Environmental Stewardship and climate change mitigation (TIN107)

Summary by option group

Boundary options and capital payments

Payments to restore hedgerows, and increase hedgerow tree numbers, help to increase carbon stored in plants. Currently hedgerow tree replacement is not matching the rate of loss and the population of hedgerow trees continues to decline. The ES options and capital items that encourage hedgerows and hedgerow trees have no impact on agricultural production, and therefore, the associated carbon gains are displacement-free.

Hedge restoration, combined with an associated increasing diversity of hedge structure, will increase the variability within the hedgerow habitats and this should help the natural environment adapt to climate change. The additional cover provided by taller hedges and hedgerow trees will also help farming adapt to increasing risks of wind erosion in drier periods and provide shade for livestock on hotter days.

Tree and woodland options

Woodland restoration and woodland fencing are considered to increase carbon storage in vegetation by the removal of grazing pressure allowing an increase in woodland biomass. New woodland edges not only reduce emission by stopping cultivation on arable land they also increase soil and vegetative carbon.

New oak woodlands are estimated to sequester 14.67 t CO2e/ha/yr2 in the biomass during the development phase, in addition to gains in soil carbon (FC, 2003). The Read Report (Read et al, 2009) recommended ambitious targets for tree planting and woodland creation in the UK, to ensure that full potential of trees in combating climate change are realised. Pro-actively seeking opportunities to use HLS woodland creation options can help ensure that ES contributes to this target.

Where the carbon benefits associated with woodland planting come at a cost to agricultural production, they must be seen as an additional benefit to the primary (biodiversity, landscape or other) objective of the planting design. These primary objectives can include adaptation to future climate change, for example by planting trees to intercept run-off and hence adapt to the anticipated increase in heavier rainfall events.

Areas where tree planting need not conflict with agricultural production are the restoration of orchards and wood pasture. Permanent crops have the advantage of combining carbon storage (in both soil and vegetation) with agricultural production.

One study found that soils in the top 30cm in a traditional orchard contained 74 t C/ha compared to 26-34 t C/ha in arable soils. In addition, the orchard included 21.4t C/ha in the trees and above ground roots alone. (Robertson et al, quoted in Natural England, 2012).

Historic environment options

ED2 arable reversion to protect historic features will have similar mitigation benefits to other arable reversion options (see Table 2).

Minimum tillage (ED3) is considered to reduce emissions, by reducing fuel consumption during cultivations, and to achieve small increases in soil carbon. By allowing production to continue these benefits are considered to be free of displacement.

Crop establishment by direct drilling (HD6), will achieve similar mitigation benefits to ED3; indeed it is likely that soil carbon gains will be greater owing to the reduced level of soil disturbance. For both options however the risks are soil compaction (which would lead to an increased level of N2O emissions) and an increased need for herbicide application (with emissions from fuel use). The actual level of mitigation benefit achieved will depend on whether or not compaction and/or weed management become a requirement at the specific location.

The management of archaeological features on grassland (ED5) is assumed to reduce emissions through a reduction in farm operations on the feature. Soil carbon gains can be assumed where the land is taken out of arable cultivation.

The impact of traditional water meadow restoration is particularly dependent on the baseline conditions. Significant gains of soil organic carbon can be expected where the habitat is restored from semi-improved or improved grassland. On the other hand, restoration from neglected sites (un-drained, scrubby) is likely to be more neutral or may even have a small increase in greenhouse gas emissions.

Buffer strips

The introduction of buffer strips will increase soil carbon by preventing the oxidation associated with continued cultivations and will reduce GHG emissions by reducing machinery usage and fertiliser applications. Hence they are considered as having significant potential for climate change mitigation. The GHG Action Plan notes that buffer strips on 'compacted wet headlands offer potential GHG mitigation and carbon sinks'. This could apply also to field corners (EF1, EK1) or in-field grass areas (EJ5).

By protecting valuable features from the impact of farming operations and by providing additional habitat structure across the landscape, buffer strips can also make a contribution to climate change adaptation.

Arable options

The field corner option (EF1) can achieve mitigation and adaptation benefits in the same was as buffer strips.

Wild bird seed (EF2, HF12) and nectar mix (EF4) options are assumed to achieve emissions reduction through the reduction in fertiliser and pesticide inputs, compared to the prior management. A reduction in cultivations, due to re-establishment every 2 years, should aslo reduce emissions associated with cultivations. On arable land there may be some gains in soil carbon.

Beetle banks (EF7) are believed to increase carbon sequestration in the soil forming the bank. Whilst there is an area of land taken out of production, the bank can be viewed as an investment in the productive capacity of the remainder of the field, by providing a habitat for predatory beetles and spiders which will help reduce aphids in wheat, hence minimising or potentially nullifying completely any overall impact on production levels. Beetle banks in the correct location can also help reduce soil erosion and associated sediment and soil carbon losses.

Options for arable headlands (EF10, EF11, EF13, HF16-20) can achieve emissions reduction where there is a reduction in fertiliser and other applications. The presence of bare ground and relative lack of vegetation may have a small and short term negative impact on soil carbon, although the overall greenhouse gas balance will normally be better than under the previous management.

Under Under-sown spring cereals (EG1) are understood to achieve significant reductions in emissions on a per hectare basis where this replaces a winter sown crop and where clover is included in the under-sown crop. The mitigation benefits are accrued through the protection of soil from erosion (as with winter cover crops) and a reduction in the inorganic, nitrogen based, fertiliser requirement where the under-sown clover is retained in a clover-ley throughout the following year.

Resource protection options

As a general rule options that prevent soil erosion will also prevent the loss of carbon embedded in the soil, although the ultimate fate of soil carbnon in the event of soil erosion will depend on whether the eroded soil is deposited on land or in water (Warner, 2011).

Maize management options (EJ2 and EJ10) are considered to help with mitigation by reducing the loss of soil organic carbon through soil erosion. In addition, where clover is used in the under-sown crop (an optional element for both options) and it is retained as a clover-ley though the follwing year, there will be a reduction in emissions associated with a reduced need for inorganic nitrogen fertilisers.

Winter cover crops (EJ13) protect soil organic matter from loss through erosion, by providing ground cover throughout winter. They are also understood to reduce N2O emissions (by reducing NO3 leaching) and incorporate additional biomass into the soil (Warner, 2011). ADAS (2009), estimate that it is the protection from erosion that is the most significant impact and hence the options will be most valuable for climate change mitigation on soils prone to erosion.

Permanent grassland

Permanent low input grassland that has been managed as such for many years will have higher levels of soil carbon than arable land (see Table 3). Maintaining the land without cultivations is essential to protect the carbon store. Whilst the low input grassland options (EK3, EL3) do not appear to have significant impact on greenhouse gas emissions (because of the assumption that the land is already in low input management), they will be important in protecting the carbon store.

Recent research suggest that restoration of species-rich grassland (for example, HK7, HK8) can have significant benefits for carbon sequestration in the soil. Introduction of red clover and the cessation of NPK fertiliser application were identified as the most relevant practices for promoting carbon sequestration. However, the greatest impact was achieved by a combination of red clover, cessation of fertiliser applications and the addition of seed mixes (to increase species diversity) (De Deyn et al, 2011).

Compaction of long-term permanent grassland is understood to be a widespread issue. Relieving compaction improves soil aeration and is likely to decrease direct N2O emissions (Newell Price et al, 2011) becasue roots can penetrate deeper into the soil, facilitating increased nutrient uptake.

One issue of particular significance for agri-environment is the continuation of grasland management on land reverted from arable under a former agreement (for example, CSS or ESA Arable reversion). ADAS (2009) suggest that arable reversion to permanent grassland sequesters soil carbon at a rate of between 1.9 - 7t CO2e/ha/yr, depending on:

  • soil type;
  • previous land use;
  • climate; and
  • grassland management practices.

Hence we can estimate that arable reversion under the classic shemes (Countryside Stewardship / Environmentally Sensitive Areas) sequesters carbon at a rate of 164 - 604k tCO2e each year.

The process of carbon accumulation will continue for decades (although the rate of accumulation will decline), beyond the life of the initial agri-environment agreement. Therefore, at the expiry of the original agreement, it is important that the land is maintained as permanent grassland, both to hold on to the carbon already captured and to realise the full potential of the reversion to capture additional carbon.

Maintaining former reversion sites as grassland does not involve any new management change and is therefore free of displacement risk.

Looking into the future, the Climate Change Committee (2011) notes that many grassland soils have reached their maximum carbon carrying potential (they are 'carbon saturated') and their ability to hold on to that carbon may be threatened by climate change. New management practices that enables soils to hold on to carbon in warmer, drier conditions and during periods of increased run-off risk may be required.

Peatland restoration

Peatland restoration is a priority for climate chage mitigation through ES, owing to the carbon-rich nature of peat soils (see Table 3) and their vulnerability to loss by erosion.

That vulnerability of the carbon in peat soils is increased significantly when the soils are damaged, including by drainage, cultivation and loss of vegetation cover. Hence, ES achieves mitigation benefits by re-vegetating and re-wetting peat soils to prevent further carbon loss. Beyond preventing further loss of the carbon embedded in peat soils, ES can help to create the conditions for active peat formation. HLS options that create and restore peatland habitats (for example, HQ8, HL10) have the greatest impact of all ES options on a per hectare basis.

The presence of sphagnum is considered to be an indicator of carbon sequestration through active peat formation and hence restoration projects should aim to increase the area of sphagnum. However, in the lowlands, sphagnum will only normally (re)establish on rain-fed (ombotrophic) mires.

Sphagnum lawn with sundews

The restoration of peatlands, whether in the uplands or the lowlands has significant co-benefits with resource protection and biodiversity, hence providing a win-win situtaion both for climate change mitigation and for adaptation. Lindsay (2010) provides a detailed assessment of peatland restoration techniques, including an assessment of the potential impact of climate change on peatland habitats.

In the lowland situation there is a significant potential for displacement of production, where drained peat soils used for productive farming but emitting significant amounts of carbon restored to protect their carbon content. Where land managers are willing to restore lowland peatlands, for carbon or other environmental reasons, ES provides an effective mechanism for securing and rewarding that commitment.

Heathland restoration

One ES option increases rather than decreases GHG emissions (Warner, 2011): HO3 Restoration of forestry areas to lowland heathland. This is because of the loss of carbon caused by the felling and non-replacement of trees. The actual scale of this impact will depend on the amount of material to be felled, the way the felling is carried out and the type of heathland. Carbon management needs to be seen in the wider context of environmental management and the restoration of any heathland under HLS should be consistent with Forestry Commission (2010) policy on When to convert woods and forests to open habitat. Carbon emissions from restoring heathland can be reduced by:

  • Retaining a low rate of tree cover, particularly where this is consistent with providing a varied habitat structure or buffering the site.
  • Use of the timber as forestry products or for woodfuel.
  • Adopting a gradual felling programme, particularly where this is linked to the 2 points above.
  • Minimisation of soil disturbance during restoration.

It should also be noted that that heathland restoration from arable and ex-mineral extraction soils will result in net carbon sequestration, because of the high carbon content of heathland soils.

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