Dr Ruth Mitchell, of the James Hutton Institute, shares her reflections of treescapes
‘Treescapes’ is a word that is being used increasingly to described landscapes in which trees play a significant role. Treescapes can include plantations, native woodlands, and smaller patches of trees in agriculture or urban settings. Many of us are aware of the value of trees and the benefits we receive from them, including the biodiversity they support, the enjoyment we get from walking through woodlands and the commercial value of the timber.
Recently an expansion in treescapes has been identified as a major part of the UK government’s plans to meet its target of net zero carbon emissions by 2050. The UK Committee on Climate Change has recommended planting at least 30,000 hectares per year (90-120 million trees) of broadleaf, mixed or conifer woodland – a substantial increase from the current 9,000 hectares per year, which will increase UK forest cover from 13% to at least 17% by 2050. The simple logic being that trees store carbon and reduce the carbon dioxide in the atmosphere. However, it’s not actually quite as simple as that. This logic forgets the huge amounts of carbon stored in the soil in many upland areas and any impact tree planting may have on this carbon store. Recent modelling work[i] mapped potential changes in ecosystem carbon storage following woodland creation. The study predicts that conversion from semi-natural land to woodland can result in net carbon loss for the first 20 years and, in some scenarios, it may be 80 years or more before woodlands provide a carbon benefit. These predicted carbon losses result from soil disturbance, which might suggest these losses can be avoided if forests establish by natural regeneration. However, recent experimental work has also shown that soil carbon losses can occur even with minimal soil disturbance during tree establishment on heather moorland[ii]. These losses are unexplained but may be due to functional changes that occur in the soil microbial community during tree colonisation.
The other benefits associated with an expansion in treescapes, such as increased biodiversity, should also not be assumed to automatically occur once trees are planted. The value of woodland for biodiversity will depend on which tree species are planted, the structure of the woodland created and how it is managed in the long-term. We need to think beyond just establishing trees, whether by planting or natural regeneration, to their long-term management. The phrase “the right tree in the right place” is often used now-a-days, but defining what we mean by the right tree and right place will depend on peoples objectives, values and opinions.
A paper has recently been published entitled, “Ten golden rules for reforestation to optimize carbon sequestration, biodiversity recovery and livelihood benefits”[iii]. The rules are:
(1) Protect existing forest first;
(2) Work together (involving all stakeholders);
(3) Aim to maximize biodiversity recovery to meet multiple goals;
(4) Select appropriate areas for restoration;
(5) Use natural regeneration wherever possible;
(6) Select species to maximize biodiversity;
(7) Use resilient plant material (with appropriate genetic variability and provenance);
(8) Plan ahead for infrastructure, capacity and seed supply;
(9) Learn by doing (using an adaptive management approach);
(10) Make it pay (ensuring the economic sustainability of the project).
Many of us may be able to agree with these rules but the challenge is in implementing them, to think beyond a target number of trees to be planted, to think about the long-term management of the trees and how to ensure they create the desired environment for our grandchildren and great grandchildren.
I suggest that as the debate about tree planting, climate change, net zero and the biodiversity crises rages we need to be much more nuanced in our approach. While acknowledging that we do need action now to help reduce the climate emergency, tree planting is not the only action we can take. I hope that in the rush to lock up carbon we are not storing up problems for the future as we did when we planted the flow country with conifers. Woodlands are great and can bring many benefits in relation to both the climate and biodiversity crises, but as always with ecology and the intricacies of the natural world, it’s a complicated story. Tree establishment schemes shouldn’t be a one size fits all approach, they need to be flexible enough to allow a range of different tree species to be established, at different sites, using different mechanisms, without diminishing overall well-being both now and into the future.
Dr Ruth Mitchell
A plant and soil ecologist at the James Hutton Institute Aberdeen.
All opinions expressed are solely those of the author not of the James Hutton Institute
[i] MATTHEWS, K. B., WARDELL-JOHNSON, D., MILLER, D., FITTON, N., JONES, E., BATHGATE, S., RANDLE, T., MATTHEWS, R., SMITH, P. & PERKS, M. 2020. Not seeing the carbon for the trees? Why area-based targets for establishing new woodlands can limit or underplay their climate change mitigation benefits. Land Use Policy, 97, e104690. [ii] FRIGGENS, N. L., HESTER, A. J., MITCHELL, R. J., PARKER, T. C., SUBKE, J. A. & WOOKEY, P. A. 2020. Tree planting in organic soils does not result in net carbon sequestration on decadal timescales. Global Change Biology, 26, 5178-5188. [iii] Sacco, A.D., Hardwick, K.A., Blakesley, D., Brancalion,P.H.S., Breman, E., Rebola, L.C., Chomba, S., Dixon, K., Elliott, S., Ruyonga, G., Shaw,K., Smith,P., Smith, R.J., Antonelli, A. 2021 Ten golden rules for reforestation to optimize carbon sequestration, biodiversity recovery and livelihood benefits. Global Change Biology, DOI: 10.1111/gcb.15498