Lee,
From my relative short experience, Aerials show so much, but you also have to decipher what you are looking at. (Meaning the site and all of its contours and natural shapes and forms.)
Yes. it will show trees, but some of those trees are going o be giving off shadows, making them look much bigger then they actually are. It would serve you best to try to really look deep and study all of the images with ones from on the ground and hopefully come to more solid conclusions.
www.mapquest.com is now that website I'm using most for piecing together aerials. You can simply punch in the address of the club or course you want to look at and go from there. ONce you get the map, you just have to click on their Aerial photo tab for a color image that is usually pretty good.
Another site I found of interest, which will greatly help you is one based in England, which led to a program which you can downlad off the internet that allows you to zoom in easily as well as measure terraforms. I'll have to hunt it down for you, so email me so I can remember to get it for you!