Wildfires Used to Help. How Did They Do So Bad?


When the first people of North America arrived, they took advantage of the small, everyday fires by setting their own the ecosystem is more productive. But to Europeans, and after the spread of housing and industry in the western states, came the concept of fire prevention: To protect life and property, fires must be extinguished as soon as possible. In the arid forests of the American West, where there is not much microbial activity to recycle plants, this carries the risk of fuel accumulation.

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Consider the area around the town of Cranbrook in southeastern British Columbia. Before the fire was contained, its forests were mostly focused on pineosa and Douglas fir, which are probably less than 50 trees per hectare. The region will experience a relatively light fire every seven years on average. Any fire that has a high intensity of fire through grass, plants, and timber waste can avoid most of the trees, while continuing to secure their population.

But as a result of fire suppression, there are already 10,000 trees per hectare, 95 percent of which are Douglas firs. When there was no regular fire to control tree populations, the species took over. “That’s a classic example of how you get out of the system, you get a significant change in species and in structure-in fact, a lot of it in this case,” Gray said. Due to the tree trunks being very clustered, fires can easily spread between them and march into a scene. Even worse, he says, with 200 times the number of trees per acre now, “it can’t be a fire on the surface,” he continues, or one that has largely affected the underbrush. “It’s going to be a huge fire in the crown, and it’s going to kill everyone.” In a crown fire, the flames spread between the peaks.

Due to this combination of dense fuels and lack of natural firebreaks, the scene of “host strength” was lost. Today, fires spread quickly because they have many new areas that they can “cover.” And both plants and animals are less prepared against this different fire. “The fire burned much hotter, and the species that lived there probably didn’t adapt to the heat level,” Gray said. “And if the fires happen in a large area, it’s much harder for them to invite a venue as well.”

If a forest is damaged, it creates problems that can last for years. The animals that survived were uncovered hiding from predators. The resulting burning is also ripe for the colonization of invasive species, especially the exploitative weeds, whose seeds begin to blow from neighboring areas. If they are first established, they will relocate any native species that are also trying to get back the burn scar. “They really take advantage of those conditions,” Gray said. “And they can really shift the ecology of a site by making it simple, a kind of homogenized.”

So how do you know if a wildfire is “good” or “bad” for a scene? By counting trees via satellites, drones, and planes. In a short fire, at least 20 percent of the trees will die. For a severe fire, it’s more than 80 percent. The level of damage can vary slightly inside a fire: The edges can burn above the inside, or vice versa. Size is also a factor. “If the patch is just right enough, basically the forest has to grow from the edges as well,” Gray said. “If it’s a 50,000-acre fire, that’s a long process to rebuild a forest.”

Wildfire ecologists also examine soil structure and chemistry to determine how severe the fire is. For example, the presence of a red iron oxide, indicates that the fire is very hot. If scientists know that root structures and buried seeds survive just as well, that’s a sign of less severe fire.



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