100 years might be the limit of how long knowledge can last and still be useful enough though. 100 years is probably 6 generations.
Imagine explaining a complex process, like how to change the ink cartridge on a printer, via a chain of chinese whispers. Now put 20 years between each step of the chain, and remember all the intermediate people can't practice or try the skill they are described - they simply have to imagine it, since they have no fire to play with.
If the knowledge lasts that long, when a forest fire does happen, people only have one chance to figure out how to keep it alive. Accidentally put wet wood on it just once, and it's dead again for another 100 years.
Imagine explaining a complex process, like how to change the ink cartridge on a printer, via a chain of chinese whispers. Now put 20 years between each step of the chain, and remember all the intermediate people can't practice or try the skill they are described - they simply have to imagine it, since they have no fire to play with.
If the knowledge lasts that long, when a forest fire does happen, people only have one chance to figure out how to keep it alive. Accidentally put wet wood on it just once, and it's dead again for another 100 years.