The guard was probably added to fight Woodcutting bots, as they would get stuck trying to chop down this tree. Upon completion of the quest Love Story you can visit this guard and he will ask for you to chop the tree down, stating that his reconnaissance mission is completed. When cut from the tree he will award you 5,000 coins. You have the option to tell him "Sorry I am busy." "Come again soon, I'm not going anywhere," he will reply. If your inventory is full, he will suggest you make space for the reward he wants to give you. While cutting him from the tree he will yell in pain as you miss and hit him from time to time. The once "Guard in tree" will remain as a stump once you have done this optional task.