Four Thousand Years of Carbon, Gone in Five Days

Quick summary

• Summer fires burned Welsh upland heath, moorland and grassland, including around 200 acres at Sychnant Pass, Conwy.

• Roughly 2,760 acres were affected across north Wales during the July peak, and 36 homes were evacuated.

• Prof Davey Jones told the BBC about 10cm of soil was lost at Sychnant Pass, unrecoverably.

• The MA's view: fuel load is the one wildfire variable upland land managers can act on.

One of the worst wildfire seasons in recent years

There are green shoots on the hillside at Sychnant Pass now, showing through the charred ground. Beneath them, on the estimate of the Bangor University team surveying the site, about 10 centimetres of soil has gone.

The fire responsible for that burned in July, one of the most significant of a season BBC News reports as among the UK's worst in recent years. Extreme heat and exceptionally dry conditions throughout July and August left heathland, moorland and upland grassland open to fire that moved quickly.

During the July peak, fires affected approximately 2,760 acres across north Wales alone. At Sychnant Pass, in Conwy county, around 200 acres were affected and 36 homes had to be evacuated.

Prof Davey Jones, who leads the Bangor survey, described the habitat there as a rare one, where "the UK is the epicentre globally" for its specialist plants, butterflies and insects.

What the Bangor team found below ground

Jones told the BBC that the visible damage is the smaller part of the story.

"People see the blackened vegetation and assume that's the main impact, but the real story is below our feet. This soil acts as a water sponge, a carbon store, a nutrient bank. Losing it is a double whammy, it worsens climate change and makes the habitat far more fragile."

His figure for Sychnant Pass is a field estimate given to the BBC, not a published result.

"We've lost all of that organic matter layer... 4,000 years of carbon gone in a single event," he said. "Once the topsoil is gone, we can never recover that." Thousands of years to form, and gone in perhaps five days.

Putting soil back is not ruled out, but what Jones described is a research problem rather than a technique. Designing artificial soils from organic wastes would first require knowing what the soil quality is now, he said, because such soils "don't exist yet".

The survey is in progress. Jones's team has been collecting samples at several Welsh sites before winter rain washes the remains off the hill, comparing burnt ground with adjacent unburnt ground to measure carbon, nutrients, microbial activity, water repellency and erosion risk. The researchers will return over the next two years to track recovery.

Why the green shoots mislead

Dr Kara Marsden, a lecturer in soil science working on the project, told the BBC that the regrowth does not mean what a visitor might assume.

"Bracken sprouts almost immediately because its rhizomes sit deep in the soil, so the burn layer wouldn't maybe have impacted those. But the heather and gorse have much shallower roots, so you know they're completely gone... that depth of soil they depend on could take thousands of years to form again."

The species coming back first are the ones whose growing points were below the burn. The heath community that gave the site its conservation value had roots in the layer that burned away.

Marsden said the team needed to be on site quickly, while the fire's effects were still fresh, to capture baseline data accurate enough to compare against in future sampling.

The cycle Prof Jones describes

Jones's wider warning concerns what each fire does to the odds of the next one. Fires release carbon, nitrogen and sulphur back to the atmosphere, and drier soils carry fire more readily than wet ones.

"Every time we have a wildfire, we're just making the problem worse and worse. It becomes a self-sustaining cycle... drier soils, more fires, more carbon released."

Without rapid restoration and better wildfire preparedness, he told the BBC, "we might lose pretty much all of this habitat within our lifetime".

Early evidence from the survey suggests vegetation can return, but more slowly and in a more fragile state, leaving the ground more open to burning again.

What we can learn from this

Soil that accumulated over millennia went in days, and the replacement Prof Jones suggested does not exist yet.

Land managers cannot change fire weather, and they cannot prevent every ignition. Fuel load is the part they can act on: how much dry leaf, stem and litter stands on the hill, and whether it runs unbroken across it. Controlled burning, cutting and targeted grazing reduce that quantity and break the continuity.

UK fieldwork backs this up. Davies and colleagues measured British moorland wildfires in 2011 and 2012. They found that the amount of vegetation burnt tracked how much was standing before the fire. How severely the ground burned depended on the weather and on the type of plants growing there.

Fuel management is not an alternative to peatland rewetting and restoration. Wet peat resists deep burning, but managed fuel reduces the chance that severe wildfire arrives carrying enough heat to reach it.

Doing that work takes trained people with the right equipment, in place before a fire starts.