I have attached a test map with a working War Club ability that doesn't destroy trees. You can press "Escape" in-game to alternate between the old and new War Club ability so you can compare the two. As far as I tested they look and feel exactly the same (which is a good thing) so don't be confused if you can't tell the difference.
If this causes problems then I'd say go with Halithor's solution. Both should work just fine. I just wanted to try and create a more visually appealing version, plus I was bored and this seemed like fun lol.