Nathaniel Tarn’s newest collection of poems, Ins and Outs of the Forest Rivers, dives deep into the spiritual and physical sufferings of our global age. After a moving overture, the book unfolds in five sections: “Of the Perfected Angels,” with its lucid meditation on Issenheim altarpiece by Matthias Grünewald; “Dying Trees,” written out of the horrible loss of hundreds of thousands of trees throughout the American West in recent years; “War Stills,” an engagement with the ongoing atrocities in Iraq; “Movement / North of the Java Sea,” taking flight from Maui to Bali to Papua New Guinea; and the final section “Sarawak,” snaking its way through the river and indigenous anguish of Borneo, where Tarn as poet-anthropologist surveyed the loss of forest lands and its effects on tribal peoples.