In Trees, the author of On Trails turns his attention to biology, adopting the tree as a lens to view the world and embracing “treethinking”—slow, branching, deep-rooted, long-viewed—as a path to wisdom. He pushes the idea everywhere, and the reporting earns the reach: scaling a sequoia with David Attenborough, studying Kimura’s famous bonsai garden in Japan, sleeping in a chimpanzee nest in Tanzania, then working through Alabama archives into his own family’s slaveholding past. Moor’s prose is clear, curious, unafraid of contradiction. Arborescence is the organizing metaphor, and by the fourth or fifth application—brains, evolution, race, grief—it starts to strain; not every subject wants to be a tree. But the range is his point, and this big, ambitious, generous book mostly earns its size.