Why do forests need fire?

By Sneha Das, C2ST Intern, University of Illinois Urbana-Champaign

The smoke from the Canadian wildfires blanketed the Chicago skyline in an intense haze a few weeks back. The news headlines, air quality warnings, and my time indoors on an otherwise beautiful summer day made me wonder, how much do I know about wildfires? The outcome – this blog!


Wildfires are out-of-control fires that burn natural landscapes like forests, brushlands, and prairies. Some natural causes are lightning, dry and hot climates, weather patterns like El Niño, and volcanic eruptions. However, 85% of wildfires result from human activities like campfires, careless disposal of burning cigarettes, or deliberate acts of arson. 

Imagine this scene, a hot and dry summer day with the bright sun shining down on the mountains covered with dense pine trees. There are dry pine needles on the forest floors and the rustling sound of leaves that blow in the wind. Seems delightful, doesn’t it? What I just described is the perfect setting for a wildfire! 

 The fire triangle – heat, fuel, and oxygen are the necessary ingredients for wildfires. In the above scenario, the sun is a perfect source of heat that can ignite a flame. The overgrown forest and its dry leaves on the forest floor are a perfect fuel for burning. To maintain this combustion reaction, only 16% oxygen content is necessary. With 21% oxygen in the atmosphere, there is an abundant and endless supply. Winds blowing uphill can transport the fire quickly, spreading at an average speed of 14 mph. Soon enough, the small flame can transform into a sizable fire and cause widespread devastation. The consequence of wildfire results in acres of vegetation burning, destroying surrounding towns and properties, and endangering people, wildlife, and livestock. This is not fiction but reality!

 Last year in the United States, 68,988 wildfires burned 7.6 million acres, an area about the size of Maryland. Decades of national policy deemed all fires destructive and have, therefore, suppressed them. This resulted in the massive and devastating wildfires we witness nowadays. While suppressing fires can be helpful to us in the short term, forest fires are beneficial in the long term.

Why do forests need fire? Let’s take the example of lodgepole pines. These coniferous trees commonly grow in the western part of North America, a region where wildfires are frequent. The seeds need a lot of sunlight and open space to germinate and grow. But the canopy formed by older and taller trees, some reaching a height of up to 75 feet, make it challenging for light to reach the forest floor and sprout the seeds. 

 To overcome this problem, lodgepole pines have two types of cones – the regular cones that release seeds annually and the resin-covered serotinous cones where the seeds survive for decades. High temperatures (around 50°C or 122°F) are necessary to melt the resin coating and free the seeds. 

 Forest fires release millions of seeds from serotinous cones. The fire also clears the canopy by burning down the older trees and removes any invasive plant species or disease-causing microorganisms. Low-intensity fires increase soil fertility as nutrients from dead plants can be used by new ones. After a forest fire, new lodgepole pine seeds germinate, grow, and thrive in a sunny and open area with nutrient-rich soil. 

 Just like lodgepole pines, other ‘pyrophytes’ like Giant sequoia and California redwoods are also adapted to fires. ‘Fire scars’ or burn marks on tree rings are evidence that forest ecosystems have evolved with fire for eras. 

 Years without fire have led to the decline of lupine plant habitat and endangered butterfly species like the mission blue butterfly and Karner blue butterfly. The caterpillars feed on lupine plants in their early life, and these plants need fire to flourish. The indigenous practice of ‘good fire’, today known as ‘controlled burning or ‘prescribed burning’, is being implemented to recover these butterfly populations. 

 Our ancestors viewed fire as an essential part of nature and because of naturally occurring fires, our forests have grown and thrived for centuries. The death of an old forest makes way for a new one, and for life to continue, forests need fire.


  1. https://apnews.com/article/canadian-wildfires-chicago-smoke-air-quality-aqi-e120fa48b44e6c8560b13712ba76ee1dhttps:/apnews.com/article/canadian-wildfires-chicago-smoke-air-quality-aqi-e120fa48b44e6c8560b13712ba76ee1d
  2. https://www.climate.gov/news-features/blogs/enso/how-might-el-ni%C3%B1o-affect-wildfires-california
  3. https://smokeybear.com/en/about-wildland-fire/fire-science/elements-of-fire#:~:text=Air%20contains%20about%2021%20percent,processes%20that%20occur%20during%20fire.
  4. https://science.howstuffworks.com/nature/natural-disasters/wildfire.htm
  5. https://www.nps.gov/places/000/lodgepole-pines.htm#:~:text=They%20can%20be%20up%20to,be%20killed%20by%20ground%20fires.

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