Are All Forest Fires Bad?

Every year we hear of forest fires that engulf cities, endanger human lives, and cause the mass destruction of property. These fires rage uncontrolled, so large that they cannot be put out, turning the skies red and charring everything in their paths. Forestry and fire services take many precautions to avoid these blazes. People visiting forests are told to be careful with their use of fire, with some national parks banning the lighting of fires altogether. In addition to this, large areas of forest are often cleared to prevent future fires from spreading. Water bombers—special planes used for dropping water on active fires—are kept ready to respond at a moment’s notice. Fires are seen by most as a menace—a danger to forests and people alike. But are forest fires really as bad as we think they are?

A water bomber suppressing a wildfire
A water bomber suppressing a wildfire, Credit: pxhere.com

Fires have increased in frequency, with the United States witnessing a threefold increase in the last two decades alone! Human activity, both intentional and accidental, has made ignitions in “forested” areas far more common. Nearly 85% of wildfires from 2000-2017 in the U.S. were anthropogenic (caused by humans). Owing to climate change, as well as the ways we use land, fires have also been increasing in size and intensity. Extreme fires now occur a lot more often than they once did.

 

Emitting a large quantity of greenhouse gases, causing considerable air pollution and billions of dollars in damages to property, it would seem that wildfires cause more harm than good. Why else would we spend so much time and money trying to stop them?

 

But is there more to the story? To answer this question, we have to don our evolution-lenses to take a closer peek at wildfires and the places where they burn.

Fires, Regimes and Ecosystems

Wildfires have been around since plants have been on land. Fossil evidence of fires—called fusain—has been found from the Devonian, more than 400 million years ago. Land plants and fires have coexisted for a long, long time, long enough for plants to evolve to cope with periodic burning, and even use wildfires to their benefit.

 

Wildfires in different places burn differently. Some regions burn intensely but infrequently, or might even have fires that burn below the ground. Other regions might encounter milder wildfires more frequently. Yet others might have fires that burn all the way up to the canopies of tall trees. Factors like the frequency, intensity, and location (above or below ground), and the plants that get burnt, change the ways in which fires burn. These factors, along with the way fires burn, are that region’s fire regime. Think of a fire regime as a specialized way of life for the plants of a region, one that depends on the occurrence of fires in a specific way.

 

Thus, plants have learned how to live with wildfires, and often can dictate the way in which fires burn. Fires, in turn, make plants adapt to their presence, and modify the ecosystem. This means that fire regimes are controlled by complex relationships between plants and fire.

 

An example of this dynamic are the longleaf pines found in the Southeastern USA. In the 1920s, a forester named H. H. Chapman theorised that longleaf pines require periodic fires to survive. These pines are outcompeted by other hardwood species found in the area, and commonly suffer from a disease caused by a fungus. Longleaf pines have a hard time establishing themselves in forests amongst other plants. They grow rapidly to the height of a few inches, and then sprout a ring of fire-resistant pine needles. They then stop growing for a few years, sending a large network of roots underground, waiting for the opportune moment. When a fire strikes the forest, the competing plants burn. Pine needles suffering from the fungal disease also get burnt off. The longleaf pine jumps into action, rapidly reaching for the skies. It soon grows big enough to withstand any but the largest of fires. Some pines even retain their dead branches to act as fuel for fires, using their higher flammability to kill their competing neighbors.

 

Serotiny is a phenomenon where plants such as the sequoia, cypress and eucalyptus delay the dropping of their seeds until the passage of a wildfire through their surroundings. Upon the arrival of a fire,  the adhesive wax holding the seeds within melts, causing the trees to release seeds from their canopies. Serotiny effectively protects the seeds from the ravages of the fire and other hazards present on the forest floor, and presents them with an ashy, nutrient rich medium for germination once they drop.

 

Other plants, such as Terminalia elliptica, the crocodile-bark tree, so called for its likeness to the scales of a croc, have thick, spongy barks. These barks, acting like fireproof jackets worn by firefighters protect the rest of the tree inside from temperatures nearing 800 degrees celsius! (over 1400 degrees fahrenheit!)

A longleaf pine with its ring of needles, waiting for a fire
A longleaf pine with its ring of needles, waiting for a fire, Credit: Wikimedia/Joseph O'Brien, USDA Forest Service

Many grasslands and savannas around the globe depend on fires for their existence. The climates and soils that host these grasslands would also support woody plants. Furthermore, woody plants prevent grasses from growing by taking all the sunlight and leaving grasses in shade. Why, then, do these areas host grasslands instead of forests? Fire!

The fire regimes of a savanna
Credit: Wikimedia/ETF89
forest
Credit: theacademyadvocate.com/Noah Berger

The fire regimes of a savanna (left) are very different from that of a forest (right)

Grasses are used to regimes where there are regular, large burns. They grow during the rainy season, building up large amounts of fuel, and then dry rapidly as the weather gets warmer, providing the perfect conditions for wildfires to run free across the surface of the ground. A majority of the biomass of grasses, however, is stored underground, safe from being scorched in the infernos to come.

 

Saplings of woody plants, however, don’t do very well in these frequent fires. Unable to grow significant amounts in the short time they have between burns, these saplings cannot escape the fire trapthe height above ground encompassed by the flames of these grass-fuelled fires. Saplings of woody plants thus get killed in the blaze. Woody tree species only stand a chance in these landscapes when there are periods when fires are delayedwhen the saplings that survive manage to grow taller than the fire trap. This limits the number of woody plants, and so forests are stopped from invading the grasses’ turf (pun intended).

Humans, flora and flames: Where to burn, when to burn

There’s just one big problem that fire-controlled environments face. For centuries, many forest-dwelling communities of people used wildfires as a tool to manage forests. The fires they set ablaze largely mimicked the fire regimes of natural ecosystems. Slash and burn or swidden agriculture, for example, involved the careful choosing and burning of a patch of land. The burning cleared the land for agriculture. Crops were then grown in these patches for a few years and abandoned afterwards. The clearings left in the forest were soon reclaimed by nature, until the farmers returned. This repeating cycle allowed nutrients to return to the soil. More importantly, it gave saplings the chance to grow in unobstructed sunlight, helping the next generation of plants.

 

Controlled burns were also used to reduce the intensity of fires. Using up accumulated fuel on a regular schedule pre-empted the occurrence of extreme burns. These prescribed burns are still used by many forest services for the same reason

Fighting fire with fire: Prescribed burns are controlled fires that are set intentionally to stop larger fires
Fighting fire with fire: Prescribed burns are controlled fires that are set intentionally to stop larger fires, Credit: maxpixel.net

But now, climate change and human activity are altering fire regimes across the planet. Large patches of forest are being lost to extreme fires, turning them into scrub jungle and grasslands. Meanwhile, grasslands that are prevented from burning are being taken over by woody species, and converted into forests. Such biome switches are not easily undone, and lead to the loss of many species.

 

From fires in the Amazon rainforest, to bushfires in Australia, wildfires have gone from being a force of life to one of extermination. Fire, like many other things, is best in moderation. And the laws of nature and evolution know just the right amount for the right places. Perhaps this is a strange case where, to save the world’s wilderness, one has to first let it burn (the way it should).

Glossary

Anthropogenic: Arising from the activity of humans

 

Fusain: Bits of charcoal that have been fossilized

 

Fire regime: The pattern, frequency, intensity, and nature of the fire burning in a particular ecosystem

 

Biomass: The amount of organic material that comes from plants or animals

 

Fire trap: (In this context) The zone (height off the ground) that would be within the flames of a fire

 

Prescribed burns: Wildfires that are intentionally lit to reduce the risk of larger, uncontrolled fires

 

Scrub jungle: Ecosystems dominated by shrubs and herbs, as opposed to forests that have taller trees

Flesch Kincaid Reading Grade: 8.2

 

Flesch Kincaid Reading Ease: 64.2

The ecology of fire, Nature Scitable

https://www.nature.com/scitable/knowledge/library/the-ecology-of-fire-13259892/

 

The ecology of Fire, C.F. Cooper

https://www.jstor.org/stable/24937430?oauth_data=eyJlbWFpbCI6InByYWR5dW1uYS5yYWphc2hla2FyQGdtYWlsLmNvbSIsImluc3RpdHV0aW9uSWRzIjpbXX0

 

Fire Effects on the Environment, USFS Pacific Northwest Research Station

https://www.fs.usda.gov/pnw/page/fire-effects-environment

 

The Impact of Forest Fire on Forest Biodiversity in the Indian Himalayas (Uttaranchal), Amit Parasher, Sas Biswas

https://www.fao.org/3/XII/0358-B1.htm

 

Fire as a global ‘herbivore’: the ecology and evolution of flammable ecosystems

https://www.sciencedirect.com/science/article/abs/pii/S0169534705001321

 

Wildfire Causes and Evaluations

https://www.nps.gov/articles/wildfire-causes-and-evaluation.htm

 

How Much Do Wildfires Cost in Terms of Property Damage?

https://www.scientificamerican.com/article/graphic-science-how-much-do-fires-cost-property-damage/

 

The ecological sustainability of slash-and-burn agriculture

https://www.sciencedirect.com/science/article/pii/016788099400531Ihttps://www.sciencedirect.com/science/article/pii/016788099400531I

 

Wildfire Causes and Evaluations

https://www.nps.gov/articles/wildfire-causes-and-evaluation.htmhttps://www.nps.gov/articles/wildfire-causes-and-evaluation.htm

 

U.S. Fires Quadrupled in Size, Tripled in Frequency in 20 Years

https://eos.org/articles/u-s-fires-quadrupled-in-size-tripled-in-frequency-in-20-years

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Author

  • Pradyumna Rajashekar

    Pradyumna is a Biology undergraduate, with a taste for Ecology and Wildlife Biology. He has an appetite for understanding biological systems, and sharing the excitement of discovery through writing When he's not reading papers on his laptop, he's out mountain biking, bird watching and travelling the countryside. His other passions include drumming, photography and tinkering with vintage gizmos. Writing for Smore allows him to combine his fascination for the natural world with his passion for popular science communication.