BOOK REVIEW of Greenwood, by Michael Christie. Imagine that you’re a humble woodland guide, working for pitiful wages at an island resort northwest of Vancouver, British Columbia. The year is 2038, and Greenwood Arboreal Cathedral, as it’s called, is home to “one of the last remaining old-growth forests on Earth.” Most of the world has succumbed to dust storms and “rib retch” (a new strain of tuberculosis) following a “Great Withering” from spreading “fungal blights and insect infestations. …That’s the setup for the Canadian writer Michael Christie’s new novel, “Greenwood,” a time-hopping, globe-circling picaresque with apocalyptic themes. …Even the book’s most ruthless old-growth exploiter has his moments of epiphany… “It’s strange, isn’t it … how one only needs to purchase the land on which such a thing is rooted, before one is permitted to destroy it forever?”