we found someone have a tree chopped down in their garden (round the corner from us) the other day and asked the man chopping if instead of just getting rid of it which would have cost him whether we could have it instead, he promptly delivered a whole tree to us! It was chopped into big massive bits so my dh got the axe out and chopped it into lots of logs that are currently keeping me warm! Hard work (for dh!) but free!
Dead wood is often left in parks & woodland as a habitat for insects, to encourage birds. I don't suppose you've destroyed the entire eco-system of the park by removing one log, but it's not really a Good Thing to do.
My mate does this sort of stuff all the time, she heats her whole house all year for free! Last year she blagged our town xmas tree, accosted the men who were taking it down, got them to chop it up for her then she took it away.
southeastastra i know an hour later it was on our drive! we were chuffed! we live in the countryside so often keep an eye out for any of the tree felling chaps by us and ask them what they plan on doing with the tree theyre chopping down, we get loads of free trees its great! The one im burning now isnt seasoned but its burning lovely, lasts a bit longer as well! Have to give lots of credit to my dp though who gets out there and chops them all up and stacks them, he's fab! (even when poorly! yay my dp!)