Having fun with ecology. I was explaining the difference between aspens and birches. They really are not very similar except they both have whitish bark. The aspen bark does not peal; birch does. Birch are also much more often multiple stems. Aspen tend to go straight up. Aspen leafs shimmer in the wind; birch not so much.
You can see the difference in the pictures. Picture #1 shows both. The birch is the whiter one. Picture #2 is a typical birch and #3 typical aspens. The last pictures shows some aspens. They do not typically lay down like that, but you can get a good look at the usual shape.