i just discovered a few wooden planks nailed into a huge tree on some property i just bought in upstate new york. the planks, which i assume were once used as steps to the higher branches, are mostly rotted away and what remains are a few rusty nails jutting from the tree.

i have two questions:
1) what is the safest way (for the tree) to remove those nails?
2) if i ever wanted to attach anything new to a tree (steps for a treehouse, a birdhouse, clothesline, etc.) what is the best way (and safest for the trees) to go about that?

Interestingly enough, i also discovered some old, rusty barbed wire running through the property. some of it was attached to rotted posts, but some was attached to trees. some of the trees grew entirely around the wire, absorbing it into the trunk, while other trees where the wire passed through were nothing but stumps that appeared to be burned. my only (amateur) theory is that lightning traveled through the wire and burned out some of the trees. by why only some? there are so many things i need to learn about my new woods.

ideas?