After using the spade on the willows trees stump that is left behind located at the falador mud patch, the tree stump can still be seen. (Not only falador mud patch, there is 1 located at rimmington had the same issue)

I try a ::reloadmap command, it didn't make the tree stump disappear, however a relog fixes this issue.

The only way to make sure the tree stump is gone is to plant a new tree on the mud patch.