Fire has been a major force in the evolution of land-based life. Even more so in the distant past. In the Cretaceous (70 - 140 million years ago) both temperatures and the oxygen ratio in the atmosphere appear to have been higher than now. The whole planet was covered in a thick tropical forest -- and it burned easily. The dinosaurs had to contend with continent-wide forest fires, and their bones are often found in the middle of a layer of charcoal.

Absolutely, many trees have evolutionary countermeasures to fires. Some trees are very well-suited to colonized disturbed ground - they will opportunistically surge into an area after a wildfire, as either more of their seeds will germinate, or more seedlings will sprout into favorable conditions. Other trees have adaptations that make it more likely to survive wildfire; both sequoia and douglas-fir have layers of insulating bark up to a foot thick.

Some trees have adaptations to ensure that their seeds only spread after a wildfire; sequoia cones are sealed shut by a resin that only melts in the intense heat of a wildfire. Some species can even be thought of as having adaptations that encourage wildfires in order to out-compete species that are less wildfire-resistant; grasslands require wildfire on the shoulders of foothills, where otherwise trees would gradually creep down the slopes. The dry foliage at the end of summer provides ideal conditions for wildfires.

If you want to learn more about fire adaptation, an excellent entry point is https://en.wikipedia.org/wiki/Serotiny.

If a tree lives on average for 200 years, and has a mortality rate of 100% in a forest fire, you don't need fires to be very common for adaptations to fire to be worth it. Just one fire in each forest every 2,000 years or so would be enough. 20,000 years should do too, but I'm less confident of this.

Was lighting more common? Probably not. Were forests bigger and less gardened to prevent spread of fire? Definitely. So for each tree, there was a much larger area of vulnerability to lightning strikes.

> Were forests bigger and less gardened to prevent spread of fire? Definitely. So for each tree, there was a much larger area of vulnerability to lightning strikes.

May be. We can't be sure about that.

Those forests housed a lot of megafauna. I can easily imagine American mammooths "gardening" the forest and removing everything green and edible from the soil. Giant slots, giant rhinos like Paraceratherium, Giant marsupials like Diprotodon, elephants and other mega herbivores most probably roamed searching the huge bulk of plant products that they needed each day. They most probable needed to complete its diet with suboptimal food like fallen leaves, barks, branches and dry weeds to reach its quota.

Most of that megafauna went extinct by men and that can't be fixed. Of those that survived, the 60% of the extant big herbivores are in danger of going extinct now, so the problem could take a big turn for worse.

European bison was a candidate to reintroduction for the possible benefit of cleaning branches, thorn shrubs and flammable materials from forests soils that cattle don't touch.

This is certainly true for the American West. Unfortunately in places like Patagonia the lenga trees never had to adapt to natural fire, so man-made fires are catastrophic.

In areas prone to fire some plants do have evolutionary adaptation.

In the Mediterranean, cork oaks have thick bark (which we use to make cork for wine bottles...) that scorches while the tree survives.

The seeds of Australian acacias need the heat from wildfires in order to germinate.

In some cycads the heat of fire triggers blooming, and gardeners stick hay in the crown and set it on fire in order to get a bloom and seeds.

Etc.

Maybe. But most fires in the California coast are human caused. Today, lightning is extremely rare.

Furthermore, be careful extending this train of thought to other biomes. My understanding of California chaparral is it's evolved to survive fire, but if it happens too often the biome disappears and turns into grassland. Some of the plants take decades of recovery before they are capable of fruiting.

Just because a species has evolved to survive fire doesn't necessarily mean it needs it.

> But most fires in the California coast are human caused. Today, lightning is extremely rare.

Is it actually any less common than it used to be, or are lightning fires simply a much smaller percentage of burning measured by fire count or acreage?

I can't speak for CA but up in Oregon we regularly have lightning causing fires all summer.

Massive fire suppression is uniquely human.

> But most fires in the California coast are human caused.

Worth a note that regular usage of fire to clear underbrush was a very, very long standing practice among the native population - long enough to have affected the landscape and the trees in it.

My understanding is that fires in forests are not only quite common and have been long before humans were around, but that naturally-occurring fires are a critical part of forest's natural lifecycle and evolution.

Yes. Some species actually need fire for their seeds to activate at all. I'm surprised this isn't more widely known. I wonder what would change about climate activism and wildfire management if more people understood this.

Yes, they do the bark of a redwood trees is fire resistance, and even certain seeds in the forest need fire in order to start their germination.

Trees native to many areas have developed evolutionary countermeasures to fires. Trees native to many other areas haven't. Some trees have measures to recover from being eaten or destroyed by large animals, and often those measures work equally well if the tree was damaged by fire or even burned down completely.

Trees are such a diverse group of plants that it's hard to say anything about them in aggregate

Some species of tree have cones that need to be burned before they will open. So, probably yes.

I can’t tell if this is sarcasm or not. But the answer to the first question has been known in the forestry community to be yes for quite some time.

For instance - there are certain species that require the heat of a fire for their seeds to explode and grow new plants.

It's not that the forestry community is petty, it's more likely that the HN community doesn't like comments that don't add substantively to the conversation, and particularly doesn't like them as an add-on to a thoughtful and polite answer to a question.

Doubting my integrity by suggesting I'm being sarcastic just because I don't know something that clearly isn't common knowledge is thoughtful and polite?

That describes me. Don't take downvotes as a remark on your position. I pass them out to anything that doesn't raise the level of discussion.

I also hand them out to every top ancestor comment that uses the word 'downvote', for the same reason.

I think the reason for downvotes here is that you don’t need to be in the forestry community to know this. It’s been in science textbooks since I was in 4th grade, kids did presentations and posters on it, it’s in documentaries, it’s on informational plaques in multiple national parks. The fact that some tree species are evolved to survive fires or require fires for germination is not controversial.

In California over the last few years, salience has led forestry and fire's place in it to become a bit less of a niche interest, at least certainly among the geekier/hn-leaning community.

Even places like New Jersey have done prescribed burns for the last 100 years (source: ex-resident))

ecosystems of trees differ greatly across the globe. Here in California, one widely cited reference article on this topic is doi:10.1093/biosci/bix146

Drought, Tree Mortality, and Wildfire in Forests Adapted to Frequent Fire Stephens, et al. 2018