FOREST COMMUNITIES 437 



the tropical forests and lack the low underbrush except in openings or 

 near the borders. They are also deficient in lianas except in the lush 

 river valleys where, in America, trumpet vine, wild grape, and five- 

 leafed ivy grow luxuriantly. 



The distribution of these forests depends on moisture, temperature, 

 and soil. In the main they occur in the moderately moist southern 

 part of the temperate zone, but are not well developed in sandy or 

 peaty soil. Specifically such forests occur in the United States mainly 

 east of the Mississippi River except for evergreens in the Appalachian 

 Mountains and a southeastern belt of conifers ; in Eurasia they occupy 

 a belt from northern Spain to southern Sweden, west through Siberia 

 into Japan; South Africa has a small deciduous forest, as has eastern 

 Australia, New Zealand, and the southern tip of South America. This 

 formation is of relatively little importance in the southern hemisphere. 



There are usually fewer strata than in the tropical rain-forest. 

 In the eastern United States, chestnut, walnut, oak, hickory, and tulip 

 trees represent more southern types, and birches, beeches, and sugar 

 maples are more northern. Hemlocks and other evergreen trees may 

 be intermixed locally with the hardwoods. 



Many of the terrestrial mammals in this region have subterranean 

 dens; among these may be mentioned the fox, bear (now largely 

 absent), skunk (an invader from the tropics), chipmunk, and shrew. 

 Wapiti, bison, Virginia deer, and beaver formerly ranged throughout ; 

 only the deer and a very few beaver remain. Muskrat, beaver, otter, 

 and mink belong to the forest near streams; the cottontail rabbit, the 

 jumping mouse, the raccoon, and the burrowing woodchuck, Marmota 

 monax, belong in the forest margin. Squirrels, flying squirrels, and 

 bats compose the arboreal animals. In all, Seton 49 lists 13 species of 

 mammals that are mainly arboreal, 18 that belong to the ground 

 stratum, and 3 that are mainly burrowing forms. The opossum and 

 porcupine in North America are unrepresented in the Old World. 



Among birds, the great horned owl, several hawks, the great crested 

 flycatcher, various thrushes, and woodpeckers, are characteristic of 

 the north temperate forest in America. Turtles are present around the 

 forest ponds and streams, and the black chicken snake, a constricting 

 species, may drape itself over bushes along the forest margins. The 

 timber rattlesnake and the copperhead are the poisonous snakes of 

 the region. Plethodon, the woods salamander, lays its few large-yolked 

 eggs in moist places under decaying logs. Tree frogs and Rana sylva- 

 tica are also characteristic inhabitants. The invertebrates of such for- 

 ests include burrowing earthworms, millipeds, snails, and land isopods 

 of the forest floor, a restricted termite fauna, and wood-boring larvae 



