22 



Geographic 



Distribution of 



Communities: 



Temperate 



Deciduous Forest 



Biome 



In tliis and the follouiiif; cliaptcrs wc will try to 

 gain an understanding of tiif geographic distribu- 

 tion of animals as it occurred in primeval time before 

 the colonization of the continent by white man, using 

 bionies as our units of analysis. Kach biome will be 

 considered in resjKCt to its distribution, vegetation, 

 and plant associations ; the constituents of its various 

 biociations ; the relative abundances of the principal 

 animal species, especially mammals and birds ; the 

 adaptations and adjustments, especially behavioral, 

 to the biome as demonstrated by the predominant 

 animals ; and human uses made of it. We will devote 

 most of our study to biomes of North America, but 

 the rest of the world will not be neglected. A genera! 

 reference which the reader will find invaluable is The 

 Naturalist's Guide to the Americas (Shelford 1926). 



The temperate deciduous forests of North Amer- 

 ica, western Europe, eastern China, and Japan are 

 related as developments of the Arcto-tertiary flora 

 which at one time was practically continuous around 

 the world in North Temperate climates. In North 

 America, the deciduous forest is best developed in 

 the Eastern United States, although elements of it 

 are mixed with conifers in the North, West, and 

 through the mountains of Mexico into Guatemala 

 (Sharp 1953). The deciduous forest of southern 

 Chile is derived from the Antarcto-tertiary flora, dis- 

 cussion of which we must forgo. 



Mean annual precipitation for the biome in North 

 America varies from 75 to 125 cm (30-50 in.) ; mean 

 annual precipitation for the Gulf states is occasionally 

 as high as 150 cm (60 in.). For the most part, rain 

 falls periodically throughout the year ; in many places, 

 precipitation also falls as snow in wintertime. Mean 

 monthly temperatures from North to South vary 

 from January minima of — 12° to 15°C (10° to 

 60°F) to July maxima of 21° to 27°C (70°to80°F). 

 Average mid-day relative humidities during July 

 range from 75 per cent in the East to 50 per cent 

 where the biome contacts prairie in the West. The 

 annual frost-free period varies from about 150 days 

 in the North to as much as 300 days in the South 

 (Kincer 1941). 



The climax of the deciduous forest biome is a 

 community dominated by broad-leaved trees that are 

 leafless during the winter over most of the area. In 

 the South, the dominant trees are mostly evergreen. 

 The trees usually form relatively dense forests with 

 a closed canopy, but where the biome verges on 

 prairie, the forest gives way to savannas containing 

 scattered groves. The shrub stratum is often but 

 poorly developed within the forest because of the 

 deep shade there, but is well-formed at the forest- 

 edge. The herb stratum has a rich variety of flower- 

 ing plants, which are especially conspicuous in the 

 spring. All seasonal aspects are well defined. The 

 leaves of the trees and shrubs, as well as those of most 



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