An epitaph is what goes on a gravestone in memory of whomever the gravestone is for. It may be a poem, a sentence, or just a few words.

A brief sampling of ideas:

Dead Eucalyptus, we mourn for thee!

A tree is absent here,
killed on a whim.

My dear old tree, where are you now?

Hey, look! No tree! No wonder our air quality is so bad...

Gone without a trace,
Maybe my tree was a mirage.

My lungs cry for the future generations.

Oak--
'Bye.

Here rest the remains
Of an old cherry tree. Mourn,
For it blooms nevermore.

Timbeeeeer!

Another casualty of commercial expansion. *Sigh*

What happened to my tree?