National nature reserves in England are designated by Natural England as key places for wildlife and natural features in England. They were established to protect the most significant areas of habitat and of geological formations. NNRs are managed on behalf of the nation, many by Natural England themselves, but also by non-governmental organisations, including the members of The Wildlife Trusts partnership, the National Trust, and the Royal Society for the Protection of Birds. There are 229 NNRs in England covering 939 square kilometres (363 square miles). Often they contain rare species or nationally important species of plants and animals.