This report examines the potential of nature-based solutions to contribute to Scotland’s net-zero emissions target.

Scotland is facing the twin challenges of a climate emergency and biodiversity crisis. Changing the way we use the land and sea is now essential to both store carbon and help society adapt to climate change. Doing so can also help to improve the state of nature, which is experiencing unprecedented threats. 

Nature-based solutions feature prominently in the global biodiversity agenda. Vegetation growth and healthy soils, as well as sea floor integrity, provide a crucial way of locking away carbon emissions. However, it is the additional multiple benefits unique to nature-based solutions – addressing biodiversity loss, and adaptation to locked-in climate change – that makes them such a crucial part of a net-zero strategy. These are widely regarded as ‘no-regret’ actions to address climate change, but the evidence base to support their direct impact is complex. As such, further work is required to understand their practical application in Scottish circumstances.

This study assesses evidence for the greenhouse gas (GHG) mitigation potential of four nature-based solutions in Scotland (agroforestry, hedgerows, un-cultivated riparian buffer zones and the restoration of species-rich grasslands) and how these can help mitigate the impacts of climate change and reduce biodiversity loss. In addition, we provide a synthesis of the strength of evidence for including these as part of net-zero policy objectives and carbon codes.

The Land Capability for Agriculture (LCA) classification for Scotland has been used since the 1980s to inform decision-making on land use management, planning and valuation.

This report explores the potential for a new research tool to estimate land capability under future climatic conditions – the Land Capability of Scotland research platform. Development in this project has been based on the original LCA guidelines. The platform is a set of computing tools (not PC based) for data integration, calculation, analysis, mapping and visualisation, allowing models to be run to estimate land capability constraints and generate digital maps.

The Land Capability research platform is designed to be a ‘risk and opportunities assessment’ tool operated by researchers; the Land Capability of Scotland research platform does not replace the existing published LCA classifications.

The platform has initially been developed to produce estimates of Land Capability for Agriculture under different climate change projections and has further potential to support research on a broad range of land uses and benefits, such as forestry and ecosystem services.

Results

• The original LCA guide has been successfully coded and computing structures implemented, integrating multiple spatial data sets and modelling tools to estimate the individual constraints that determine the LCA and its overall classification.
• A key challenge is the ability to model soil water balance appropriately. A soil water balance model was implemented within the platform, but further work is required to better calibrate the model and validate the estimates. 
• Initial analysis between two baseline periods indicates that climate change has already altered land capability and is likely to further impact it in both positive and negative ways in the future. 
• Reduced water availability is likely to be a key determining factor. Initial analysis suggests that soils, especially those with a low water holding capacity, are likely to become drier and with greater frequency. 
• This implies an increased risk of crops, grassland and vegetation experiencing difficulties in accessing water. The LCA and constraint maps indicate where this may occur.
• There is a substantial risk that land currently classed as prime agricultural land (classes 1 – 3.1) may experience reduced production capability due to dry soils in an increasing number of years with drought conditions.
• Conversely, potentially areas such as the north-west Highlands may experience increased precipitation totals in some years, meaning soils there becoming wetter.
• There is likely to be increased annual variability in land capability associated with increasing climatic variability and extreme events, such as wet seasons or years followed by dry ones.
• The platform development has been a ‘learning by doing’ iterative process, and further improvements are possible. The research platform will continue to be used and developed in the Scottish Government’s 2022-2027 Strategic Research Programme.
  

Monitoring soil health in a changing climate is a priority for the Scottish Government.

In 2020, CXC published a baseline report that pulled together existing research on the vulnerability of Scottish soils to climate change. The report found that, while Scotland has a significant knowledge base on soils, there was no single indicator that could be applied to all soils, climatic conditions or land uses.

This scoping study takes the 13 potential indicators the baseline report identified and considers their strategic relevance to monitoring soil health in the context of existing land use Scotland. 

Key points

• Potential primary soil health indicators were identified for several land use categories.
• However, it is not possible to identify a single, definitive indicator for each individual land use category and suitable indicators were not identified for several categories such as Urban or Amenity soils.
• Seven indicators were considered extremely important for more than 50% of the categories assessed:
     o soil organic matter content
     o topsoil depth
     o erosion features
     o bulk density
     o bacteria and archaeal diversity (DNA methods)
     o fungal and nematode diversity (DNA methods)
• Visual assessment of soils, moisture content and dissolved organic matter were considered extremely important for the fewest categories, though moisture content was considered the primary indicator for transport infrastructure.

The issue of dependency between indicators generates a layer of complexity that requires further exploration.

Monitoring soil health in a changing climate is a priority for the Scottish Government.

In 2020, CXC published a baseline report that pulled together existing research on the vulnerability of Scottish soils to climate change. The report found that, while Scotland has a significant knowledge base on soils, there was no single indicator that could be applied to all soils, climatic conditions or land uses.

This scoping study takes the 13 potential indicators the baseline report identified and considers their strategic relevance to monitoring soil health in the context of existing land use Scotland. 

Key points

• Potential primary soil health indicators were identified for several land use categories.
• However, it is not possible to identify a single, definitive indicator for each individual land use category and suitable indicators were not identified for several categories such as Urban or Amenity soils.
• Seven indicators were considered extremely important for more than 50% of the categories assessed:
     o soil organic matter content
     o topsoil depth
     o erosion features
     o bulk density
     o bacteria and archaeal diversity (DNA methods)
     o fungal and nematode diversity (DNA methods)
• Visual assessment of soils, moisture content and dissolved organic matter were considered extremely important for the fewest categories, though moisture content was considered the primary indicator for transport infrastructure.

The issue of dependency between indicators generates a layer of complexity that requires further exploration.

This project set out to review the current state of knowledge on the potential for carbon sequestration in key Scottish upland open habitats. Upland soils play a vital role in regulating greenhouse gas (GHG) emissions in our environment. Scotland’s soils contain 2500-3500 Mt of carbon, much of which is located in upland soil environments. This is equivalent to more than 200 years of Scotland’s annual greenhouse gas emissions. The management of uplands and their soils will therefore be critical to achieving Scotland’s ambitious net-zero emissions target.

Despite the well-known potential of soils to store carbon, however, there is uncertainty as to the long-term stability of this carbon pool. Increasing temperatures, altered patterns of rainfall distribution, and changes in land use all influence this process and threaten to reduce soil carbon stocks.

This review identifies the key drivers of change and covers three upland habitats: upland dry heath, upland wet heath and upland grasslands, defined by vegetation communities. It assesses potential GHG fluxes and the impact on biodiversity within these habitats.

It found very limited information regarding impacts on soil carbon stocks or GHG emissions; studies giving a full balance sheet of ecosystem stocks and flows of carbon in response to environmental or management change were particularly scarce.

Key findings include:

• Scotland’s soils contain around 2,500-3,500 Mt of soil organic carbon. The various mineral, organo-mineral and organic soils found under moorland, montane, and rough grassland contain around 45% of total Scottish soil organic carbon stock.
• Soil organic carbon accounts for 90% of the carbon stocks in these habitats. Therefore, studies which only consider changes in carbon held within the vegetation severely under-estimate changes in total carbon stocks.
• GHG emissions in open upland habitats in Scotland occur as a result of emissions of carbon dioxide, methane and nitrous oxide. 
• There is some evidence from Scotland that Molinia grasslands contain large carbon stocks within the vegetation, which are reduced by grazing.
• When upland soils are left bare after excessive grazing or burning, there is a significant increase in the risk of soil carbon loss due to erosion.
• The impacts of future climate change on carbon stocks are complex and are likely to depend on current and future management, soil type and vegetation communities. They have not been well researched in the Scottish context: this is a substantial gap in knowledge.
• The review found an important knowledge gap on the interactions of drivers on GHG emissions, carbon stocks and biodiversity.

This report was commissioned to analyse the indicators available to monitor Scotland’s soil health. Soil health is essential: the benefits range from food production to filtering water, reducing flood risk and regulating climate.

The second Scottish Climate Change Adaptation Programme (SCCAP) identifies soil health as a priority research area, following concerns over a perceived lack of data or gaps in understanding Scotland’s soils. This study summarises previous work on Scottish soils, explores existing datasets, and identifies metrics to support the monitoring of soil health and the vulnerability of Scottish soils to climate change.

 Key findings

• Scotland has a significant, world-leading soil knowledge base and a broad data resource portfolio. However, the existing evidence base does not contain tools identified as appropriate for monitoring change in Scottish soils.
• Thirteen indicators with potential to measure soil vulnerability to climate change in all soil types were identified.
• A total of 41 existing datasets that contain baseline and/or resurvey data for Scottish soils have been identified. Resampling of some of these long-term national datasets has potential to support further development of the 13 identified indicators (Table A10).
• A critical knowledge gap exists regarding the dependencies of the 13 identified indicators (i.e. factors they are reliant on), their interactions and hence whether a reduced core set of indicators could be identified at a future stage. This is compounded with critical gaps in our understanding of the interactions between soil properties. This knowledge gap has a major impact on soil biological diversity and therefore functioning of the soil system.
• No single indicator measures the full range of relevant properties encompassing all soils or climatic conditions.