Road Verge Biomass Harvesting

In order to maintain a road network that is safe for all who use it, verges are best managed as grassland which is cut to maintain visibility at junctions and on bends and to maintain a safe pull-over zone. Allowing shrubs and trees to colonise verges would compromise safety.

Roadside grassland represents an important opportunity for wildlife. We have lost over 97% of our wildflower-rich grassland since the 1930s due largely to the intensification of agriculture. What is left is limited mostly to nature reserves which are disconnected from one another.

Road verges can act not only as refuges for wildlife in intensively farmed countryside but can also function as corridors which enable wildlife to move through our landscape as it needs to in order to survive. ‘Nature Recovery Networks’ are what our national wildlife needs now and in the future in order to be resilient in the face of the pressures we put on nature, including climate change.

Since 1960, the Lincolnshire Wildlife Trust has worked in partnership with local authorities to identify and conserve wildflower-rich road verges across Lincolnshire. Today it manages 80km of Roadside Nature Reserves including some legally protected stretches (SSSIs) amounting to 50ha of land with a maintenance budget provided by Lincolnshire County Council and Natural England.

Between 2009 and 2016 the Lincolnshire Wildlife Trust ran a citizen science project called ‘Life on the Verge’ which was helped by over 250 volunteers. Surveys focused on chalk and limestone areas and covered a total road length of more than 3,900km, about one third of Lincolnshire’s road network. The data collected led to the designation of 159 additional Local Wildlife Sites along more than 250km of road, constituting nearly 100ha of wildflower-rich habitat.

Although Local Wildlife Sites are not protected by law they are nevertheless a material consideration in planning policy. The vast majority of these additional discoveries and designations are not managed favourably for wildlife and continue to decline in biodiversity year on year. We realised we had to find a way to manage more verges to benefit wildlife.

Our surveys have found that most verges are cut either too frequently (more than twice per year) or too infrequently. Mowing too frequently does not allow plants to set seed or invertebrates to complete their lifecycles undisturbed. When verges are cut, the cuttings are left on the verge which causes two problems. Firstly, the mulch of cuttings is a physical barrier to growth for all but the most vigorous plants. Secondly, rotting cuttings allow fertility to accumulate in the soil. Higher fertility means that only a minority of competitive plants prosper at the expense of the others which are outcompeted. Surplus fertility has accumulated in our environment due to modern agriculture.

The best way to conserve and encourage wildlife in grassland habitat is to graze it with livestock or cut it for hay. Livestock would clearly be a roadside hazard, so hay cutting has been the method of choice on as many wildflower stretches as resources allow.  

Wildflower-rich grassland which supports a range of wildlife would have been present in our natural environment before man manipulated the landscape. If left alone, grassy, open habitat will first be colonised by low-growing bushes and then by taller growing trees in a process of natural succession. 

It was the browsing and grazing by the prehistoric ancestors of our modern day livestock which allowed grassland wildlife to thrive between woodland areas. Livestock grazing and hay making can be modern day substitutes for this ancient grazing and enable our meadow wildflowers to thrive.

Hay-making requires multiple passes with machinery to cut, rake, bale and collect the cuttings so is expensive and time consuming. It is also vulnerable to bad weather because hay needs to be cut and dried in warm sunshine before baling.

There is a much smaller demand for hay to feed livestock now than in the past because other forms of feed are now grown including silage and forage crops. Furthermore, many farmers are reluctant to risk hay-making in a roadside environment where they may encounter litter which can contaminate the hay crop and damage hay making equipment.

All of these reasons make roadside haymaking less worthwhile from a farming perspective and where they were cut for hay in the past, most verges are now either left uncut or simply flailed. Only the most wildlife-rich verges are still maintained with hay cuts to preserve their conservation value but this is not viable beyond the most valuable stretches.

A suction flail harvester can cut and collect cuttings in a single pass and transport them to a silage clamp. Once collected, the biomass can be fed into an anaerobic digester (AD) facility where it is broken down by bacteria to produce both heat and biomethane. The heat can be utilised on site by the AD facility itself and nearby buildings can be heated too. The biomethane can either be burned to drive a turbine which generates electricity which can be sold to the National Grid; or it can be collected, compressed and used as fuel for vehicles and machinery such as the biomass harvester itself.

The material that remains after the AD process is called the digestate. This is a good soil improver and can be spread to land with the appropriate licence. Biomass from verges can substitute for up to 30% of AD feedstock which would otherwise be grown on agricultural land. This means we can return land to food production which has higher profit margins.

Using 30% biomass feedstock from road verges and marginal land in an on-farm 500kW AD plant can benefit a farm business by over £50,000 annually. This means that the operational costs of maintaining our road verges could be offset significantly and effectively conservation pays for itself.

Besides benefiting biodiversity, we would expect verge biomass harvesting to provide benefits in the following ways:

• Jobs will be created in remote rural locations.
• Farm businesses could diversify.
• Water quality – rotting vegetation is removed and nitrates levels are lowered in drainage water.
• Flood risk management – vegetation is prevented from overgrowing and blocking drainage channels and deeper rooting plants make soil more permeable during peak rainfall events.
• Pollination service – the work of wild pollinating insects adds £510 million to the UK’s annual crop production; wildflowers support our pollinators by providing continuity of pollen and nectar supply when crops are not in flower.
• Road user well-being – it is well documented that more attractive road verges lower driver stress levels.
• Nature tourism – verges are the countryside we see and if they are more attractive they will attract more tourism and longer stays in rural areas; cycling, walking and touring will all benefit the local economy away from principal towns.
• A more attractive countryside and transport routes will encourage people to adopt healthier habits and to take regular exercise which will deliver important benefits for our physical health and mental wellbeing.
• Local authorities will be better able to keep to Government targets by restoring and maintaining favourable condition for their roadside Local Wildlife Sites.
• Local authorities and their contractors on roadsides will be better able to keep to their ‘Biodiversity Duties’ under the Natural Environment and Rural Communities’ Act 2006.
• Local authorities will have a new way of offsetting and lowering their carbon footprint by producing green energy.
• The country’s capacity for food production will be improved due to the reduced demand for energy crops.
• Based on recent revisions of the National Planning and Policy Framework and the Spring Statement from HM’s Treasury there is a clear intention to mandate ‘Biodiversity Net Gain’ in development. This will help towards delivering net gain for wildlife as part of delivering a standard or enhanced public service.
• DEFRA’s 25 Year Environment Plan sets the target of creating and/or restoring  500,000ha of landscape for the benefit of wildlife outside of the existing nature conservation designations. By making affordable changes to road verge management on a national scale, the UK could achieve as much as 40% of that target while at the same time connecting wildlife across our national landscape for future resilience.

Roadside rubbish has been studied by the project. It is mainly plastic bottles, drinks cans and fast food packaging and it is clustered in certain locations. There is also an historic accumulation of litter that dates back several years. Litter collection is typically the responsibility of district councils.

There are ways of filtering litter as it is fed into an AD plant. Work is also underway to trial the use of a different working head on the harvester which would collect litter following a harvest.  Material collected in this way would not only make verges cleaner and remove plastic from the environment but potentially generate another source of income via recycling.

Laboratories at the University of Leeds have tested samples from a range of roadside cuttings. Potential contaminants such as poly-aromatic hydrocarbons and heavy metals have not been detected above levels that would cause concern either for anaerobic digestion or for spreading the digestate onto arable land.

The recent report from PlantLife UK entitled ‘We need to talk about Nitrogen’ explains how long term studies across our countryside have revealed that our soils are accumulating unnaturally high levels of fertility. 

Marginal land and nature reserves are receiving fertility year on year even where fertiliser is not applied because the surplus from agriculture enters and spreads through our environment. Vehicle exhaust is also a source of Nitrogen.

If we harvest biomass from marginal land including verges we are effectively making use of wasted fertility and we stand a chance of reducing levels that will restore plant diversity and therefore the greater biodiversity they can support.

An 18-year study in Cambridgeshire found that repeated cutting and collecting of hay did not significantly reduce fertility or productivity. Any loss of fertility can take a long time and appears to depend upon soil type.

A more important effect on grassland biodiversity than the loss of fertility appears to be the maintenance of the right level of disturbance from cutting and collecting cuttings.  Future studies will help us to understand how sustained biomass harvesting with no inputs can affect the quantity and quality of road verge biomass over the long term.

The height of plants is managed by cutting twice per year and is expected to decrease year on year as species composition changes and existing plants regrow to a lower height.

When we grow crops and plants in our gardens fertile soil is a good thing, but we must not forget that wild plants have evolved over millions of years to grow under natural conditions were fertility is much lower.

Only a minority of plants can thrive in high fertility because they evolved to grow in naturally fertile conditions such as flood plains. These plants can make use of the extra fertility in soil to grow and reproduce more quickly and so outcompete all other species.  This leads to a drop in biodiversity and the same plants growing everywhere so that our countryside looks the same wherever we drive.

By using biomethane we are utilising short-term cycled carbon that has been fixed by photosynthesis in green, growing plants in the same year. We are avoiding using fossil carbon – so we are not adding to the CO₂ in the atmosphere.

By using anaerobic digesters instead of cattle we are capturing nearly all the methane which then cannot act as a greenhouse gas. Fugitive emissions of methane from an AD facility are just the same as from a standard silage clamp.

Biomethane can be used to substitute for the diesel that powers the AD plant and the biomass harvester making the use of energy circular and more sustainable. There is a growing market in haulage companies for the consumption of biomethane-sourced compressed natural gas (CNG). CO₂ emissions from freight transport on our roads could be reduced significantly. Currently haulage companies are already reporting 60% reduction in carbon footprint from using a CNG/diesel fuel mix.

Although this is not the best way to manage grassland for wildlife, it is much better than a ‘no change’ scenario where we are seeing a continual decline in roadside grassland wildlife. This practice would be excluded from the best verges that account for up to 1% of the network where hay-making would continue.

Surveys in Lincolnshire have shown that the next best c.10% of verges offer significant biodiversity opportunity and are restorable if suction flailed with careful practice. The biodiversity on the remaining c.90% would benefit from suction flail harvesting twice per year. This large majority of resource helps to build a business case for harvesting road verge biomass and makes the conservation of the whole network possible.

• Research is currently underway to investigate the use of AD digestate as a peat substitute in horticulture. This will save our peat bog habitat which is an important ongoing carbon sink and prevent carbon captured for the long term in our peat being released into the environment.
• As has been achieved with wood fibre in both Sweden and Norway, bio-refining of cellulose from grass cuttings could be developed to create substitutes for plastic in our packaging and clothing.
• Studies have already succeeded in creating aviation fuel from biomass.  We might even be able to reduce the carbon footprint of a major cause of climate change – flying.

Grassland management always looks very destructive. We can choose when to cut and how often. Naturally, wild herbivores would graze lightly and inconsistently leaving some areas less disturbed than others. This would allow some wildflowers to remain and set seed.

It’s also important to realise that most grassland wildflowers are perennial which means they live for several years and often reproduce without the need to set seed by creeping and spreading. Cutting and clearing the cuttings will allow perennial wildflowers to regrow and re-flower while reducing the vigour of more competitive species that would otherwise overtop them.

All plants have a value for wildlife. Unfortunately, abandoning verges is not the same as leaving them to nature because our soils are now unnaturally fertile and we have removed many natural grazers from the ecosystem. This means that without cutting and clearing cuttings, the minority of tallest and fastest growing species which thrive in more fertile conditions would take over. This would lead to a net biodiversity loss and all verges would look the same.

Ultimately, if never cut, grassland on verges would develop into woodland. Aside from causing a hazard to road users, this would represent a loss of much of our remaining wildflower grassland which is recognised as a vital resource for pollinators with its own suite of wildlife that adds biodiversity to our ecosystem. 

Restricting cutting times to May and August allows perennial wildflowers to regrow and re-flower and for invertebrates to recolonise. Although it does disrupt wildlife temporarily it sustains it in the long term.

The status quo (insufficient cutting, cutting too frequently, cutting and leaving a mulch) is leading to the loss of grassland wildlife as coarser grass species, taller herbs and scrub take over. These other species can be maintained in our woodlands, woodland edges and hedgerows adding their own biodiversity.

Finding a way now to maintain species-rich grassland that is self-sustaining throws a lifeline to a nationwide habitat network that would otherwise be lost.

The peak activity of invertebrates is in June and July which can be avoided. However, cutting at any time will result in some loss of invertebrates and seed. This can be mitigated by leaving sanctuary strips on wider verges at the base of hedgerows and cutting a road verge network on rotation. Alternating sides when cutting can help in more sensitive areas. The basic principle is not to cut everything everywhere at once but to allow some cover to persist.

Our extensive surveys of the county’s road verge wildlife have been recorded on Geographic Information Systems which we can refer to. We can use these to target more sensitive management where there is higher biodiversity risk.

We have found recently published scientific literature which shows that two cuts per year is best for both biodiversity and energy recovery. This means that to a large extent, road verge biomass harvesting can be self-regulating.

Cutting more frequently only achieves diminishing returns so would not be worthwhile.  We would just need to ensure as we do currently that the more sensitive verges are managed appropriately.

The best verges would act as sources of wildlife for the rest and could even be harvested for green hay to seed restorations in key locations. Equally vital, is that this is seen as an opportunity to gain a rewarding energy yield in return for minimal inputs.

This model has to be made a central theme both ecologically and economically – so no herbicides or fertiliser or mechanical cultivation for soil improvement would be required.  This makes sense in terms of optimising your ‘energy returned over energy invested.’ Effectively, biomass harvesting businesses would be harvesting an asset which is ‘mopping up’ the leftovers of fertility that would otherwise be wasted from farming operations. Yes there is a risk of a ‘Pandora’s Box’ effect – but this is mitigated when it wouldn’t make business sense. The ‘do nothing’ scenario means we will lose this habitat anyway.

The suction flail design allows the side-arm flail to be carried above ground level when cutting the back verge which would pass over small vertebrates. Birds rarely nest on road verges and if they do they will be well back towards a hedgerow on the broadest verges. Guidance will ask for these to be left as sanctuary strips. If we don’t cut at all we will lose their habitat.

Mowing could be restricted to July/August in certain stretches where e.g. cowslip is a local feature. In more species rich verges, one cut per year is often sufficient. Hedgerow bases will still provide a refuge for spring flowers. In conjunction with appropriate hedgerow management (i.e. cutting every three years rather than every year) both spring and summer nectar and pollen supply can be sustained.