You'll probably find many examples. Some bark is used for floats and bulletin boards. Come summer, you'll be glad for the shade that trees offer, too. You can record variations in bark patterns by making rubbings. Peel the paper-covering off the crayon and hold it horizontally.
Smooth barks are easiest to rub, and steady one-directional strokes work best.
If the paper keeps shifting, tie it to the tree. You can bind your rubbings in a scrapbook, or frame them to hang on the wall. Include rubbings in the diary that you are keeping of a single tree. Never strip bark from trees, as that may damage or even kill a tree. You can collect bark off of fallen branches and stumps.