I will say, my favorite character was in fact a tree--the American Chestnut. I enjoyed learning about both its true history and how that tree's history was woven into the fictional life of one of the main characters. As the characters came together, the initial part of the eco-activism storyline reminded me of my own time last summer in California's redwood forest and of Julia Butterfly Hill. An added piece of connection--I read much of the 500-page tome outside, under the trees of my own backyard.
These two book reviews and Richard Powers' website are great places to learn more.