Claim That ‘Rewetting Cuts Wildfire Risk’ Remains Unproven

A major scientific review critically examines ten common claims regarding the effects of prescribed heather burning on peatlands in the UK, with “Rewetting reduces heather dominance and thus protects peatlands against wildfire" being the fourth claim reviewed.

The authors, including Dr. Andreas Heinemeyer, consider the claim unsubstantiated, lacking direct, applicable evidence from UK upland peatlands. The review critiques the claim's underlying assumptions, highlighting the complexity of peatland ecology and the limitations of current research.

Critiquing the Causal Relationship

The claim rests on a proposed causal chain: rewetting peatlands leads to a decline in heather, which in turn reduces fuel loads and makes the landscape more resilient to wildfire. However, the report argues that this relationship is not supported by robust evidence.

• Lack of Direct Evidence: The review states there is "no directly applicable evidence to support such generic assumptions". The idea that rewetting will limit heather cover and negate the need for fuel management is described as remaining unevidenced. In fact, the review points out that the concept has "never been tested within UK upland peatlands".

• Heather's Tolerance to Wet Conditions: A key counterargument is that heather (Calluna vulgaris) can thrive in a wide range of water table depths, including very wet conditions. The review cites studies showing that heather can be physiologically adapted to wet environments and can maintain high cover on both dry and wet blanket bog sites. This challenges the fundamental assumption that simply raising the water table will eliminate heather dominance.

• Dependence on Unrelated Studies: Claims supporting rewetting as a tool to reduce heather are sometimes based on studies that are not applicable to the UK upland context, such as those on the restoration of industrially drained and mined bare peat.

Wildfire Risk and Fuel Load Management

The review emphasizes that wildfire risk is determined by a combination of fuel load, fuel moisture, and weather conditions. It argues that rewetting alone may not sufficiently address these factors, especially in the face of climate change.

• Ageing Heather as a Fire Risk: The reviews presents a counter-narrative where unmanaged, ageing heather can increase fire risk. Older, taller heather has been shown to dry out the surface peat over time, and the accumulation of biomass creates a higher fuel load. This combination increases the risk of more severe wildfires that could ignite the peat itself.

• Limitations of Rewetting: While rewetting can generally reduce fire risk, especially the danger of fires burning deep into the peat, it does not make peatlands "fireproof". During extreme hot and dry weather conditions, even typically wet ground and vegetation can become dry and highly flammable, particularly where fuel loads are high.

• Cessation of Burning and Increased Fuel Load: Stopping prescribed burning can lead to a significant increase in above-ground biomass, thereby increasing the fuel available for potential wildfires. This could result in hotter and more damaging fires if they do occur.

The Need for a Site-Specific and Evidence-Based Approach

The review strongly advocates for moving away from generalized statements and toward site-specific assessments and robust experimental designs.

• Natural Limitations: There are natural limits (e.g., climate, topography) to how wet a particular site can become, and not all sites are drained, meaning rewetting potential is limited or non-existent in some areas.

• Lack of Long-Term Monitoring: A major gap identified is the lack of robust, long-term monitoring of restoration projects using a Before-After-Control-Impact (BACI) design. There are seemingly no studies that have specifically tested the assumption that rewetting mitigates wildfire risk in UK peatlands.

• Future Research Needs: To validate the claim, the review recommends measurements, trials, and models to test if, where, and to what extent rewetting provides wildfire resilience. This is particularly critical in the context of climate change, which is expected to bring warmer, drier conditions that increase fire risk.

In summary, the report concludes that Claim 4 is an unsubstantiated and overly simplistic solution to the complex issues of heather management and wildfire risk on UK peatlands.

The evidence suggests that heather is more resilient to wet conditions than is often assumed, and that ceasing fuel management in favor of rewetting alone could paradoxically increase the risk of severe wildfires by allowing fuel loads to build up.

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