586 



THE COMMUNITY 



daily abundant and characteristic, as are 

 a host of rodents and lagomorphs (Elton, 

 1942). Birds of many kinds are identical or 

 closely representative in the two major 

 areas of taiga. The crossbills (Loxia), 

 closely confined to the taiga of both hemi- 

 spheres, exhibit a remarkably eflFective 

 adaptation of the bill for extracting the 

 seeds from cones. 



The fresh-water communities of the taiga 

 are only slightly less well integrated into 

 the biome than in the tundra. In glaciated 

 Europe and North America, lakes of vary- 

 ing size and in varying successional stages 

 (p. 577) are especially characteristic of the 

 taiga zone, and may constitute areas of 

 water sometimes about equal to the amount 

 of intervening land. 



The continuous Siberian and Canadian 

 taiga biomes may each best be interpreted 

 as a single vast major community. Their 

 individual outliers, islands of taiga in grass- 

 land and deciduous forest, are to be inter- 

 preted as individual communities of vary- 

 ing extent. Such islands form one of the 

 modes of transition to the grassland com- 

 plex and to the deciduous forest biomes, 

 discussed previously with respect to eco- 

 tones (p. 476). How intimate the latter 

 transition may be is familiar in northeastern 

 North America, where taiga communities 

 may invade the adjacent biome of tem- 

 perate forest in association with slight 

 physiographic or edaphic difi^erences. The 

 transition from taiga to tundra is complex 

 in that the fresh-water components of the 

 two biomes are little diflFerentiated, and in 

 the graded transition of the forest through 

 dwarfed timber to a ragged "timberline" at 

 the limit of tree growth (p. 481). 



Like the tundra, the taiga has an enor- 

 mously important seasonal cycle conspic- 

 uous in the dormancy of its invertebrates 

 and of many vertebrates, and in the spring 

 influx and autumn departure of migratory 

 birds (p. 539). In these northernmost 

 biomes, indeed, bird migration forms a 

 link with more southern biomes, a link of 

 such far-reaching significance to commu- 

 nity metabolism as to recall the interde- 

 pendence of the ecological formations of 

 the sea. 



A curious minor physiographic inversion 

 of those taiga communities that interdigitate 

 with the grassland biome is to be seen in 

 parts of the Great Plains of western North 



America, where in canyons and ravines 

 forest may be entirely below the level of 

 the grassy plains and invisible at a dis- 

 tance, whereas elsewhere eminences (in- 

 stead of depressions) are climatically mod- 

 ified and conspicuously covered with conif- 

 erous forests. The problems involved in 

 the great southward peninsular extensions 

 of tundra and taiga in north-south moun- 

 tain ranges in North America, and the quite 

 different geographic arrangement of these 

 formations in Eurasia, conditioned by the 

 contrasting east-west and widely isolated 

 mountain ranges, require separate discus- 

 sion (p. 592). 



THE DECIDUOUS FOREST BIOMES 

 AND BIOME-T5fPE 



The temperate deciduous forest biome 

 of eastern North America has faunally and 

 florally allied counterparts in eastern Asia 

 and Europe, and to a lesser extent in 

 Western North America. These are now in 

 terpreted as the remnants of a once much 

 more continuous series of biomes, or per- 

 haps a single biome, of Cretaceous age. 



An intelligible definition of the decid- 

 uous temperate forest biome type is more 

 difficult than for the more nearly contin- 

 uous tundra and taiga. The beech-maple 

 climax forest (or its equivalents), the oak- 

 hickory forests, and the more complex hard- 

 wood forests of the Appalachian region 

 form merging groups of deciduous forest 

 types (Braun, 1916). This biome is con- 

 nected by interdigitation with the taiga, 

 and by forest river-fringe "peninsulas," and 

 "islands" with the grassland. A major diflR- 

 culty in assortment of communities asso- 

 ciated with this biome is the broad con- 

 tinuous area of pine land in the south- 

 eastern United States ( Shelf ord, 1926), 

 which resembles the taiga in some of its 

 vegetation, but the surrounding deciduous 

 forest in conspicuous elements of its fauna. 

 The coniferous forests at its northern bor- 

 der (white pine, hemlock, and so forth) 

 are no less a difficulty. Characteristic 

 among larger mammals of this biome in 

 North America are the Virginia deer (Fig. 

 221) and the black bear; among medium- 

 sized forms are the common opossum and 

 raccoon, and there are numerous character- 

 istic smaller mammal components among 

 the rodents and insectivores. Clements and 

 Shelford (1939) employ the red-backed 



