What is the importance of the Bialowieza Forest in the nonfiction book, The Zookeeper’s Wife?

The Bialowieza Forest is an ancient forest near Warsaw. Today, it is a natural preserve and home to the re-created species of tarpan horses and aurochsen cattle. These species were extinct, but were re-created through the efforts of the Nazis, including Lutz Heck, who had an interest in back-breeding animals to create a “pure” animal.