Detect burning trees / burnt trees

[SilentStorm]

I was trying to detect burning trees / trees on fire / burnt down trees.
However it appears trees do not actually take any damage when they are on fire, and the only change that appears to happen is that the debug ui shows that the "progress" of the tree is advanced in increments of 1 to the final value 3 (or removed from the map).
However there does not appear to be an efficient way to be notified of trees burning or when trees arrive at state 3, nor does there appear to be a property for whatever value it is that the debug ui shows as progress.
I would rather not attempt to search all trees, especially since there does not seem to be a way to limit a search to burnt trees.
Only other way I can think of would be to constantly keep searching all the flames, and register for them being destroyed, which does seem somewhat excessive and not really all that UPS friendly.

Does anyone have any information on the 'progress' of trees or a different (more efficient) way of doing it?