大象传媒

According to Staffordshire Wildlife Trust, fish live in trees too. The Trust's biologists are using wood as a remarkably effective tool to change the depth and flow of stream s and improve them for wildlife. They don't just stop at streams either: at the confluence of the Tame and Trent rivers , they've submerged entire willow trees in gravel islands in a project to widen the river channel.

Across the country in Norfolk the National Trust has felled trees into the River Bure at its Blickling Hall estate and in just a few years, has seen gravel beds improve for trout - members of the local fishing club are impressed - and exotic damselflies.

In Nature: Wood and Water, Brett Westwood explores the growing use of coarse woody debris( CWD) in managing our rivers. Visiting the sites he finds that this natural engineering is remarkably cheap and fast-acting. Wood felled into sluggish currents can vary flow rates and affect silt deposition. In some places scouring by faster currents has exposed gravel beds which are spawning areas for trout, and slacker areas where the young trout can shelter in pools or hide among the tangle of branches. In Staffordshire, the debris has helped native crayfish to hide in shallow streams, and the wood itself is a breeding ground for rare insects including the scarce logjammer hoverfly which lays its eggs in partly submerged sunlit logs.

There are worries from landowners about flood prevention, but according to Alastair Driver of the Environment Agency, if sites are carefully chosen, then CWD could be useful for retaining water higher in river catchments and preventing excessive flooding downstream. By mimicking nature, and allowing our rivers to be more dynamic, we could improve the quality of our river wildlife and fulfil some of the ecological requirements of the EU Water Framework Directive.