Two Blonde Guys Digging & Filling Holes

There were two blonde guys working for the city. One would dig a hole -- he would dig, dig, dig. The other would come behind him and fill the hole -- fill, fill, fill.
These two men worked furiously; one digging a hole, the other filling it up again.
A man was watching from the sidewalk and couldn't believe how hard these men were working, but couldn't understand what they were doing. Finally he had to ask them.
He said to the hole digger, "I appreciate how hard you work, but what are you doing? You dig a hole and your partner comes behind you and fills it up again!"
The hole digger replied, "Oh yeah, must look funny, but the guy who plants the trees is sick today."