There are more than 400 species of oak in the world, and more than 80 in North America, where it is one of the mainstays of American hardwood forests. Since pioneer days, oaks have provided food, dyes and timber in vast quantities. Though it's easier to identify species of oak from the shape of leaves, you can also identify them from the color and texture of their bark, which varies widely from one species to another.
Start your identification project in the fall by learning the basic shapes of the oak leaf and its seed, the acorn. Most oak leaves have deeply serrated edges, and acorns are small, brown and capped. Zero in on the bark when you're fairly certain you're looking at an oak tree, and not some other species.
Snap a picture of the bark when you come upon an oak tree. Note the color and texture of the bark. For example, a mature black oak has deep ridges in bark that is nearly black. A live oak has smoother bark that's brown with a touch of red. Jot down notes on color, texture and the shape of the tree's limbs.
Go to your local library and ask for a book on oak tree varieties. Compare your picture to the photos or illustrations until you find a match. Search by the climate and growing conditions in your area to narrow the possibilities. For example, don't bother researching live oaks if you live in a northern climate.
Create a database by uploading bark pictures into the software program of your choice, and adding notes. You'll quickly learn to identify oak trees by their bark, in summer or winter.