Why Suppressing Fire Without Managing Fuel Makes the Next Blaze Worse

A fire ecologist's research on savannahs, forests and deserts carries one blunt lesson for any landscape that burns, and it extends to our uplands.

Stop fire from happening and you have not removed the danger. You have let fuel build for a fiercer fire later.

That is the part of Dr Kimberley Simpson's argument that working uplands cannot afford to skim past. Dr Simpson, a research fellow at the University of Sheffield's School of Biosciences, studies how plants and fire shape one another. Her field sites are tropical savannahs, boreal forests, rainforests and the deserts of the American south-west, not British moorland, which she does not mention.

On a recent episode of the university's That's Science podcast Dr Simpson set out why treating fire as nothing but a disaster gets the science wrong.

What Dr Simpson actually said

Fire is older than us, and it is not our doing

Dr Simpson's first target is the idea that fire is a human invention. By her account the earliest evidence of fire on Earth goes back around 420 million years, long before people, and arriving soon after plants colonised land and supplied two of the three things fire needs: bulk fuel, and the oxygen they released through photosynthesis.

The third is an ignition source. People have used fire as a tool for thousands of years, she notes, but we did not start it.

Some plants now need fire to reproduce

Over that history, she says, many plants did not merely tolerate fire but came to depend on it:

• Lodgepole and other pines seal their seed in resin-bonded cones that open only when a fire's heat melts the resin.

• Gorse (her one British example) carries hard-coated seed that cracks open after burning, letting water in to trigger germination.

• Some species flower only once fire has passed, from South Africa's flame lily to a Brazilian plant she describes going from charred stump in the morning to flower buds the same afternoon.

Take fire away from these systems, she says, and the species built around it struggle.

The "reset button"

A freshly burnt landscape looks dead. Dr Simpson describes it instead as cleared ground: competitors gone, light and water freed, a nutrient-rich ash layer left for whatever germinates first.

Fire resets the cycle of vegetation and keeps open-ground species in the mix that a maturing, unburnt landscape would shade out. Her shorthand is "pyrodiversity equals biodiversity": a varied pattern of fire across a landscape supports more species than no fire at all.

It only works to a rhythm

Plants are adapted not to fire in the abstract but to a particular interval, by her figures perhaps five years in a tropical grassland and a century or two in a temperate or boreal forest.

Climate change is the threat because it breaks that rhythm, bringing hotter, more frequent fires and a longer season that strikes species before they have recovered.

Where this touches the uplands

Dr Simpson draws no conclusions about heather, peat or British policy, and we are not putting words in her mouth. But one passage states a principle that does not stop at her study sites.

Asked how fire-prone landscapes should be handled, she rejects suppression as a strategy: you can hold fire off for a while, but a heatwave or a stray spark means it returns, and if nothing has been done about the vegetation in the meantime, it returns to far more fuel.

The result, in her words, is a fire hot enough to "burn into the soil." She adds that blanket suppression is often not even desirable, and that the long-running suppression policies once imposed on some savannahs are now judged a mistake.

That is the Moorland Association's case in a sentence, reached from the other side of the world. Where fire cannot be excluded, and on dry heather in a hot spring it cannot, the real choice is not between fire and no fire.

It is between managed fire that keeps fuel loads down and the unmanaged kind that waits for the worst possible day. This is why we press for controlled burning to be judged as a wildfire-prevention tool on its evidence, and why we question policies that restrict it while presenting peat rewetting, on its own, as a sufficient wildfire defence.

Fuel that is not removed by a cool, managed burn does not vanish. It waits for a hot one.

On ground that will burn whatever we do, the only decision left is when and how hot, and that decision is made years in advance by how much fuel we allow to build.