. Animal Ecology. Animal ecology. its half-life is 5760 years. The age of any sample can be determined on the basis of the extent to which it has degenerated (Libby 1960). The clisi-n- As the glacier retreated, vast areas were freed for reinvasion by plants and animals (Adams 1905, Gleason 1922). The land must have been a barren, sterile expanse of raw parent soil material, deficient in nitrogen. The first plants to invade were jirobably species the root nodules of which l)ore bacteria, fungi, or actinomycetes capable of fixing nitrogen from the air, thereby enriching the soil (Lawrence 1958).
. Animal Ecology. Animal ecology. its half-life is 5760 years. The age of any sample can be determined on the basis of the extent to which it has degenerated (Libby 1960). The clisi-n- As the glacier retreated, vast areas were freed for reinvasion by plants and animals (Adams 1905, Gleason 1922). The land must have been a barren, sterile expanse of raw parent soil material, deficient in nitrogen. The first plants to invade were jirobably species the root nodules of which l)ore bacteria, fungi, or actinomycetes capable of fixing nitrogen from the air, thereby enriching the soil (Lawrence 1958). The recession rate of the glacier was probably faster than the advance of vegetation and animal life. A belt of tundra developed ; coniferous forest broadened to a much greater width than existed at the peak of glacia- tion. Deciduous forest, requiring a better soil, ame- lioration of climate, and competitive displacement of the already established coniferous forests, moved northward rather slowly. There is evidence that this northward movement of the biota is still in progress, and that the great belts of vegetation are not yet stabilized in respect to each other and to the climate. Fossil or pollen evidence for the existence of tundra along the retreating glacial front is scant in North America, except for certain areas in Maine; existence of tundra is better established in Europe. Special difficulties are involved in the identification of tundra pollen in core samples from bogs. Further- more, deep kettles in which bogs later formed sus- tained large blocks of ice, well insulated by being nearly buried in glacial till, for a long time after the main mass of ice had withdrawn northward. De- posits of pollen could not settle in the kettles until the ice blocks had melted, which was usually not until spruce-fir coniferous forests had become the pre- vailing vegetation of the region. This is doubtless the reason for the almost universal occurrence in North America of spruce-fir
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
