Carbon, wildlife, timber – not all combinations work

On a global level one of the best solutions to the climate and biodiversity crises is to leave forests unharvested, or to harvest only at the levels currently done by indigenous populations; and to allow logged forest to regrow without further logging. This minimal interventionist approach is likely to give high benefits in both biodiversity and carbon sequestration terms.

This approach does however raise issues and questions if we try to apply it, or research based on examples from elsewhere in the world, to British conditions. Our conservation priorities are largely based on the type of cultural landscapes that have dominated our island for at least the last two millenia (Rackham, 1986; Ratcliffe, 1977), managed grassland, heathland, moorland and woodland. Much conservation effort has gone into maintaining or restoring coppice regimes in ancient woodland, restoring livestock grazing to wood-pastures, clearing young regeneration from around veteran trees and repollarding them.

We could say that this ‘traditional management’, i.e the sorts of pre-industrial farming and forestry practices that predominated prior to the 19th century is our nearest equivalent to promoting ‘indigenous’ cultural use. However it is clearly nowhere near minimal-intervention. Moreover, traditional management ran alongside and was part of a steady intensification of land-use for the last thousand years. Species were going extinct in Britain (Hambler et al., 2011) and there was a reduction in overall tree and woodland cover in the landscape, from c15% in AD 1086 to about 5% in AD 1900, (Rackham, 2003) even before the increased rates of loss in the post-WWII era.

On many sites traditional management has been successful in conserving the plants and animals that we have collectively come to value. It is not the right approach everywhere, e.g. Hambler and Speight (1995) and the desire, necessity, to increase carbon sequestration now adds a further complication. Many of our ancient woods are composed of young growth, a legacy of wartime felling and coppice management prior to that. They are building up carbon stocks in the trees and in the soil and will do so for many years to come, if left undisturbed under minimum intervention (Woodland Trust, 2021). However that approach goes against restoring traditional management such as coppicing to benefit many vulnerable and valued species as George Peterken has discussed with respect to Lady Park Wood (Peterken and Mountford, 2017). Coppicing removes most of the above-ground carbon stock in the tree and shrub layer, promotes litter breakdown and disturbs the soil surface increasing loss of soil carbon. The harvested material tends to go into relatively short-lived products such as firewood, charcoal, pea and bean sticks, etc. so the carbon is soon back in the atmosphere. Even though the coppice regrows the average amount of carbon stored above-ground over the rotation is less than under minimum intervention.

Opening-up former wood-pastures that scrubbed up in the last eighty years under reduced grazing/minimum intervention and haloing around veteran trees similarly reduces the above-ground carbon store. Grazed wood-pasture will be building up carbon stocks in the soil under the grassland, but much of the photosynthate (probably most?) is being recycled back to the atmosphere quickly through the respiration of the large herbivores and then the eaters or the decomposers of their bodies, dung etc. Old trees and old growth stands can be net carbon sinks (Luyssaert et al., 2008; Stephenson et al., 2014), but this is unlikely to be true where the tree canopies are declining through crown retrenchment, the trunks are losing mass through hollowing, and there are only a few old trees per hectare.

We have a dilemma. In British woodland what might be best for the woodland species we have traditionally valued might not be best for carbon sequestration in the forest; locking up carbon in the trees in minimum intervention stands also means that they cannot provide wood and wood products for use; so, we continue to export our environmental footprint through our high dependence on imported wood and wood-products.

We need more tree and woodland cover but as part of a mixed economy: there is no single simple solution.  Expanding trees and woodland will allow more opportunities to store carbon and in managed stands to increase home-grown production; but these new trees and woods will take many decades to build up their wildlife value. We need to manage many of the ancient woods in something equivalent to traditional practices to ensure we do not in the meantime lose more of the species that are part of our cultural heritage; but this will limit the carbon storage potential of those woods. We need to accept that our wildlife is going to change, with both gains and losses in abundance if not of actual species extirpations, in both the new woods created and in the ancient woods left for carbon sequestration through minimum intervention. We cannot have our full carbon cake, and historic wildlife communities, and a good harvest of sustainably grown timber, all on the same bits of land.

HAMBLER, C., HENDERSON, P. A. & SPEIGHT, M. R. 2011. Extinction rates, extinction-prone habitats, and indicator groups in Britain and at larger scales. Biological Conservation, 144, 713-721.

HAMBLER, C. & SPEIGHT, M. R. 1995. Biodiversity conservation in Britain: science replacing tradition. British Wildlife, 6, 137-147.

LUYSSAERT, S., SCHULZE, E.-D., BÖRNER, A., KNOHL, A., HESSENMÖLLER, D., LAW, B. E., CIAIS, P. & GRACE, J. 2008. Old-growth forests as global carbon sinks. Nature, 455, 213.

PETERKEN, G. F. & MOUNTFORD, E. P. 2017. Woodland development: a long-term study of Lady Park Wood, Wallingford, UK, CABI.

RACKHAM, O. 1986. The history ofthe countryside, London, Dent.

RACKHAM, O. 2003. Ancient woodland: its history, vegetation and uses in England (revised edition), Dalbeattie, Scotland, Castlepoint Press.

RATCLIFFE, D. A. 1977. A nature conservation review, Cambridge, Cambridge University Press.

STEPHENSON, N. L., DAS, A., CONDIT, R., RUSSO, S., BAKER, P., BECKMAN, N. G., COOMES, D., LINES, E., MORRIS, W. & RÜGER, N. 2014. Rate of tree carbon accumulation increases continuously with tree size. Nature, 507, 90-93.

WOODLAND TRUST, W. 2021. State of the UK’s woods and trees 2021. Grantham: Woodland Trust.

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