Summary
Afforestation results in sequestration of atmospheric CO2 as trees grow. Forests planted on mineral soils are generally accepted to result in increased soil C content. In some circumstances, afforestation on organo-mineral (e.g. peaty gleys, peaty podzols) or organic (e.g. deep peats) soils may result in substantial loss of soil C due to soil disturbance during forest planting. However, there is little quantitative evidence for such impacts.
Assessment of soil carbon stocks after afforestation in England and Wales
Summary
This project was commissioned by the Forestry Commission to provide more robust evidence of soil carbon change and sequestration potential after afforestation. A soil resurvey was carried out by Cranfield University on selected sites from the Soil survey of England and Wales which have changed land use to forestry in the past 30-40 years. Results, bringing together soil and forestry information in order to calculate the change and rates of changes of soil carbon and other soil properties due to forest creation, will contribute to the evaluations of overall GHG mitigation potential of forestry and the Woodland Carbon Code.
Research objectives
Cranfield University has an inventory of sites where soil samples were taken from each soil horizon down to the parent material and analysis of basic soil properties was conducted as part of the National Soil Survey of England and Wales between the 1960s and 1980s. The aims of the present study were to:
- Select suitable sites for re-sampling, based on afforestation since previous sampling (a total of 20 sites),
- re-visit sites and sample all soil profiles, to determine soil pH, carbon and nitrogen stocks of each horizon and of archived samples.
Results
This research provided valuable information guiding the likely direction and rate of change of soil C stocks due to afforestation. Trends indicated that afforestation was neutral or slightly positive for soil C sequestration when sandy soils like podzols are converted to conifer forestry. Increasing surface organic layers under afforestation provided the highest C stock increase under all forest types, on all soil types and from all previous land uses, compared to mineral soils (where the main C losses were observed).
Full details and results of this project will be available soon.
Status
A new feasibility study has been commissioned to create a database of all data available from experiments and soil surveys and resurveys aiming at afforestation impacts on soil carbon stocks.
Contact
Funders and partners
The research was undertaken in collaboration with NSRI, Cranfield Universityand Forestry Commission.
Forestry Commission policy
At the core of the Government’s policy on sustainable forest management is the need to safeguard soil and water resources. Human actions, from local scale forest operations to international scale climate change and air pollution may compromise forest soil sustainability with consequential impacts on the freshwater environment. Poorly planned and managed forests can severely degrade soil and water resources, making forests more vulnerable to climate change. Good management, in contrast, seeks to maintain and enhance the natural protective functions of forests and the benefits they provide for society, including carbon sequestration, clean water and reduced flood risk. The overall objective of this programme is to evaluate through measuring, modelling and mapping the impacts of forests, woodlands and management practices on soil and water resources under a changing climate and changing pollutant emissions. It also aims to quantify the benefits of woodland creation for soil, water and flood management and evaluate the role of woodland in integrated catchment management. The findings will improve our understanding of the nature of these impacts and be used to help develop practices and guide future policy to secure the soil and water services that underpin the multiple benefits provided by forests.
Changes to C stocks in Scottish soils due to afforestation
Summary
This project was commissioned by Forestry Commission to provide more robust evidence and quantification of the changes in soil carbon stocks and other properties in land use conversion to forestry. The project was led by JHI and involved re-sampling of the sites from the National Scottish Soil Survey which have undergone land use change to forestry in the past 30-40 years. A review of the soil data held in the Scottish Soils Database at The James Hutton Institute identified 40 sites on land owned by the Forestry Commission (FC) that had been afforested after the original description and sampling of the soil. These sites provided an opportunity to assess the extent of changes in soil carbon over time for a range of soil types and under different tree species.
Research objectives
The aims of this project were to:
- relocate these sites and collect new soil morphological data,
- analyse the samples for a range of soil properties (but primarily soil organic carbon concentration),
- assess and calculate the changes in soil carbon stocks
Fixed depth sampling alongside the traditional sampling by horizon (layers) was included as a way of attempting to integrate the BioSoil and NSIS sampling schemes in order to develop a more substantial database of afforested soils in Scotland.
Results
This research demonstrated that long-term afforestation of soils previously under moorland vegetation generally leads to an increase in soil carbon, expressed either on a total change or annual change basis and that this increase can largely be accounted for by the increase in thickness and carbon content of the litter layer. Data from this project will be used as input into models and site assessments to evaluate the amount of above- and below-ground carbon that is stored within the soils and trees.
Status
Project completed in 2016, with further research ongoing.
Contact
Funders and partners
Research collaborators include:
• CFS/FC Scotland
Forestry Commission policy
At the core of the Government’s policy on sustainable forest management is the need to safeguard soil and water resources. Human actions, from local scale forest operations to international scale climate change and air pollution may compromise forest soil sustainability with consequential impacts on the freshwater environment. Poorly planned and managed forests can severely degrade soil and water resources, making forests more vulnerable to climate change. Good management, in contrast, seeks to maintain and enhance the natural protective functions of forests and the benefits they provide for society, including carbon sequestration, clean water and reduced flood risk. The overall objective of this programme is to evaluate through measuring, modelling and mapping the impacts of forests, woodlands and management practices on soil and water resources under a changing climate and changing pollutant emissions. It also aims to quantify the benefits of woodland creation for soil, water and flood management and evaluate the role of woodland in integrated catchment management. The findings will improve our understanding of the nature of these impacts and be used to help develop practices and guide future policy to secure the soil and water services that underpin the multiple benefits provided by forests.
Soils and the Woodland Carbon Code
Summary
The Woodland Carbon Code is the voluntary standard for UK woodland creation projects where claims are made about the carbon dioxide they sequester. Research is still ongoing to fully understand the changes to soil carbon as a result of land-use change to forestry and forest management activities.
Research objectives
We are working to ensure that soil carbon emissions associated with the woodland creation project are quantified and that any soil carbon sequestration associated with the woodland creation project is accurately accounted for.
Results so far
Our projects which are supporting the Woodland Carbon Code include:
- Changes to C stocks in Scottish soils due to afforestation
- Assessment of soil carbon stocks after afforestation in England and Wales
- Long-term impact of Sitka spruce afforestation on carbon stock of peaty gley soils
- Soil changes under long-term woodland establishment
Further research in the next 2-3 years will allow us to develop more reliable figures for rates of soil carbon accumulation. Results of this research will be used in the next Woodland Carbon Code update on soil carbon. Projects will be able to update their soil carbon estimates at the first verification, based on this research and update.
Future Developments
- Reviewing results from all ongoing afforestation projects in the UK to provide better quantification of the C sequestration potential of forest soils to be accounted for in the Woodland Carbon Code’s overall GHG mitigation potential.
- We will develop a soil assessment protocol which, through field survey, will aid the identification of soil type as well as quick estimation of soil carbon content based on main soil type and humus type.
Status
Ongoing
Contact
Funders and partners
This approach is being developed with the support of a group of soil experts from across the UK, including researchers from The James Hutton Institute, University of Aberdeen and University of Edinburgh.
Forestry Commission policy
At the core of the Government’s policy on sustainable forest management is the need to safeguard soil and water resources. Human actions, from local scale forest operations to international scale climate change and air pollution may compromise forest soil sustainability with consequential impacts on the freshwater environment. Poorly planned and managed forests can severely degrade soil and water resources, making forests more vulnerable to climate change. Good management, in contrast, seeks to maintain and enhance the natural protective functions of forests and the benefits they provide for society, including carbon sequestration, clean water and reduced flood risk. The overall objective of this programme is to evaluate through measuring, modelling and mapping the impacts of forests, woodlands and management practices on soil and water resources under a changing climate and changing pollutant emissions. It also aims to quantify the benefits of woodland creation for soil, water and flood management and evaluate the role of woodland in integrated catchment management. The findings will improve our understanding of the nature of these impacts and be used to help develop practices and guide future policy to secure the soil and water services that underpin the multiple benefits provided by forests.
Research Objectives
We have recently undertaken a range of research projects to provide a more robust evidence base for soil carbon stocks and their change and potential long term carbon sequestration after afforestation on a range of soils across the UK.
Findings and recommendations
Afforestation on mineral soils
Forests planted on mineral soils are generally accepted to result in increased soil carbon (C) content; furthermore, if the mineral soil has a high clay texture, most of the carbon (70%) will be of stable form, as evaluated by Villada, 2013 from the UK BioSoil soil network sites thus aiding long term carbon sequestration into the soil. Positive soil C rate of change has been measured along a 200 years of Oak chronosequence on heavy clay soils at Alice Holt. Our research into Short Rotation Forestry (SRF) indicates that soil C sequestration is the highest on arable soils that previously had very low soil C content. Leaf litter inputs and tree rooting will enrich the low soil carbon levels, improving soil quality and biodiversity.
Further information on our research into the effects of SRF on mineral soils is available on our Short-Rotation Forestry effects on soil page.
Afforestation on organo-mineral soils
A review has been undertaken in order to inform policy guidance through developing a better understanding of the soil C stock and greenhouse gas implications of forestry on peaty soils in Scotland. Findings suggest that disturbance from forestry activities on peaty soils could result in increased soil C loss, which could significantly reduce the net C uptake of the site and the wider net GHG emissions abatement benefits of forestry. However, recent detailed chronosequence study on peaty gley soils under Sitka spruce in Kielder forest has suggested that on peaty gleys the carbon lost through leaching, oxidation and decomposition from peat layers due to the disturbance of afforestation could be compensated for by the C accumulation in organic top layer. The overall influence of conifer afforestation on organo mineral soils carbon stocks is neutral over the time span of two rotations.
Afforestation on deep peats
On deep peats – defined here as soil exceeding their peat layer more than 50 cm, current guidance does not allow new forest establishment. Deep peat occupies approximately a quarter of the national forest estate with about 60% of this area has been afforested. Deep peat areas are a significant and growing part of the restocking portfolio. Research indicates that a negative net greenhouse gas balance may occur from restocking on deep peats where tree growth is poor, even if there is no significant soil disturbance from cultivation. The research concluded that to generate a positive greenhouse gas balance on restock sites there should be a good rate of tree growth achieved without significant cultivation. Where this isn’t possible, the site should not have a conventional (like-for-like) second rotation and may be considered for other management or restoration options.
Information is available on our research and guidance into afforestation impacts on deep peats in Wales and Scotland.
Funding & Partners
- Corporate Forestry Support (SFC)
- Forestry Commission Scotland
- Natural Resources Wales
- James Hutton Institute
- Cranfield University