Article: The London Natural History Society suggest that London is "one of the World's Greenest Cities" with more than 40 percent green space or open water. They indicate that 2000 species of flowering plant have been found growing there and that the tidal Thames supports 120 species of fish. They also state that over 60 species of bird nest in central London and that their members have recorded 47 species of butterfly, 1173 moths and more than 270 kinds of spider around London. London's wetland areas support nationally important populations of many water birds. London has 38 Sites of Special Scientific Interest (SSSIs), two National Nature Reserves and 76 Local Nature Reserves.

Now answer this question: How many National Nature Reserves exist in the London area?
two