Wildfires used to be very helpful. How did they become so hellish?


When the first people arrived in North America, they used the benefits of small-scale, periodic fires to transfer their Make the ecosystem more productiveBut with the spread of Europeans and later housing and industry in the western states, the concept of fire fighting emerged: in order to protect lives and property, wildfires must be extinguished as soon as possible. In the dry forests of the western United States, there is not a lot of microbial activity to recycle vegetation, which leads to dangerous fuel accumulation.

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Consider the area around the town of Cranbrook in southeastern British Columbia. Before the fire was put out, its forests were mainly Ponderosa Pine and Douglas Fir, with less than 50 trees per hectare. On average, the area experiences relatively mild wildfires every seven years. Any low-intensity fire that burns through grass, shrubs, and litter will save most of the trees, while still controlling their numbers.

But due to fire fighting, there are now 10,000 trees per hectare, 95% of which are Douglas fir. There are no regular fires to regulate tree populations, and the species has taken over. “This is a classic example of how if you take the fire out of the system, you will have a truly significant change in species and structure-in this case, basically density,” Gray said. Since the trees are so dense now, the fire can spread between them more easily and throughout the landscape. To make matters worse, he said, the number of trees per hectare has now increased by 200 times. “This is unlikely to be a surface fire,” he continued, or a fire that mainly affects bushes. “This will be a high-intensity crown fire. It will kill everything.” In a canopy fire, flames spread between the treetops.

Due to the combination of high-density fuel and the lack of natural fire belts, the landscape loses its “herd immunity”. Now, wildfires can spread quickly because they have many new areas that can be “infected”. Plants and animals are less prepared for such large-scale fires. “The fire burns hotter, and the species living there may not adapt to this high temperature,” Gray said. “If a fire occurs in a large area, it will be difficult for them to re-invade a place.”

If the forest is destroyed, it will create problems that may last for several years.The surviving animals will have no cover Avoid predatorsThe resulting burns are also ripe for the colonization of invasive species, especially opportunistic weeds, whose seeds begin to blow in from the surrounding area. If they were established first, they would weed out any native species that also tried to return to the burn scars. “They did take advantage of these conditions,” Gray said. “And they can really change the ecology of the website by making it very simple, a kind of homogenization.”

So how do you know whether wildfires are “good” or “bad” for the landscape? Calculate trees through satellites, drones and airplanes. In low-level fires, less than 20% of trees will die. For high-intensity fires, more than 80%. The damage of a fire can vary greatly: the edges may burn more than the inside, and vice versa. Size is also a factor. “If the patch is large enough, basically the forest must be re-invaded from the edge,” Gray said. “If it is a fire of 50,000 hectares, rebuilding the forest is a long process.”

Wildfire ecologists also analyzed the soil structure and chemical composition to determine the intensity of the fire. For example, the presence of red iron oxide indicates that the wildfire is burning very hot. If scientists find that the root structure and buried seeds are alive well, it indicates that the fire is less serious.


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