Bird boxes are appearing around Norwich as part of a Norwich and Norfolk Festival art project.

The boxes are being wrapped around specially selected trees in three places in Norwich this week as part of the specially commissioned festival project.

Artists Jo Joelson and Bruce Gilchrist, based in London and known as London Fieldworks, have created the work called Spontaneous City to reflect local architecture and interact with nature.

Over 400 durable wooden boxes of various shapes and sizes were arranged around the trunks of a large tree by Norwich tree surgeons Tully King and Aaron Tattersall from Eastern Tree Care.

They are based at RAF Coltishall and have worked with the artists from the beginning of the project.

Ms Joelson explained how the structures work.

She said: 'It is an art project, but they are also viable bird and bug houses. First we identified which trees we want to use, carried out surveys on them and designed these suitable structures.

'As the tree grows the whole thing will change. It has an internal substructure that is designed to expand as the tree grows. It will be affected by the weather. Things will grow in it and bloom.'

The artists are keen to emphasise the natural side of the work. They aim to encourage people to interact with the tree and spend time looking it and using it as inspiration.

Mr Gilchrist added that there many layers to the work they had created. He said: 'There has been a huge decline in bird populations. These are effectively empty houses. Where have they all gone? Spontaneous City is a symbol of crisis in nature.'

He said the boxes also represent the living situations of high density populations in places such as India and Brazil. Ms Joelson and Mr Gilchrist will be giving talks in the community as part of the project. Bird box sculptures are already up in Eaton Park and Waterloo Park and will now be installed near Cow Tower, next to the River Wensum.

• NNF11 runs from May 6 to 21. For more information go to www.nnfestival.cor.uk/nnf11