The history of forests

During the ice age, since there was no mountain ridge in north America to stop ice from moving forward (the main ridges, the Rocky Mountains and the Appalachian Mountains, run north to south), ice moved south, causing temperate forests to withdraw. In Europe, instead, the Alps and the Pyrenees prevented ice from moving forward, thus stopping forests from moving away from the north. Many species of plants could not spread too much because of the glaciers moving powerfully forward, and so they disappeared. Chinese forests were spared the advance of the ice and the consequences of the ice age, thus preserving even more vegetal species than Europe. Asian and European eastern forests must have formed an uninterrupted belt; even now both areas have some species of trees in common, for instance the Caucasian walnut tree, of which 8 varieties are now known in the world, of which 7 are in China and Japan and one in the extension towards the Caspian Sea of the biome of Iran’s temperate forest. Before the ice age, this tree was widespread in all the deciduous forests of Europe, as is shown by the finding of fossil pollen. After the glaciations, the Caucasian walnut tree became rare in the West, where it only survived in the deciduous forests of Iran, acting as a sort of connection with the flora of the temperate forests of the Far East.

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