Many of the sites listed below are located within this National Park. This is a dense sessile oak woodland, with classical tree species as well as some ground flora. The lichen Lobaria pulmonaria is present, as well as the snail Spermodea lamellata , the only location for this declining species in South and West Wales. Both of these species are indicators of old woodland. The vegetation is rich with relict heath, maritime grassland, crevice communities and open rock areas.
Lichens are abundant with many rare species.
Good populations of interesting invertebrates occur and grey seals breed in caves and on the small beaches. There is a wide range of littoral communities and species and the foreshore is included in the Skomer Marine Nature Reserve, as are adjacent sublittoral habitats. These two islands and associated islets are separated from the mainland by Jack Sound, a narrow channel suffering extreme tidal currants. A sub-species of bank vole, the Skomer vole Clethrionomys glareolus skomerensis is found only here. The grey seal breeds in caves and on beaches, over 100 pups are born here annually.