We know of several copies of the seminal reference book - Biotic Communities, Southwestern United States and Northwestern Mexico - that have worn out, riding around for years on the dashboards of pickup trucks. The Boyce Thompson Southwestern Arboretum in Arizona, which published the book in 1982, sold out its stock of 10,000 copies and ever since, the book has been getting rarer and rarer among its audience of resource managers, teachers, researchers and plain old desert rats. Now the University of Utah Press has recognized a need and reissued Biotic Communities with an updated bibliography and an improved, blanket-sized map showing where 30 different plant communities occur in the region. From dense Sinaloan thornscrub to arctic-alpine tundra, the plant communities are analyzed in the book, documented with photos and sketches, and put in terms of evolution. Editor David E. Brown traipsed the region doing decades of field work for the Arizona Department of Game and Fish. Chapters were written by the region's top natural scientists. If you wonder how to recognize the transition from Sonoran to Chihuahuan desert (the saguaro cactuses drop out, the washes take on the look of gashes) or which reptiles prefer riparian deciduous forests (Sonoran spiny lizards and tree lizards), this technical and precise book will be useful. The oversize 342-page paperback costs $24.95, the separate wall map $15, plus $3.50 shipping, from University of Utah Press, 101 University Services Building, Salt Lake City, UT 84112 (800/773-6672).