I've just heard that "book pairing" is a thing. Evidently you can pair books with all kinds of things. This business of pairing fiction and nonfiction books is interesting.
And Nancy Castaldo's pairing of nonfiction and eco-fiction children's books at Nerdy Book Club is particularly interesting. Notice that she pairs Ivan: The Remarkable True Story of the Shopping Mall Gorilla by Katherine Applegate with The One and Only Ivan also by Applegate.
I don't believe I've included animals in our environmental books. Castaldo's thinking is that the animals in the books she's suggesting are endangered or, in Ivan's case, not living in its natural environment. I can certainly accept that as a reason to include those kinds of books under the "environmental" umbrella.