How do you make a unit 'harvest' a tree without damage?

[PsychoMagnataur]

I'm sure the answer is very simple, but I can't figure it out. How do I make a peasant use 'harvest lumber' on a tree, so that he swings his pick, holds wood, and the tree shakes, without dealing damage to the tree and lasting forever, almost as a doodad/effect?

 

[VGsatomi]

There are several different ``harvest lumber`` abilities on the abilities list. For example; human, orc, undead, ect. The night elf (whisp) version should do the trick.
-VGsatomi