All you can do is try and see what happens. Before you install anything too permanent or drill holes, it might be a good idea to do a mock up installation just to see what kind of reception you'll get thru those trees. I don't know why but I when you mentioned trees, I pictured a single fence row. LOL!
Moving west away from them and capturing the signal as it comes over the tops of the trees is probably your best bet unless you can truly get the antenna above them.
Here is some good reading regarding signal diffraction. Also check the links at the bottom of the page. Good luck!!
http://www.hdtvprimer.com/ANTENNAS/siting.html