Biofuel crops bring biodiversity benefits

19 March 2009 by Tom Marshall

Planting crops for biofuel could improve biodiversity in the British countryside as well as helping soften the impact of human carbon dioxide emissions, according to new research.

Harvesting biomass

Harvesting miscanthus grass

The paper, published in the Journal of Applied Ecology, suggests that crops like coppiced willow or miscanthus grass can support more wild species than traditional arable crops, particularly in the uncultivated margins around the edges of fields.

These fast-growing crops are grown to be burned in biomass power stations; because this emits only the carbon that the plants absorbed while they were growing, advocates say it could offer a long-term source of carbon-neutral energy.

And there's plenty of room for them in Britain. The UK government has been pushing for more biomass crops to wean Britain off its dependence on fossil fuels. It wants farmers to plant these crops on 1·1 million hectares of land by 2020, compared to just 7500 hectares at the moment.

That target is achievable without seriously affecting our ability to grow food, the researchers say. In all they identified 3·1 million hectares of land that would be suitable, though some of this is on lower grade agricultural land being used to grow food at present so converting all of it to biomass could cause conflict.

This potentially suitable land makes up 39 per cent of the land area of the east midlands and 17 per cent of the south-west - the former region was seen as particularly suitable because of factors like its flatter countryside and smaller areas of landscape classed as sensitive.

The crops could be mixed with traditional arable crops to provide a more varied set of wildlife habitats. "Our research suggests it could be possible to place energy crops within an arable landscape and use them as sources of biodiversity," says Dr Alison Haughton, an ecologist at Rothamsted Research and lead author of the paper.

The researchers tested 16 commercial fields of coppiced willow and 16 of miscanthus grass for biodiversity, measured using indicators like the number of butterflies found in field margins and of other plants growing in the planted area itself. They compared these results with similar measurements taken around 255 arable fields devoted to a variety of crops.

Biofuels and wildlife

They found more butterflies around both crops than around arable fields - on average 60 per cent more in the miscanthus plots, and 132 per cent more around the willow plantations.

There were some exceptions to this pattern, though - for example, butterflies of the family Pieridae, which includes species like the Small White, were less common around both biomass crops. On the other hand, butterflies of the family Satyrinae, which includes the Gatekeeper butterfly, were 370 per cent more numerous around miscanthus and a remarkable 620 per cent more numerous around willow.

Interestingly, despite the magnitude of these percentage differences, additional unpublished analyses show that the difference in total abundance of butterflies between the two biomass crops was not significant - both offer an advantage over arable crops.

Some of the unpublished evidence suggests willow might be a better bet for encouraging biodiversity in Britain than miscanthus grass - for one thing, it is a native tree rather than a type of grass from Asia, and so might be expected to support a larger community of other species.

When the abundance of broadleaf plants was counted, willow and miscanthus supported similar numbers within the crop itself immediately after planting, but the willow pulled ahead once both had become established and had many more broadleaf plants. On the other hand, there was no discernible difference in the number of grasses found in the midst of either crop.

Haughton explains that the team has done more analyses since this study to test the hypothesis that perennial weeds, which persist year after year, should become more common in plantations of willow, which is harvested every 2-3 years, than in miscanthus, which is harvested annually and so is disturbed more frequently. The tests confirmed this hypothesis; annual plants, by contrast, were found in similar numbers in both crops.

Part of these plants' biodiversity benefits may arise because they require less disturbance of the ground than most arable crops, which need annual ploughing and harvesting. This means biomass crops give wild plants and animals a more stable environment.

Sounding out the public

Another part of the study used interviews with the general public to find out their views of biomass planting and its effect on the countryside. Researchers at the University of East Anglia showed the interviewees computer visualisations of biomass crops in different situations and asked what they thought.

In general people were very supportive of biomass crops, though they tended to prefer small blocks of plantings interspersed with other crops rather than vast areas devoted to a single biomass crop. They also seemed to prefer the idea of small local power stations so that lorries of biomass don't have to travel long distances to bring the fuel to where it will be used.

There were some concerns about having a biomass power station nearby, but sensible planting can help address this - Haughton says biomass plants themselves could effectively conceal such a station. "People did have some objections but the problems aren't insurmountable - there is lots of potential to site crops to get round these issues," she explains.

She explains that the team is now planning further investigations into topics like how the distribution and diversity of annual and perennial weeds differs between arable and biomass crops, how big fields of biomass crops should be to maximise biodiversity, and whether butterflies or something else are the best indicator of biodiversity in arable and biomass crops.

Another question she hopes to investigate is how big the uncultivated margin around a field should be, and how it should be managed. Yet another is how management of the crop could be manipulated to improve the biodiversity benefits of miscanthus plantations to a level comparable with coppiced willow.

The study was a collaboration between scientists at Rothamsted Research, the University of East Anglia, the Game and Wildlife Conservation Trust, the Centre for Ecology & Hydrology and the University of Exeter.

It comes out of the £24m Rural Economy & Land Use (RELU) programme, which aims to draw together research across different disciplines to understand the social, economic, environmental and technological challenges that rural areas face.

RELU is an interdisciplinary collaboration between the Economic & Social Research Council (ESRC), the Biotechnology & Biological Sciences Research Council (EPSRC) and NERC. Additional funding comes from the Scottish Government and the Department for Environment, Food & Rural Affairs.