In oups.com
wrote:

She has been told that she needs to get rid of the trees and that there
is a "special something" that needs to be applied on the cut trunk
...or something...

After it's been cut down, the "special something" that needs to be
applied to the tree trunk is called a "stump grinder".

Each year, I watch the city cut down dozens of Elm trees as Dutch Elm
Disease continues to eat away at them, and after they're cut down they
grind the stump into dust and haul it way. A little fill, a little sod and
after a while, there's no sign the tree was ever there.

In your case, you'll probably have to do something to get the sidewalk
leveled up.

--
Bert Hyman St. Paul, MN