Question: In my world, I'd like to place a region of permanent forest fire, but I'm having trouble coming up with the minute details of the biome.

For example, my first idea was that it started when a lush, humid forest was exposed to a volcanic eruption, followed by a permanent but slow lava flow, lasting long enough that some plants have adapted and evolved into flora that relies on the constant fire and is itself so slow to burn it can outgrow whatever is lost to the fire.But how plausible is that, biologically speaking?

What is a better approach to creating a permanently burning forest?

Answer: 
Yes there is a better approach
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Gas pockets feeding the fire...

[![https://en.wikipedia.org/wiki/Darvaza_gas_crater#/media/File:Darvasa_gas_crater_panorama.jpg](https://i.stack.imgur.com/rGdcw.jpg)](https://i.stack.imgur.com/rGdcw.jpg)

...or underground coal seam fires.

[![https://www.globalforestwatch.org/blog/fires/embers-under-the-earth-the-surprising-world-of-coal-seam-fires/](https://i.stack.imgur.com/wjT6B.jpg)](https://i.stack.imgur.com/wjT6B.jpg)

The volcano essentially did a naturally occurring version of [fracking](https://en.wikipedia.org/wiki/Hydraulic_fracturing), creating channels to the surface for gas, while land slides exposed coal seams, in some instances laying the coal bare on the surface.

These fires ebb and flow with the seasons, especially effective if they are not the four seasons we have on the temperate parts of the Earth (Winter, Spring, Summer, Fall) but instead Wet and Dry seasons like in the tropics.

The biology would have to...

1. Grow fast
2. Spread Effectively
3. Survive Scorching

Vines and brush — where the roots go deep — would work, the plants survive having the surface parts scorched off because when the water comes, the roots shoot and grow new surface parts and send vines in all directions.

[![https://tallcloverfarm.com/3547/brambles-gone-wild-how-to-remove-blackberries](https://i.stack.imgur.com/H56Gi.jpg)](https://i.stack.imgur.com/H56Gi.jpg)

*Blackberries are infamous for forming [brambles](https://en.wikipedia.org/wiki/Bramble) and spreading quickly*

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So, to summarize:

* The fires are fed by subsurface sources, like gas and coal, not by "new" biomass
* The biology does not so much "adapt" to the fires as it is just very good at spreading and "ignoring" the fires by hiding underground.
Quite a few plants - mostly trees - have evolved to [require fire to germinate](https://www.britannica.com/list/5-amazing-adaptations-of-pyrophytic-plants)! This seems like the seed of what you might need - combined with a geography that's appropriate.

Annual fires are common in several areas; but what makes them not permanent is the weather cycles. This could possibly change, though, and become permanent in a way - if your geography allows the fire to "travel".

Imagine a Pangea type world, a single large continent taking up 30% of the surface area of the globe, say. If that Pangaea is ringed by forest, and if the weather patterns comply, it's possible that you could have a *travelling fire*, which, say, is on the east from March to June, the north from June to September (northern summer), the west from September to December, and the south from December to March (southern summer). (West/East could easily switch, of course.)

The fire could literally travel in that way, ringing the globe every year. Then, cultures would possibly come up that would worship the "renewing fire", have rituals based on it, etc.

I'm not sure what you'd need for the weather to work out this way (you'd need the rainy season to not coincide with the fire, but to coincide with the *end* of the fire, for example), so that part might be a bit handwavy - but it seems like a possibility, if you're not going into meteological science fiction, at least!