Where exactly was the tree? There's something brownish in the right part of the front wheel that could be a tree trunk in the background but it could also bee some kind of light reflection, I am not sure. The rider appears compressed horizontally, I assume this is caused by subject velocity and shutter speed (or is it caused by the angle from which you took the shot?), is there any way to avoid this effect? There are several grey "stains" in the left part of the image, probably only visible with relatively bright monitor settings, but worth cleaning out anyway as they distract from the racer.
I like the way you've done this, the way you've used the flash give it a great sense of motion and speed. I can never quite get this sort of shot right, so I take my hat off to you, this is very well done.
0 
{K:24381} 10/16/2004