In Book 6, Leah uses multiple literary devices (metaphor, simile, personification, imagery, and idiom) to explain the natural environment of the Congo and the unique farming techniques it requires:
Clearing a rain forest to plant annuals is like stripping an animal first of its fur, then its skin. The land howls. Annual crops fly on a wing and a prayer. And even if you manage to get a harvest, why, you need roads to take it out! Take one trip overland here and you’ll know forever that a road in the jungle is a sweet, flat, impossible dream. The soil falls apart. The earth melts into red gashes like the mouths of whales. Fungi and vines throw a blanket over the face of the dead land. It’s simple, really. Central Africa is a rowdy society of flora and fauna that have managed to balance together on a trembling geologic plate for ten million years: when you clear off part of the plate, the whole slides into ruin.
This description of the jungle helps the reader understand how its composition influences farming and life in the Congo. The visual imagery of red soil, fungi, and vines allows us to imagine this elaborate and fragile balance of plants and animals. Leah personifies the jungle, first with simile in which she compares "clearing a rain forest" to "stripping an animal first of its fur, then its skin," which indicates how abhorrent she finds deforesting. The personified land "howls," has a face, and can die. Another simile compares the destroyed soil to "the mouths of whales." Metaphorically, "fungi and vines throw a blanket" over the destroyed earth. Finally, the "rowdy society of flora and fauna" evokes a crowded, lively, and barely cooperative community.
Leah also uses the idiom "fly on a wing and a prayer" to describe the often unsuccessful attempt to grow annual crops. (As opposed to perennial plants, annuals must be replanted each harvest, so they are not permanent parts of the land.) To fly on a wing and a prayer means to attempt something that will probably not succeed, like a plane landing with only one wing left.
She metaphorically calls this ecosystem a "trembling geologic plate." This is also literal, since Africa (like all continents) is shaped by the movement of tectonic plates. But the plate becomes metaphorical when Leah describes deforestation in the Congo as "[clearing] off part of the plate" and creating an imbalance. This imbalance causes the plate to tilt and everything to fall off, just as deforestation hurts the rest of the environment in the Congo.