I just... I don't know. I've been using this avatar for, Jesus Christ, two years now? Not for two years straight, but it's definitely been my avatar for most of that time, first at INFPgc, and now here. I don't know. I just love it. I don't even know why I first picked it. Probably because it jived with my mood at the time, as Bluebell said. After a while you just stop noticing your avatar, especially if you rarely change it. But since I've been recently looking for a new avatar, I've really started to admire this one.
I like the low-angle view, the vibrant colors (god, the green), the girl's expression, and the tree's many many branches stretching strong and sturdy overhead.
What I kind of always imagined was that the girl was like the tree, or that the tree was like the girl. I kind of always saw the the tree stretching overhead as hinting at the immense wisdom and strength inside of her.
Yeah, I'm just that, um, hilariously poetic.
Since I may change my avatar soon, I'll post my current avatar for posterity's sake:
Eh, I don't feel like searching my computer for the resized one, really. Do I? Nah.
They're running just like you
For you, and I, wooo
So people, people, need some good ol' love