Wednesday, 30 May 2012

Is "Bringing Woodland Back into Management" good for the Climate?

A number of current forestry lobbying documents include the suggestion that the global atmosphere would be benefited if currently unmanaged broadleaved woodlands in England were brought into active management for woodfuel. This post seeks to explore whether there is scientific evidence in support of such a policy.

The "Our Forests" lobbying group provide an example of the assertion:

"We need to bring our neglected woods back into productive rotation to kick-start local, low-carbon economies, boost rural employment, and create the right conditions for wildlife."

In stating this, Our Forests draw upon the comments of Wildlife link on the Forestry Commission's Woodfuel Strategy:
 
“The Woodfuel Target could play a key role in contributing to a new low-carbon economy and in addressing the urgent need for positive management of many woods and forests across the country.”


The Woodfuel Strategy itself, a product of a civil service careful to ensure "evidence based policymaking", does not make such a broad claim. 

The suggestion is that burning wood would reduce fossil fuel usage, while the woodland growth would re-sequester the CO2 emitted as a result of burning the woodfuel. However there is some doubt about whether the scientific evidence supports such a general policy.

The most comprehensive assessment of the potential role of UK forests in mitigating climate change is the "Read Report" published by the Forestry Commission in 2009. This report set out a number of Forest Management Scenarios (FMS). One of these, (FMS-D) dealt with the bringing of unmanaged woodlands back into management. It is shown by the light blue line on the graph (reproduced from Read) below.






Here is the related quote from the "Read Report" 
"Bringing unmanaged woodlands back into management (FMS-D) leads to significant net emissions (up to 5.5 MtCO2 year1) from forest biomass and soils relative to the BAU scenario. However, this impact is reduced when total abatement is considered, with the result that over the full course of the simulation to 2150..., FMS-D provides a small amount of additional abatement (0.3 MtCO2 year1)."

The implication is that a programme of increased management of broadleaved woodland in England of the type modelled, could result in a negative net effect on atmospheric CO2 for a long, perhaps crucial, period.

The reason given for this (perhaps counter intuitive) result is that:
"the majority of unmanaged woodland is slow-growing, broadleaved woodland for which both levels of production (and therefore substitution) and rates of recovery in carbon stocks following harvesting are smaller than for faster growing conifer species. The age and current growth rate of a stand brought back into management will also have a profound effect on the balance between substitution benefi ts and recovery of carbon stocks, requiring more detailed knowledge than available as input to this national scale evaluation."

Similar effects have been reported for slow growing boreal forests (Holtsmark, 2011), and more generally from increased additional forest biomass harvesting (Schulze et al 2012).

 

Conclusion

In the absence of the more "detailed knowledge" referred to by Read et al., carbon science does not appear to support a general policy of increasing the management of broadleaved woodland in England for woodfuel, in order to mitigate climate change. The global atmosphere might be better protected by refraining from human interference in such woodland, leaving nature to sequester carbon by continued growth.

Refs:

Read, D.J., Freer-Smith, P.H., Morison, J.I.L., Hanley, N., West, C.C. and Snowdon, P. (eds). 2009. Combating climate change – a role for UK forests. An assessment of the potential of the UK’s trees and woodlands to mitigate and adapt to climate change. The Stationery Office, Edinburgh.

Schulze, E.-D., K├Ârner, C., Law, B. E., Haberl, H. and Luyssaert, S. (2012), Large-scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral. GCB Bioenergy. doi: 10.1111/j.1757-1707.2012.01169.x

Holtsmark B (2011) Harvesting in boreal forests and the biofuel carbon dept. Climatic Change, Available on-line:
http://www.ssb.no/publikasjoner/pdf/dp637.pdf

5 comments:

  1. Damn it, now that i know that I'll have to go back to burning coal then! or could i plant fast growing conifers in those canopy gaps?

    ReplyDelete
  2. I purposely refrained from dealing with biodiversity, rural economy etc in this post. I wanted to focus purely on the carbon science and calculations and the integrity of some of the (I suspect sentimental) arguments from the "woodland management lobby".

    So, being "true to truth" in carbon terms I'd have to agree. Underplanting with Western Hemlock would probably maximise carbon abatement.

    ReplyDelete
  3. On that basis then, I'll continue thinning my broadleaved woodlands, in order to concentrate the carbon sequestration in valuable sawlogs which i can cut down at a later date to produce furniture which will lock up the carbon for centuries. The thinning I'll use for domestic heating, rather than buying fossil fuels.

    ReplyDelete
  4. The model includes the carbon benefit from sawlogs, furniture (including the locked up for centuries angle) as well as firewood instead of fossil fuels? The Read report does say that the result may be modestly positive by 2150, so it would be hard to suggest thinning was doing much harm on that timescale. (Note - I have been in correspondance with one of the contributors to "Read" who has suggested that the positive values for this may be "conservative" E.g. your furniture point may be stronger than in the model, I'll do an update on this.)

    So - the numbers suggest that by 2150 you could claim a modest climate benefit from what you propose. I'm afraid the model still suggests thinning might be negative for the atmosphere in the medium term?

    I think my main point is that some forestry lobbyists are suggesting that bringing woodland into management is a carbon "public benefit" and thus seeking a management subsidy? If an owner can thin at a profit without taxpayers help, I think it would be rather hard if we were to penalise them for the net carbon emmissions 2030 to 2080. However the woodlands we are talking about are already neglected. This is presumeably because it does not currently make business sense to thin them in the free market, even with no income tax on timber revenue?

    So if thinning such a woodland made me money in a free market, I too would be tempted to do it, knowing that I might be damaging the climate until 2080, but benefiting it from then on.

    ReplyDelete
  5. There is also evidence that innefficiently burning wood can result in more black carbon, damaging for human health and climate.

    http://www.guardian.co.uk/environment/2011/nov/27/wood-fires-fuel-climate-change

    ReplyDelete