poppy, i honestly never have differentiated between an aspen and a birch, and believe me i have been around both a lot. i guess some people just know these things (you) and some people just kind of never notice (me). however i think i can tell the dif between a tree trunk and an elephant trunk. the elephant trunk tends to move around and smell you.
...I don't know if you can tell a trunk of a tree from an elephant's trunk, but if you saw a birch tree and an aspen side by side, you would be able to tell the difference, too! ;-)
