What I did in this map was get in a car and run over some things, then I died and was presented with the following "game finished" screen:
There are several peculiarities here:
- Aside from biters, all things are inanimate objects, and as we all know, one "can't really kill" them.
- In terms of trees there's way TMI - IMHO, trees should be grouped into just one item - Trees. I guess a similar thing would happen for rocks etc. I understand that this may be useful for development purposes, but for players it's pretty meaningless.
- As for landmines - these are things that "kill themselves" when triggered by biters, so it's not really correct to count them as player kills (unless they belong to some enemy team and were destroyed using grenades or something of that sort).