Ludwig van Beethoven was a tree-hugger. “The woods, the trees and the rocks give man the resonance he needs,” wrote the composer, who was known to embrace his backyard linden. Walt Whitman warned that in the absence of nature, the “pestiferous little gratifications” of the city wouldn’t be enough to sustain us. And John Muir worried that his fellow citizens, if not regularly exposed to open land and sky, would become “tired, nerve-shaken, over-civilized people.” All three men sensed what science is increasingly proving: Being in nature nourishes our minds and bodies, and its absence makes us unwell.

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