This is TRUE! ...for 1000's of years societies have used this method to preserve WOOD! But... never "hardwoods" because they do not burn easily & when they do burn, it is harder to scrap/clear the char away. So they use "Soft Woods" like Douglas or White Fir!
Most people don't understand the concept or know they don't have to burn & scrap it anymore with propane "Torches"... all they need to do is "Scorch It"!
The concept reason is simple; Scorching Opens the Grains & Destroys anything that leads to DRY ROT!
Yes... Dry Rot is caused by bugs/etc that eat the deteriorating wood... even under the surface of paint or coatings w/ minute pinholes, where water leaks in!
So now the idea w/ these high heat Propane Torches is to Blast it w/ Torches...
enough to do what people have been doing for so long and not have to do more than Blacken it to raise the grain & penetrate into the wood to destroy anything that could lead to "Dry Rot" only! ...of course, creosote would do it for the part in the ground, but it's used primarily on things like Railroad Ties... etc to do the same thing! ...yet today "Propane Blowtorches" do it cheaper, easier and it doesn't take forever... to do like burning it!
Scorch to Get Color Change on Soft Woods like Cedar, Douglass or White Fir and it's cheaper & better than any other method!