The best time to begin to study the trees is today!  The place to begin is right where you are, provided there is a tree near enough, for a lesson about trees will be very dull unless there is a tree to look at, to ask questions of, and to get answers from.  There is no time of year when there are not three or four of the important signs hung out on every tree to guide those who are trying to find out its name, and learn the story of its interesting life.

From the introduction