The Rewetting Claim That Hasn't Been Tested

One of the most influential ideas in the wildfire debate, that wetting a bog removes its flammable heather, and the need to manage it , turns out never to have been directly tested. And the evidence we do suggests otherwise.

Quick summary

• A popular restoration claim: wetting a bog thins its heather and removes the need for fuel management.

• But this specific claim has never been directly tested on UK upland peatlands.

• And the evidence we have shows heather thriving on wet bog just as thickly as on dry.

• Rewetting still protects the deep peat, but the surface fuel remains a separate job.

Much of the case for rewetting-alone rests on a tidy idea: raise the water table, and the moor slowly loses its dense, flammable heather in favour of wetter, harder-to-burn bog vegetation.

Do that, the argument goes, and in time you no longer need to actively manage the fuel on top, the wet ground does it for you. The idea is influential. It underpins parts of the IUCN's position on burning and peatlands and appears in Natural England evidence reviews. But when you look for the evidence that it actually works, a gap opens up.

The claim, stated fairly

It's worth putting the argument at its strongest, because the weak version is a straw man. Nobody serious thinks heather drops dead the moment you block a drain.

The real claim is about trajectory: that over years and decades, higher water tables tip the balance away from tall, woody, fuel-heavy heather and towards Sphagnum and bog species that carry fire far less readily, so the restored moor eventually keeps its own fuel in check without cutting or burning.

That's a reasonable hypothesis. The problem is that it is still a hypothesis.

What's actually been tested

In 2025, a peer-reviewed review in Mires and Peat led by Andreas Heinemeyer assessed ten common claims about heather and peatland management against the evidence.

The claim that rewetting reduces heather dominance and thereby protects peatlands from wildfire was rated unsubstantiated: there is no directly applicable UK evidence that raising water tables removes established heather dominance, and using rewetting in this way to mitigate wildfire has never actually been tested on UK upland peatlands.

This isn't only one team's reading. NatureScot's own official evidence review of muirburn and wildfire (Report 1302), commissioned by the government's statutory conservation body, reaches a similarly cautious conclusion about how thin the direct evidence is on every side of this question.

When an independent government review and a separate academic review both arrive at "we don't actually know," it is hard to dismiss as one camp's spin.

What the evidence does show

Heather is a tough, adaptable plant that grows perfectly well with wet feet. An independent field study by Grau-Andrés and colleagues (2018) compared a dry heath with a raised bog of deep, saturated peat and found both thoroughly dominated by heather, wet ground and all.

The longer-term picture is the same. Across a decade of monitoring on blanket-bog sites in northern England, heather covered roughly three-quarters of the ground on the wettest and driest sites alike, and the tallest mature heather of all was growing on the wettest site.

That's a modest evidence base: it's a handful of sites, "wettest" means the wettest of the monitored bogs rather than a fully restored one, and heather's grip may partly reflect a long history of management.

But it matches the independent work. If wetting reliably thinned heather, this is not the pattern you would keep finding.

Where rewetting genuinely does work

None of this makes rewetting a waste of effort, far from it. Raising water tables is one of the best things we can do for a bog.

The same review is explicit that rewetting should generally reduce fire risk and limit the chance of a fire burning down into the peat itself.

Wet bog is also genuinely more resistant to severe burning: Grau-Andrés's study found the saturated bog far less sensitive to fire severity than the dry heath, and a recent 27-site Scottish study likewise found wet blanket bog and wet heathland resisting severe fire where the ground was wet enough.

The point is precise. Rewetting reaches the peat, the deep, smouldering fire.

The heather standing above it, the surface fuel that carries the fast-moving flames, is left untouched, and it dries on its own terms: heather becomes flammable once its moisture drops below about 60%, which can happen on a dry, breezy spring day whatever the water table is doing below.

Even the Scottish study found wet moorland can burn once conditions turn hot and dry enough.

The honest bottom line

To be fair to the restoration case, an untested idea can still turn out to be right. It's entirely possible that decades of high water tables would eventually shift a moor's vegetation and its fire behaviour.

The Heinemeyer review is, above all, a call for exactly the trials that would settle it, long-term, multi-site, before-and-after comparisons.

The sensible conclusion is to manage each site on its merits. Keep the water in the ground and keep the fuel in check with controlled burning and cutting, and back the research that would settle the question, instead of applying one blanket rule to every moor.

Why this matters

Rewetting is worth doing for its own sake, but if we treat an untested idea as settled fact, we'll keep being caught out by fires on ground we thought we'd fixed, because the water and the fuel are two different problems, and each needs its own answer.