For many generations, the hardwood forest resource has had the more desirable timber cut while leaving the smaller and less desirable trees. With each successive harvest the quality of the residual timber is reduced and today there are thousands of acres growing "green junk".
Granted, most birds and other wildlife don't care whether or not a tree is straight and sound (many would prefer "green junk"). However, growing a well-formed, quality oak not only keeps them (the wildlife) happy, but growing a well-formed, quality oak also keeps the landowner happy by providing potential income and other benefits.