throughout the year, with the 
exception of a few inches of the surface soil in summer, is the 
treeless, rather arid circumpolar belt lying between the Northern 
Forest belt and the Arctic Ocean. Most of the plants that grow 
there are either dwarf perennials or annuals of quick growth. 
The equivalent of tundra develops on the tops of the highest 
mountains just below snow-line. The mammals present include 
Shrews, Bears, Wolves, Arctic Foxes, Weasels, Pikas, Arctic 
Hares, Ground Squirrels, Woodchucks, Red-backed Mice, 
Beaver, Lemmings and Lemming Mice, Caribou, Moose, Sheep, 
Reindeer. 
The Northern Forest Belt is also circumpolar. In Siberia 
