Day 13.229: "Refuses to die"

There were a number of signs on the first trail we walked at Massabesic Experimental Forest back on Day 13.221. Many of them had numbers or letters - presumably for some kind of educational tour. Most of the rest had the names of species of trees, but there were a few oddballs. This was the oddest:

And what was the sign referring to? Not easy to see at a first glance:

But that fallen down tree - as the sign says...seems to be refusing to die (see top left here):