LONDON.- You walk by them everyday, but do you know their names? Trees may be a familiar part of your environment, but do you really know a chestnut from a fir or an ash from an elder? Well here is your chance to find out and help scientists at the Natural History Museum with one of the biggest ever urban tree surveys in the UK. Trees are essential in urban landscapes, helping to reduce noise and air pollution. But relatively little is known about them. A lot more is known about trees in the British countryside. So, scientists want to find out what types of trees you have in your gardens and neighbourhoods across the UK, and here’s how you can help. Identify the trees in your area. There are guides and keys for 80 of the most common urban trees on the website www.nhm.ac.uk/trees. Scientists then want you to record the tree types you find in the online map of Britain. ‘Trees are more than just scenery,’ says Bob Pr