Lumberjacking

On Angel Island, lumberjacking adds a bonus modifier to damage while using 2 handed axes.

The bonus is 10% of the lumberjack skill up to 99.9, and 20% total for 100 skill.
+1% bonus for every 10 points of lumberjacking.
+10% bonus at Grandmaster.

So at GM Lumberjacking you get a 20% total bump in damage.