1. No. Some people SWORE that they could keep a resource square from changing my only hitting it "x" number of times, but the devs said it was just the act of hitting the source ONCE for that resource, that triggered the change possibility. Eventually, this was proven correct, as trees changed that were only beeing hit for 50-60 logs per trip.
2. Can't speak for the trees, but for mining, there are no areas that are always only Iron. Should be the same for trees, barring some accident of coding. Do note, that the ratio of colored/normal wood, and number of productive swings for that square, stay constant, regardless of the resource it currently is, so as long as you can get that spot to produce X% of colored resource for you on average, it will do it whenever that spot produces ANY colored type of that resource. The only things that affect this are racial bonuses (which themselves are debatable for smithing, but obviously a big factor in lumberjacking) and the actual availability at the moment of a colored resource (which for mining, is simply a matter of using special tools).
Dangit, I want a forester's tool to elevate woods!
