Getting to the root of the problem...

Gallileo once said "if you give me a lever long enough I shall move the earth". Unfortunately, the levers in this case were no longer than 7 feet. 
After an epic battle of man vs. nature, Joe and Jeff (our feller in residence) secured a narrow victory over 4 willow tree stumps. They hacked at the trees all day and then they were gone.

How did they do this I hear you ask:
1) Dig trenches around the base of each tree
2) Hack at the roots with a combination of an axe, a bow saw and a hatchet (and some brute force)
3) Lever the tree, and repeat step 2 as and when necessary until the tree frees up, chop it up with the chainsaw
4) Once the tree was dragged across the garden, hack up the roots with an axe (and gusto)