Many wildfires start with the help of a human hand (a still burning cigarette was thrown away, campfires, fireworks, etc.). Only a small percent of them are ignited in one of the natural ways (strike of a lightning, volcanic eruption etc.). Fire can also start because of natural processes. If we look at the pile of organic matter, we can find many types of microbes and fungi. They are just doing their thing (decomposition*) and with this, they can raise the temperature in the pile up to 160 °C! The ignition can occur, if there is no mixing of the organic matter or if there is too little water. Another option (that is still theoretical) to start a fire includes a bit of water. If a drop is caught by hairy structures on a dry leaf, the drop can serve as a magnifying glass and can, potentially, start a fire.
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Decomposition is a process that they perform (together with other soil organisms) and it breaks the organic matter into basic nutrients, which are then used by plants.
A fire needs fuel, oxygen, and heat to continue burning and it only stops if one of the three components is not available anymore. The best fuel types are dry leaves, twigs and branches and the best conditions for spreading is dried up land, preheated by the sun with a bit of a breeze. In this way, the material has the highest possibility to get ignited and the wind helps to deliver oxygen and to spread the fire. When we try to fight the wildfires, we mostly try to redirect them or remove the fuel it could potentially reach.
There are three types of forest fires:
- Ground fire burns the organic matter in the soil and right above it. With this type of fire, only the roots, nutrient supplies and organisms living in the soil are affected.
- A crown fire is a type of wildfire we fear the most. When it occurs, the top layers of trees and shrubs are burning and since it uses a lot of fuel to keep going, they are very hard to put out.
- Surface fire burns through the dead plant matter that is lying on the ground (leaves, fallen branches etc). These fires often pass very quickly and don’t cause too much damage to the ecosystem.
In the ecosystems, we most often come across a mixture of all three types of fire, since all of the components are deeply connected.
During the fire, there are many lives lost and the species and habitat diversity has greatly decreased. There are large amounts of carbon lost from the ground and released into the atmosphere. The scientists have learned, that the carbon levels (and levels of some other elements) go back to the same levels as they were before the fire in only two years. This means, that the consequences of fire are not so devastating for the environment after all and can actually help increasing ecosystem health. However, when a severe wildfire occurs it should be followed by a longer, fire-free period in which the plants can mature and produce new seeds.
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As we all know, plants can’t really run away when a fire occurs. This is why they adapted themselves to survive in harsh conditions. Actually, for some plants, a wildfire is like a big new year’s eve party for us!
As I mentioned before, there are many animals that fleed and many that couldn’t escape the fire. But there are also some, that really like the smell of it. I am talking about some insect species (around 40) and birds of prey, that know that the feast is coming after the fire. There are also some amphibian and reptile species, that hide (burry themselves or use burrows of other animals) and wait for the fire to pass.
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How do plants respond to wildfires?
The organic matter that had burned away is now present in the ashes and still provides the needed nutrients. Since the organic matter that covered the soil is now gone, more sunlight and water is available for the seeds. There are also fewer microbes and therefore lower chance of spreading parasites or diseases. So actually, this is a real, broad paradise!
The life at a newly burned place doesn’t only begin from the seeds. The seeds are just leftovers of plants, that are intolerant to fire but their seeds are. We have two other groups of plants that we divide into fire-tolerant and fire-resistant plants. The first ones can withstand a degree of burning and can grow further even if they are damaged by fire. The other ones suffer little damage when they burn (mostly because their flammable parts are above the fire). To get a better overview of what I’m saying, here are some examples:
- The Banksia group is very diverse and the plants in it have different methods to survive the wildfires. Some of the species have seeds, that are stimulated to open and germinate when they have been through the fire. Some other species can continue to grow because of their special features, hidden under the bark. These special features are buds, that start to grow after such an event.
- Eucalyptus trees are in a family, that really, really likes to burn. They do everything in their power to enable the fire to spread. First of all, they have very highly flammable oils present on their leaves and secondly, they produce phenolics. Phenolics are stored in the leaves and prevent fungi to start the decomposition process. In this way, the organic matter is piling up and when the fire finally starts, they just can’t seem to stop burning. Why do they like to burn so much? It’s all about reproduction. Their seeds are safely saved in cones and are released only after the cone itself has melted away. The eucalyptus trees are fire tolerant when they grow in forests (and you can see how a burnt eucalyptus forest looks like here). Their surviving technique is the specialized buds under the bark, that start growing after the fire is over.
- How can a plant be fire resistant? There are two methods for this. The first one is to have a bark so thick, that it is impossible for a fire to penetrate it. The bark on this tree also acts as a thermal insulator, preventing any damage done to the tree itself. Of course, I am talking about a mature giant sequoia. On the other hand, their height also makes them fire-resistant, since the tree crowns are almost impossible to reach as they lack lower positioned branches.
Some of the mentioned examples also indicate the keystone species and ecosystem engineers. These species are very important to maintain since they are the ones who are keeping the ecosystems healthy.
After a wildfire, the battle for empty niches starts right away. There are many plant species, that can start the germination process and start to grow in a week. There are also many animals, that migrate here because there is a lot of food (dead animals, newly sprouting plants) and empty ecological niches.
I hope I gave you a good overview of the importance of occasional wildfires in nature. Fighting them off is not an option, because sooner or later, one way or another, they will start. It also needs to be taken into account, that the longer the wildfires were delayed, the bigger and more devastating they are going to be.