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In the 1980's, Sierra Club Books came out with a series of Naturalist's Guides that included books on: The Piedmont of Eastern North America, North Woods of Michigan, Deserts of the Southwest, The Sierra Nevada and the two that I own - The North Atlantic Coast and The Middle Atlantic Coast.
Although these books are 30 years old, they are just as relevant and informative today as when they first came out. There are many newer books that describe the plants and animals of a region, but nowhere can you find a book that combines all of this information into a whole like these guides. Rather than listing a series of plants and animals and listing some of their atributes, these books describe how they interact with each other in describing how the ecosystem as a whole works.
When I want to identify a sea creature I look it up in one of my many seashore guides. When I want to know how it interacts with the creatures around it I open my copy of The North Atlantic Coast.
Unfortunately, these books are hard to find as new books, and when found usually are very expensive. However, used ones can be bought from Amazon for very little money. They are certainly worth having in your natural history library.