No matter where you stand on hot-button environmental issues such as global warming, overpopulation, conservation and sustainability, you need to understand the concepts before you can join the discussion.

“Ecology: A Pocket Guide” is an accessible little book that spells it out, from A to Z.

Originally written by ecologist Ernest Callenbach in 1998, the revised edition of “Ecology” explains more than 60 basic concepts in understandable terms.

Callenbach describes the book as reader-friendly. It’s designed so the reader can “dip into it, lay it down or put it in a pocket, and come back to it later.”

Consider this passage on decomposition. “At first thought, it may seem sad that living beings die and decompose. But without death and decay, there could be no new life. If it were not for the breaking down of organisms into nitrogen, carbon and sulfur, and their other component substances, the planet would be littered with dead stalks, leaves, and carcasses. Your compost pile wouldn’t be able to turn kitchen scraps into rich garden humus. New growth would be impossible and animals like ourselves would find nothing to eat.”

Something to chew on.

Callenbach is the author of “Ecotopia,” which has sold nearly a million copies, “Bring Back the Buffalo” and “Ecotopia Emerging,” among other books. He lives in the San Francisco Bay Area.

Published by University of California Press, “Ecology” is a 192-page compact softcover. It retails for $13.95.

Contact: www.ucpress.edu or 510-642-4562.