Lumberjacking
Generally speaking, lumberjacking is the trade of collecting premium samples of wood from trees.
On Angel Island, the lumberjack is also able to harvest higher quality types of wood as skill training progresses. Lumberjacking also 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.
Training Lumberjacking
Lumberjacking can be trained from 0-GM by hiring a mercenary from the fighter pit in J'Helom. Buy 10 or 15 axes from the blacksmith and make a macro to heal your mercenary and to equip an axe if the one you're using breaks. It is recommended that you use a mercenary which is equipped with good armor and a shield for training against with such heavy weaponry.