Horticulture books

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Looking for some good books on Mugo pine, hackberry, Amur maple etc. I know these are specific but if I could find any specifics for these it would be great.

If not I am interested in learning how and why things happen with trees. I have learned a lot through practice with trees but I would be interested in getting a deeper and broader understanding of bonsai as an art and a science. Thanks for the help