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Comment by xyzzyz | Hacker News Reader

If only conditions matter, but triggers do not, why don’t all forests catch fire all at the same time when it gets dry enough? Think about it: average forest in California will probably get dry enough to support forest fire at least every few years. Why then it takes decades or centuries until the fire actually visits them?

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Triggers are necessary for fires, obviously, but getting rid of the triggers does not solve the problem. There's another wrinkle to the whole matter: when a forest survives the dry season without burning down it doesn't reset. The following year there will be even more dead wood and other dry material in the area. This means next year's potential fire will be even worse than the last.

One step at a time. Forest management is a huge issue. Wildland firefighters are zealous, almost paramilitary organizations that try to vanquish every fire like enemy invaders. In reality, fires are part of the lifecycle of forests that clear brush and make the forest healthier and more resilient in the future.

At least nowadays wildland firefighters spend plenty of time conducting prescribed burns, too. They're not chuckleheads - they're perfectly well-aware by now that past practices contributed to the problem.

But they are hired by and paid by politicians who know smokey the bear and don't care at all about the modern science of forests. Not to mention courts regularly block their attempts to control the forest (ironically often by lawsuits brought on by environmental organizations) As such they often are not allowed to do the right thing for the forest even though they know what to do.

>In reality, fires are part of the lifecycle of forests

Let's be absolutely clear that this is only true for a limited number of forests. The evidence for this is the existence of very old trees.

Unfortunately many forests will become increasingly susceptible to fire as dry seasons are extending in many areas due to climate change.

> The evidence for this is the existence of very old trees.

Lots of tree species are able to survive a forest fire once they reach a certain size. There absolutely are very old trees in areas that burn frequently.

"Very old trees" generally means fire-resistant old trees, and frequent but mild fires regularly affecting the less-flame-resistant undergrowth.

There is a limit on how much dry wood a forest can accumulate. At some point old dead wood will rot and become soil. Though in dry climate rotting is slow.

That is interesting. I thought rain reset the conditions.

Rain can make it worse by adding more growth that then dries out and becomes fuel.

https://en.wikipedia.org/wiki/Fire_triangle: “a fire needs to ignite: heat, fuel, and an oxidizing agent (usually oxygen)”

There also always is plenty of oxygen. In dry summers, there’s also plenty of fuel. What’s lacking is sufficient heat. The ignition temperature of wood is difficult to assess, but wood can start burning at 125°C ≈ 256°F (https://www.warrenforensics.com/wp-content/uploads/2016/06/P...)

It doesn’t get that hot without help, e.g. from a campfire, a magnifying glass, or sparks from electricity.

Or lightning. Lightning can and does happen without rain, too.

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