Northern Sporades is a group of islands in the Northwest Aegean situated north of Evia and east of Pilio. The area comprises islands Alonnisos, Skopelos and Skiathos, which are its only inhabited territories, as well as a number of smaller islands and islets on which human presence is limited to a few guards and occasional shepherds. The largest part of the area (94%) is covered by water. Geologically, the majority of islands consist mostly of limestone rock, with the exception of Psathoura featuring a geology of purely volcanic origin. In proximity to Psathoura lies a dormant volcano. On the island of Skopelos valleys with steep slopes and streams are formed. The local vegetation is chiefly made up of forests of Aleppo pines (Pinus halepensis), holly oak maquis (Quercus coccifera), a small forest of holm oaks (Quercus ilex), Oleo-Ceratonion maquis, fruit trees and olive groves. The plant life of Alonnisos mainly consists of dense maquis with Quercus coccifera, Q. ilex, Arbutus unedo, Juniperus phoenicea, forests of Aleppo pines (Pinus halepensis) and brushwood (Sarcopoterium spinosum). The pine forests on Skopelos and Alonnisos have replaced oak species that predominated in the past; this is due to a preference for pine trees, since their timber is widely used for ship construction. The National Marine Park is a unique group of Mediterranean biotopes, both on land and in the sea. It encompasses many types of vegetation and highly representable marine natural habitats. The park is also home to many plant and animal species, including endemic, rare or protected species, as well as taxa at the southernmost or northernmost end of their spread. Piperi island is an area protected under the Barcelona Convention.
Apart from its scientific and educational interest, the area also is of great archaeological interest, considering the number of remnants and monuments dating from the prehistoric, classical and Byzantine eras (speleological findings, shipwrecks, old monasteries and churches). The numerous caves and beaches formed between the rocky coasts constitute an ideal habitat for the monk seal, whose population in the area is estimated to be the largest in the Mediterranean. Piperi, the most important breeding site for the monk seal, is the core of the Northern Sporades Marine Park. An isolated population of wild goats (Capra aegagrus ssp. Dorcas) occurs exclusively on the island of Gioura. Equally important is the local reptilian fauna comprising rare and protected species. Birdlife in the area is abundant, with a large number of migratory birds and many species breeding in the area. The invertebrate fauna is also significant, as it consists of endemic species of isopods, especially in the Cave of Cyclops on Gioura. Marine biotopes are renowned for sustaining a great many well-populated species. This wide marine biodiversity is partly attributed to the diversity of marine natural habitats (such as underwater sea-grass beds of Posidonia, reefs, etc) and absence of pollution. This fact renders the recommended site especially important from a systematical and zoogeographical point of view. Furthermore, 170 species of fish, 70 species of amphipods and 40 species of sponges have been recorded in the area. The lush chasmophyte vegetation comprising many endemic species presents great phytogeographical and ecological interest.Some species are spread over the Southern Aegean, and Gioura constitutes the northernmost end of their spread.