At around thirteen degrees south latitude, it passes to the west of Silman’s tree plots. In his plots, which collectively have an area roughly the size of Manhattan’s Fort Tryon Park, the diversity is staggering. One thousand and thirty-five tree species have been counted there, roughly fifty times as many as in all of Canada’s boreal forest. And what holds for the trees also holds for birds and butterflies and frogs and fungi and just about any other group you can think of (though not, interestingly enough, for aphids). As a general rule, the variety of life is most impoverished at the poles
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