Campaigners have warned about the environmental dangers of bioenergy, saying burning wood is not low-carbon. However, forests can – and must – be managed in a sustainable way that maintains or even increases the carbon stock, writes Tony Juniper.

Tony Juniper is co-founder of Robertsbridge. A former executive director of Friends of the Earth, he is advising Drax on its sustainability strategy. Drax is a power station in the UK that has partially converted from coal to biomass.

We need to make the transition to a zero carbon economy, and fast. Central to how we must do this are several parallel priorities – including the phase out of coal for electricity generation, the expansion of renewable energy and the conservation and expansion of forests.

When it comes to the exit from coal, cleaner alternatives must be brought forward to replace it, including wind and solar power. But although these sources of renewable energy are growing rapidly, they still come with challenges, especially because wind is becalmed on still days and solar ceases to generate at night. This intermittency can be addressed via the use of electricity storage technologies, or through other clean power sources to back them up when needed.

Hydropower is a tried and tested source of more controllable clean electricity, but there are relatively few European countries with the geography required for making a major contribution to national supply. Tidal power is predictable and some countries (such as the UK) have an opportunity to generate significant power from this source. It will, however, be limited by the number of suitable sites and although still in its infancy is already attracting opposition from some conservation groups. Nuclear power is low carbon but inflexible and its constant output not suited for working with intermittent wind and solar, which require more responsive low carbon back up.

When it comes to electricity storage, battery technology is leaping forward, driven in large part by the shift toward electric vehicles. Grid-scale batteries are, however, expensive and the huge cost of sufficient capacity to back up a run of dull calm days at present challenges economic and political viability. Electric cars are on the rise, offering some potential to balance the grid contribution of intermittent renewables with stored power, but in the short-term this is more likely to be another source of increased demand for clean power, rather than an immediately available means for balancing supply with use.

Another source of highly controllable renewable power that can be turned up and down at short notice – and which indeed is a storage option at the same time – is biomass, including wood pellets. In common with nearly every other source of electricity it has proved controversial, including at Britain’s largest power station – Drax. Drax was built to generate electricity from coal but has as part of the UK’s low carbon strategy partially converted to using wood pellets.

EU probes UK aid to convert huge coal power plant to biomass The EU launched an investigation on Tuesday (5 January) into whether British government aid to convert the giant Drax power station from coal to more environmentally-friendly biomass breaches the bloc’s state aid rules.

Campaigners have said that the switch to wood brings environmental dangers and is not low carbon, but having just spent time in the United States looking at the supply chain in wood pellets for Drax, I believe it to be a rational energy choice, so long as basic sustainability conditions are met. For example, forests from which biomass is derived must be managed in a way that maintains or increases the carbon stock.

I found that the managed forest landscapes of the US South (more than three times the size of the UK) produce about sixth of the world’s wood. There are thousands of forest owners there – from global companies to small family holdings – the majority of whom keep their forests producing wood for economic reasons. If there is a market to supply, they put time and money into forest management. If there is less economic incentive, then forest owners told me that stands of trees are more likely to be converted to other uses, such as urban areas or solar farms. Strong demand for wood is the main reason why since the 1950s the volume of carbon stored in standing timber in the forests of the US South has increased by over 100%.

From a climate change perspective this increase is to be welcomed, and so are economic signals that maintain or even strengthen that dynamic. This is especially the case when in some US forested landscapes from where a great deal of European wood pellet fuel comes there has been a recent drop in demand for wood from some traditional sectors. I saw pulp mills that had closed because of a switch from newspapers to smart phones and a plywood plant that fell victim to a slow down in house building following the 2008 financial crash.

In addition to taking thinnings from forests managed to produce high-value saw timber, a lot of the material going into the wood pellet mills that I visited were branches and other wood left on the ground after the harvest of trees for sawmills. Sawmill waste was also being shipped in. I heard that forest owners get about three times as much money if they send their trees to sawmills rather than wood pellet plants, so very little high grade timber finishes up being made into fuel.

While most of the forests of the US South have been managed for wood for centuries, and even though most of the highest conservation value forests that remain have been protected, I heard of claims that the wood pellet industry is destroying old growth forests. I visited a claimed case in point in North Carolina but found it had been clear-cut on several occasions during the last 100 years. And although it had been harvested two years previously it was vigorously regenerating, part of a mosaic of mixed age forest that was evidently beneficial to wildlife.

That mosaic was a reminder that when it comes to the pros and cons of wood fuel that it is necessary to look at the whole landscape, rather than any particular plot of forest, let alone individual trees. If we can raise our sights to do that, then from a wildlife and carbon point of view it becomes clear that a sustainable wood pellet industry can indeed be compatible not only with environmental goals, but also a complex economic landscape where jobs and income most powerfully determine how the land is used.

If we really do wish to phase out coal, expand renewables and maintain and increase the area of forests, then wood fuel can play a part. It’s all about finding the best ways of joining the dots.