Wanted: General introductory book on trees

[Mike B in OKlahoma]

I have a friend who has asked me for advice on a good introductory book to trees. Target audience is an intelligent adult with no science background. I'm hoping to point to one that indicates "how trees work" in terms of how they function internally, plus perhaps explain their role in the ecosystem. This may be a bit much to ask for in an layman's book, I realize.

I'm clueless about anything that doesn't have a pulse. Can anyone recommend a readily-available book?