Heather Burning and Carbon Loss: Questioning the Evidence Behind a Contentious Climate Claim

A major scientific review critically examines ten common claims regarding the effects of prescribed heather burning on peatlands in the UK, with "Prescribed heather burning causes a net peat carbon loss and contributes to the climate crisis" being the first claim reviewed.

The authors, including Dr. Andreas Heinemeyer, assert that this claim is unsubstantiated, too generic, site- and time-dependent, and affected by confounding factors, with insufficient robust data to support or negate it, and several datasets available to reject it.

Lack of Robust and Comprehensive Evidence

The primary argument against Claim 1 is the "paucity of empirical evidence" to conclusively demonstrate either a positive or negative effect of prescribed burning on carbon storage and emissions. The evidence that does exist is often limited, conflicted, or based on flawed methodologies. Key issues with the evidence base include:

• Limited Data and Uncertainty: Emissions data from UK peatlands managed by burning are limited and highly uncertain. Only about 30% of the UK's blanket bog is managed this way.

• Reliance on Single Studies: Supporting data often comes from single study sites, such as Moor House, which limits the generalizability of the findings.

• Conflating Wildfire with Prescribed Burning: Some studies incorrectly apply findings from intense wildfires to the impacts of controlled, low-severity prescribed burning.

• Methodological Limitations: Studies cited to support the claim, like Garnett et al. (2000), have methodological limitations. Similarly, peat core studies are limited in interpreting recent carbon accumulation and do not represent a full carbon budget.

• Incomplete Assessments: Carbon flux studies provide contradictory evidence, largely because they have not conducted a comprehensive assessment of the Net Ecosystem Carbon Balance (NECB) over an entire management cycle (e.g., ~20 years).

Countervailing Factors and Nuances Ignored by the Claim

The simple assertion that burning causes net carbon loss overlooks several complex and potentially positive factors related to carbon dynamics:

• Charcoal (Pyrogenic Carbon) Production: Burning converts some biomass into charcoal, a stable form of carbon that resists decomposition. This process can bypass decomposition and contribute to long-term carbon storage. Studies suggest charcoal may also suppress methane emissions, a potent greenhouse gas, although further research is needed.

• Suppressed Peat Decomposition: Evidence suggests that low-severity fires may suppress the decomposition of existing peat, further aiding long-term carbon storage.

• Vegetation Rejuvenation: Rejuvenating heather through burning can stimulate net carbon uptake over time as younger, more vigorous plants have a higher efficiency of photosynthesis. Conversely, unmanaged, ageing heather can lead to a decline in water table depth and increased net carbon losses.

• Root Carbon Input: Heather is a peat-forming species, and its root system is an important source of carbon input into the peat, a factor often overlooked in simple carbon loss calculations.

Relative Contribution to Climate Change

Even if the claim were true, the sources argue that the contribution of controlled heather burning to climate change would likely be insignificant when placed in a wider context. For instance, emissions from all "modified bog" categories (heather, grass, eroding) are estimated to be less than 10% of total UK peatland emissions, whereas lowland agricultural peatlands account for approximately 60% of the UK total.

Recommendations for Future Research

To address the evidence gaps surrounding Claim 1, the authors recommend a more rigorous methodological approach. The "gold standard" would be a randomized, multi-site, catchment-scale, Before-After-Control-Impact (BACI) experimental design. Such studies should:

• Assess all components of the Net Ecosystem Carbon Balance (NECB).

• Cover the entire management cycle (e.g., 20+ years) to capture long-term trajectories rather than just short-term disturbances.

• Compare burning robustly against alternative management scenarios like mowing or no management.

In conclusion, the claim that prescribed heather burning causes a net peat carbon loss and contributes to the climate crisis is presented as an oversimplification that is not supported by the current, complex, and often contradictory body of scientific evidence.

The debate has been polarized by such claims, and the authors call for a renewed focus on building a more robust and unbiased evidence base to inform future policy and management decisions.

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