It is a center of plant and animal diversity and endemism in the Philippines containing a number of threatened species belonging to the Eastern Visayas and Mindanao biogeographic region.

It extends from the Northern Samar municipalities of Catubig, Las Navas, Lope de Vega, Mondragon and Silvino Lobos in the north to the Eastern Samar municipalities of Arteche, Balangiga, Balangkayan, Borongan, Can-avid, Dolores, General MacArthur, Giporlos, Hernani, Jipapad, Lawaan, Llorente, Maslog, Maydolong, Oras, Quinapondan, San Julian, Sulat and Taft; and the Samar Province municipalities of Basey, Calbayog, Calbiga, Catbalogan, Gandara, Hinabangan, Jiabong, Marabut, Matuguinao, Motiong, Paranas, Pinabacdao, San Jorge and San Jose de Buan in the island's central and southern regions.

The endemic giant forest raptor was first spotted in the island in the municipality of Paranas on June 15, 1856, by the British explorer John Whitehead.

[13] The Jicontol Watershed Forest Reserve, first gazetted in 1992 and reclassified as a natural park in 1998,[14][15] covers 6,483 hectares (16,020 acres) in the municipalities of Dolores, Can-avid and Maslog.

This forest is home to many threatened and restricted-range species of the Mindanao and Eastern Visayas Endemic Bird Area, such as the Samar hornbill, Visayan broadbill and yellow-breasted tailorbird.

[16] Its forest cover consists of typical dipterocarp and molave-dipterocarp with mid mountain type vegetation in the highest peaks reaching to 850 metres (2,790 ft).

[17] The 4,055-hectare (10,020-acre) forest park borders the Sulat River to the north and west, and includes Mount Honop, its highest peak at 731 metres (2,398 ft).