Ecology of Forest Fires

[Morganator 2.0]

It seems like every summer now there is a massive forest fire somewhere in North America. It always irks me a little that people think that the reason forest fires are becoming more frequent because of climate change. So I'm going to give a simplified explanation (that hopefully everyone, of all education levels will understand) to set the record straight. First, you need to understand two concepts; ecological succession, and the intermediate disturbance hypothesis.



After a fire burns through an area, the first thing to grow back are the grasses. Grass can quickly grow back, so they are the first thing to spring up. After a while, the grasses are overtaken by small shrubs. The shrubs can push the grasses out of the way to grow. But the shrubs are out-competed by bushes, which grow even bigger, and cover a larger area. The shade-intolerant trees come next (they need lots of sunlight to grow). They grow bigger than the bushes and block out the sun. The shade-intolerant trees get out-competed by the shade-tolerant trees, because they can grow in the shadows of the other trees, and eventually grow bigger, leading to a mature forest. The ideal forest right?

Nope, not at all.

You see, the mature forest keeps growing, and the trees keep competing for space, and one species eventually comes out on top. They conquer the entire forest area, creating a monoculture.



This is trouble for animal species, because many of them need a variety of plants, not just pine trees. Beavers use small aspen trees for dams. Deer and other ungulates eat from bushes and grasses.

There is this weird notion of a "Balance of Nature", that things must stay the same, and this is absolutely false. Nature is chaotic and ever-shifting. The world we know now is not the same one from 1000 years ago. New species diverge, and old species go extinct. Always changing, which leads to the next topic.

Intermediate Disturbance Hypothesis

A healthy ecosystem should have a large variety of species. This causes the system to be more resilient to disasters, and provides more natural resources to humans. So how do you get this? This hypothesis states that you need an intermediate number of disasters. Too few, and ecological succession leads to monocultures of one species. Too many disturbances, and you also get a monoculture. I couldn't find the exact quote, but one of the first expeditions that came back from the Canadian prairie had one of it's members comment "Oh my God, there are so many fucking fires." Because brush-fires are so frequent, the only thing that can grow back fast enough are grasses. What you want, is an intermediate number of disturbance; not so much that you only have grasses, but not so few that it's only trees. In this picture, you can see grasses, shrubs, bushes, trees, a wide variety of species. This is because fires don't come super often, and they aren't rare events. There are sections of this forest at different stages of succession. This is called a shifting mosaic.

Forest Fires

One thing very important. Tell everyone you know. Tell your parents, your friends, eco-warriors, and the kids at summer camp.

Smokey the Bear is a liar and a traitor.

This is the great irony. Forest fire prevention is what's causing these massive forest fires. Now I have your attention. Think about it; if you always stop a fire, then you're creating a situation with low disturbances. This causes the shade-tolerant trees (pines) to out-compete the entire forest. Pine trees have resin in them; it's very flammable. Also, the litter builds up. Pine needles and leaves build up at the base of trees. If you've ever lived on a farm with cows or horses you might be aware of this danger. It gets really hot underneath all that dead plant material, until it combusts. Spontaneously. And then your barn burns down. Or in this case, the barn, your house, and the entire forest around it. It's all pine trees and needles, so the fire gets out of control very quickly. It happens every year.



So the solution is now controlled prevention. Don't stop all the fires, just the ones that get close to people. In some places (mostly national parks) the park rangers and keepers need to start the fires. Firebreaks (pictured above) control how far the fires burn. With controlled fire management (instead of all-out fire prevention), the forest becomes a shifting mosaic with high species diversity, and much less flammable trees.

[Red_Wyrm]

I wanna assume you made this just for me

So forest fires are a part of nature, they are one disaster, or disturbance, as you put it, which keeps one species from dominating the ecosystem. This same concept can be applied elsewhere, right? Not just forests and forest fires. What about like the ocean and aquatic ecosystems. I don't think a fire is a very common type of disturbance there, but you would still need something to stop one species from taking over.

And the dominant species does not have to be a plant, does it? You mentioned:

The mature forest keeps growing, and the trees keep competing for space, and one species eventually comes out on top. They conquer the entire forest area, creating a monoculture.

I can't think of a reason why it wouldn't be a plant except when we are talking about ecosystems where there is no sunlight, and therefore no plant life, and in that case the same thing still happens, where there is a dominant species?

[Morganator 2.0]

Yes, so another example would be coral reefs.

There are two dominant groups of corals; massive corals (which includes brain corals) and branching corals. At night, the massive corals release these tentacle-like stingers that kill any other corals they touch, giving them space to grow. Branching corals, to counter this, grow up and out. Their branches reach farther than the tentacles and block out the sun, killing the massive corals. In this case, the branching corals are the competitively dominant species. What keeps them in check is the frequency of tropical storms. When a powerful tropical storm comes by, the heavy waves knock over the branching corals, but the massive corals are fine. So in this case, the tropical storms are the disturbance.

It's also not necessarily a disturbance that can keep the competitively dominant species in check. Barnacles, anemones, and mussels all compete for places to attach themselves to substrate. Mussels are the competitive dominant species because they produce way more offspring, so their spores are most likely to attach to vacant substrate. What keeps them in check are starfish. The starfish hunt mussels, which continuously frees up space for other species to grow. This also creates that shifting mosaic.

[Red_Wyrm]

The starfish hunt mussels.

This is the single coolest thing I have ever read.

So it kind of seems like a predator/prey differential model. You have the wolf population which eats rabbits until the rabbit population is really small. Then, because of the lack of rabbits, the wolf population decreases. because the wolf population has decreased, the rabbit population increases. Now that the rabbit population has increased, there is more food for the wolves and the wolf population increases, and it oscillates like that.

Except it also doesn't seem like that at the same time. Maybe it is just a more complicated version of the basic introductory model I've learned about?

I am now legitimately afraid of star fish, as if they are going to hunt me. Thanks for that. Every time I see one on discovery channel I am going to imagine being eaten by it, attaching itself to the top of my head and slowly sucking my life juices out of me. I'm not sure how starfishes work, so this is what I imagine. Thank you, sir/ma'am.

I still don't know.

[Red_Wyrm]

Hey so the Amazon is burning right now, and I was like okay kewl. Morgy told me its natural. Then I saw an article, which I didn't read because I am morally opposed to that news company (not for political reasons), and the headline was something along the lines of "Leaked Document Reveals President of Brazil Wants the Amazon to Burn"

So I was curious to your thoughts Mr./Mrs. Forest Fires Expert of Deckstats, what are your thoughts on the topic?