Changes in the Amount of Forest on the Great Plains
At the end of the last ice age,some 8,000 to 10,000 years ago, the climate was cool and damp,and a dense coniferous (evergreen) forest occupied the Great Plains,the vast region stretching from Alberta,Saskatchewan,and Manitoba in Canada south through Texas.A dark mantle of spruce trees extended from what are now the Canadian prairies south through the Dakotas into the central states of the United States,while pinewoods appear to have flourished on the southern plains of the United States.But as the chill of the glaciation gradually lifted,the climate eased into a drier and warmer phase, marked by more frequent droughts,and the forest was forced to retreat to the north.Within a remarkably short time,the forests of the Great Plains either surrendered directly to grasses or else gave way first to deciduous trees (trees that lose their leaves seasonally)and then to prairie grasses.
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