Its natural geographical distribution existed in a distinct southern limit closely related with the eminent factor such as the annual mean temperature.

它的自然地理分布存在明显的南缘界限，而分布的南限因子主要与年平均温度有关。

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Plant ecologists know that the northern limit of the forest is determined by the mean July temperature.

FORBES: Global Warming: Hotheads, Flatliners and Lukewarmers, Part One