timber preservation

when I was an apprentice many years ago. we were told that the best farm gate posts, were made of oak that had been burnt on the end that was set in the ground.The idea was an ancient form of timber preservation.what I was wondering was, is there anyone that could tell me if they have heard of this form of timber preservation or other methods of treating timber without chemicals.

Heard, yes. The technique goes back at least to the middle ages, probably longer. How to actually do it, besides charring a couple of mm of surface, don't know.