Answer: Birch are so difficult to prune well for shape and so prone to insect problems provided entry by the cuts that it is generally suggested not to prune them if at all possible. To be honest I don't know of a book that could show you how to begin to try to prune it for shape. In the long run this tree will continue to grow and it will likely be very obvious that it has been narrowed. You might wish to hire a professional arborist (not just a tree trimmer) to consult with and help you determine if it can even be done. Good luck with your tree!
Q&A Library Searching Tips