Peter Thomas wrote this book because he teaches about trees and he couldn't find a textbook that he liked. This book clearly fits that particular niche. It's intended as an introductory text for undergraduates, so it's also written at an appropriate level for the general reader.
You'd expect it to be boring, but it isn't. He presents the material in a lively and interesting fashion. Thomas starts with food production (leaves), water transportation (trunk and branches), and the scaffolding that holds a tree up. Along the way, you'll find answers to all those questions that three year olds might ask their parents - - how does the bark stretch when a tree adds a ring? How do apple blossoms turn into apples? Why do quaking aspen leaves quake?
If those questions interest you, you'll enjoy the book. It's organized conceptually and analytically, not around those kinds of questions, but you'll learn the answers along the way. You'll also learn all sorts of other things.
Because Thomas intended it for classroom use, by the later chapters he regularly cross-references concepts and processes that he introduced at the beginning of the book. I'd forgotten some of them, and that was frustrating. If I had been taking a class on trees, my teaching assistant or professor could have clarified, and Thomas clearly wrote the book on the assumption that readers would have such people available. In a revised edition, more gentle reminders for the general reader would be helpful. A glossary of terms wouldn't hurt either.
All in all, though, it's a very good book - - I'd give it a 4.5 if I could. Enjoy.