I'm not Really obsessed with brushes today.. (well maybe a little) but I found a stock photo of this great tree and I want to make a brush from it. However, I'd like it to have some sort of soft edge.. rather than the hard edges of the photo. Or maybe just a brush of the tree itself. I've no idea how to do the later, I've never worked with layer masks, but from the thread I read a few minutes ago that sounds like it might be the way. Here's the photo. I'd love to hear your suggestions on how this might be done, or suggestions of where to look for tutorials that might get me there. 

Thanks

Myst