A little while ago I was in St Pancras churchyard, where there is something called the Hardy ash tree. When Thomas Hardy, the novelist, was a young man he was employed to clear part of the churchyard to make way for the new railway. The gravestones were taken together and placed around the eponymous ash tree. The Internet has lot of photos such as these.
The effect is a poignant memorial to death, rather more affecting than most modern art I have seen. Of course, if the tree suffers from ash dieback, it will add another layer to the story.