I think chopping trees down with an axe is way too easy. It should take far longer, as should sawing, with a progress bar so you can continue on from where you left off if you need to interrupt it. This would make dismantling objects like doors/wardrobes for planks/wood be far more necessary (and how many times do people in a zombie movie chop down trees? They're always breaking up furniture tho.)
And when chainsaws are in, it'll be a nice balancing act between noise/fuel and the extra time it would take to just use an axe.
Also, making chopping/sawing harder would essentially make them be two separate jobs (as in, one player helping another out by sawing what they chop) for players in multiplayer/eventual NPCs, helping with roleplaying etc.
