Willow trees cultivated for ‘green’ energy can yield up to five-times more bio-fuel if they grow diagonally (rather than vertically). This effect had been observed in the wild and in plantations around the UK, but scientists were previously unable to explain why some willows produced more bio-fuel than others.

Now, researchers at Imperial College London have identified a genetic trait that is activated in some trees when they sense they are at an angle, such as where they are blown sideways in windy conditions. It creates more sugar molecules in an attempt to straighten the plant, and these high-energy sugars can be converted into bio-fuel when the trees are harvested.

The study was led by Dr Nicholas Brereton and Dr Michael Ray of Imperial College London. Working with colleagues at Rothamsted Research (Harpenden) and the University of the Highlands and Islands, they conducted a trial in controlled laboratory conditions on a roof-top at Imperial's South Kensington campus. They cultivated some willows
at an angle of 45deg and then looked for any genetic differences between these plants and willows allowed to grow straight upwards.

The team then looked for the same effect with willows growing in natural conditions on Orkney, which are bent over at severe angles by the prevailing wind. Their measurements confirmed that the willows on Orkney could produce five-times more sugar than identical trees grown in more sheltered conditions at Rothamsted Research in the south of
the UK.