Nature-lovers have been urged to watch their local woodlands for early spring bluebells – and help experts assess the effects of Britain's topsy-turvy weather on native flowers.

Bluebells have flowered early this year after a warm winter, with almost twice as many sightings reported as at the same time in 2011, when the average flowering date was April 12.

But experts are keen to understand how the short, sharp cold spell in early February is affecting flowering dates and locations.

The Woodland Trust, in partnership with the Forestry Commission, National Trust, Wildlife Trusts and the RSPB, hopes people will record their sightings on the VisitWoods website, which hosts the country's largest online database of bluebell woods.

Norfolk has 19 woods flagged as being bluebell hotspots, including Bure Marshes near North Walsham, Foxley Wood, Blickling estate near Aylsham, Pretty Corner Wood near Sheringham, and the Norfolk Wildlife Trust's Lower Wood at Ashwellthorpe, near Wymondham.

Gayle Wharton, VisitWoods project manager, said: 'The native bluebell is the quintessential British sign of spring and we need the public to visit woodlands and discover when they are appearing so we can track their arrival.'

The website allows the public to search from over 1,000 bluebell woods across the UK, and to add any that are not listed. By building up a more detailed picture of flowering dates and locations, the Woodland Trust hopes to increase the database and see how the woods are affected by changes in temperature.

?To find a bluebell wood go to VisitWoods.org.uk/bluebells.