Invertebrates are too numerous and varied to he 

 mentioned specifically (see Chapter 9). Snails and 

 slugs are especially ahundant in the moist mixed 

 mesophytic forests of the southern Appalachians, but 

 decrease in abundance and variety as the forest be- 

 comes drier and approaches the prairie (Shimek 

 1930). Millipedes are numerous in the rich humus 

 of the forest floor. Insects and spiders are repre- 

 sented by a multitude of species in all strata. 



yOrth Uru'rii-an >/<■( iV/koh.s 

 jorvst-vtliif biixiation 



Eastern North America, prior to white colo- 

 nization, had thousands of kilometers of contact 

 between deciduous forest and prairie, with tongues 

 of forest e.xtending far into the prairie along the river 

 valleys. Deciduous forest even bordered the prairie 

 on the north where the as])en grove ecotone intruded 

 in front of the boreal forest. A characteristic forest- 

 edge ty])e of vegetation and distinct animal commu- 

 nity occurs along these contacts and where the forest 

 confronts ocean or large lakes. The forest-edge com- 

 munity also permeates the deciduous forest in the role 

 of a serai community or biocies on rock, sand, aban- 

 doned fields, and around water (Chapters 8, 9). 



A different faciation of the forest-edge biociation 

 occurs west of the Great Plains. As the interior of 

 the continent grew arid in the Miocene and Pliocene, 

 many species of deciduous trees together with 

 their associated animals were able to persist in local 

 habitats throughout the western part of the country. 

 A distinct plant community — riparian woodland — of 

 willows, cottonwoods, sycamores, aspens, alders, and 

 other broad-leaved deciduous trees presently occurs 

 along streams, bodies of water, and elsewhere. It ap- 

 pears to be serai to coniferous forest or woodland 

 over most of the West, but reaches out into grassland 

 and desert in a manner similar to the tongues of 

 forest in the East, thus greatly extending the linear 

 distance of the forest-edge. 



The animal species composition reflects the rela- 

 tionship obtaining between the riparian woodland in 

 the \\'est and the forest-edge community in the East. 

 Xearly half of the species listed below pervade both 

 faciations, albeit represented by different subspecies. 

 Several species are confined to one or the other facia- 

 tion as indicated. Speciation among forest-edge 

 forms was doubtless encouraged by the virtual isola- 

 tion of both faciations when the grassland biome 

 evolved. Common species (Ingles 1950, Miller 1951) : 



Mammals 

 Eastern mole (I-'ast) Long-tailed weasel 



Gray wolf Wapiti 



Red fox Mule deer ( West ) 



White-tailed deer ( East) Eastern cottontail 

 Fox squirrel (East) (East) 



Woodchuck (East) Striped skunk 



Birds 



Turkey vulture 

 Sharp-shinned hawk 

 Cooper's hawk 

 Red-tailed hawk 

 Swainson's hawk (West) 

 Red-shouldered hawk 



(East) 

 Sparrow hawk 

 Bobwhite (East) 

 Mourning dove 

 Yellow-billed cuckoo 

 Black-bellied cuckoo 



(East) 

 Screech owl 

 Common nighthawk 

 Chimney swift (East) 

 Ruby-throated humming- 

 bird (East) 

 Hummingbirds (several 



spp., West) 

 Red-headed woodpecker 



(East) 

 Yellow-shafted flicker 



(East) 

 Red-shafted flicker 



(West) 

 Eastern kingbird (East) 



Western kingbird 

 (West) 



Cassin's kingbird (West) 



Barn swallow 



Violet-green swallow 

 (West) 



Common crow 



Blue jay (East) 



Black-billed magpie 

 (West) 



House wren 



Catbird (East) 



Brown thrasher (East) 



Eastern bluebird (East) 



Robin 



Chestnut-backed chicka- 

 dee (West) 



Cedar waxwing 



Loggerhead shrike 



Starling 



\\'arbling vireo 



Bell's vireo (West) 



Yellow warbler 



Yellowthroat 



Yellow-breasted chat 



Brown-headed cowbird 



Bullock's oriole (West) 



Temperate deciduous forest biome 297 



