Book Review

Check out the text out of this book: The Sibley Guide To Trees     Author: David Allen Sibley

As you can see straight from the text in the book it is working into the part where it is classifying the different types. Later on in the book they also talk about how some trees could be considered shrubs and some shrubs trees. I guess there is no real defined lines, but enjoy this below. 

"In theory, the term subspecies should be used for well-defined variation that nearly rises to the level of species, while variety is used for somewhat less well-defined variation with differences that are relatively small or inconsistent. In practice, however, the distinction between subspecies and variety is often unclear and arbitrary. and many authorities now advocate making variety a synonym of subspecies. trees. In a few cases common names have been modified to distinguish them more clearly from other species A few of the most commonly used alternate names are listed in each species account beneath the scientific name. 

SIZE AND MEASUREMENTS 

The maximum size listed in the species accounts in this guide are for the maximum height recorded in North America and has been compiled from several sources. Seeking and documenting big trees is a popular hobby, and the official “National Register of Big Trees” is maintained by the organization American Forests."