"Why is the World Green?" by Alexander Gershenson is an excerpt from "The Where, The Why, and The How: 75 Artists Illustrate Wondrous Mysteries of Science" [Chronicle, $24.95], edited by by Jenny Volvovski, Julia Rothman, and Matt Lamothe:
The earth is green. Almost anywhere you look, plant matter is abundant. From tropical forests to high altitude deserts, plants reign supreme. And therein lies the question. Why isn’t all this seemingly readily available food being eaten much faster than it is? The world is not overrun with squirrels or rabbits because their population numbers are controlled by their predators, so why aren’t plants being better controlled?
Several hypotheses have been proposed to explain the “Green Earth” question. Some researchers suggest that plants are very good at being unpalatable and that a myriad of chemical and physical defense strategies are responsible for plants being very good at resisting predation and staying one step ahead of adaptations developed by herbivores to overcome such defenses. Recent experiments in which top predators have been excluded from the food chain show that the earth may, in fact, be green because top predators keep the herbivore population low, and consequently reduce the herbivory pressure on plants.
The complete explanation is likely to involve a combination of the two hypotheses, with plants continuously edging out herbivores in an evolutionary arms race of better and better defense mechanisms, as well as top predators ensuring that the herbivore population remains relatively small.
Check out these 9 science-inspired illustrations from the book: