Botany for Gardeners. Revised Ed. Brian Capon (Timber Press, 2005). An excellent introduction.
Bringing Nature Home: How Native Plants Sustain Wildlife in Our Gardens. Douglas W. Tallamy (Timber Press, 2007). Native insect herbivores can't eat non-native plants! Beautiful photographs illustrate this heartfelt plea for more native plants in the garden by an accomplished entomologist.
There is now a revised second edition available.
The Carbon Age: How Life's Core Element Has Become Civilization's Greatest Threat.
Eric Roston (Walker, 2009). Wanted to know more about the carbon cycle. Found this book. Worth reading.
Forest Trees of Illinois. Robert H. Mohlenbrock (Illinois Department of Natural Resources). Very good and complete, with natural habitats shown by county.
Food Not Lawns: How to Turn Your Yard into a Garden And Your Neighborhood into a Community. H. C. Flores (Chelsea Green, 2006). A gardening book for radical gardeners. Some people are put off by its "preachiness," but not me. Like Gaia's Garden, Oregon-centric, so not all advice is not practical for our region.
Gaia's Garden, Second Edition: A Guide To Home-Scale Permaculture. Toby Hemenway (Chelsea Green, 2009). A classic. Good advice on methods, though West Coast-centric so not all recommendations are suitable for the Midwest.
Land of Big Rivers: French and Indian Illinois, 1699-1778. M. J. Morgan (Southern Illinois University Press, 2010). Environmental history of the land and peoples along the Mississippi between the Missouri and the Ohio Rivers.
Landscaping With Native Trees. Jim Wilson and Guy Sternberg (Houghton Mifflin, 1995). An outstanding book with excellent photographs and informative text.
A Natural History of the Chicago Region. Joel R. Greenberg (University of Chicago Press, 2002). A sort of companion to Nature's Metropolis that focuses on local ecosystems.
Native Trees for North American Landscapes. Guy Sternberg and Jim Wilson (Timber Press, 2004). Updated and more complete and in depth than Landscaping with Native Trees.
Nature's Metropolis: Chicago and the Great West. William Cronon (W.W. Norton, 1992). A discussion of how the growth of Chicago affected the surrounding regional countryside by a great environmental historian.
Plants of the Chicago Region. 4th Ed. Floyd Swink and Gerould Wilhelm (Indiana Academy of Sciences, 1994). A compendium of every recorded species of wild plant native to the Chicago region.
Of Prairie, Woods, and Water: Two Centuries of Chicago Nature Writing. Ed. Joel Greenberg (University of Chicago Press, 2008). Short and long selections, first-person accounts of the Chicago wilderness and how it changed over the years.
The Prairie Spirit in Landscape Gardening. Wilhelm Miller (University of Illinois, 1915; Reprint edition, University of Massachusetts, August, 2002). Old yet timely advice by the man who invented the term "prairie style" as he advocated for using native plants and naturalistic designs.
A Sand County Almanac (Outdoor Essays and Reflections). Aldo Leopold (Ballantine, 1986). There are several available editions of this seminal work by one of the foremost American conservationists. These essays distil his thought in poetic fashion. A life-changing book.
Secrets to Great Soil. Elizabeth Stell (Storey Publishing, 1998). How-to with simple instructions.
Thinking in Systems: A Primer. Donella Meadows (Chelsea Green, 2008). Ever wonder about why an ecosystem is called that? What a feedback loop is? This book explains how system theory works, in clear language with good diagrams.
Underground: How Creatures of Mud and Dirt Shape Our World. Yvonne Baskin. (Island Press, 2006). Well written discussion using current scientific research to explain soil ecosystems for the interested layperson.
Win-Win Ecology. Michael L. Rozensweig. (Oxford University Press, 2003). Describes the principles of reconciliation ecology.