The Northern Sierra Madre Natural Park (NSMNP) is the largest and most diverse protected area in the country, covering a total of 359,486 hectares of terrestrial and coastal areas in Isabela Province. It is one of ten priority sites of the National Integrated Protected Area System (NIPAS). NSMNP is home to numerous species of flora and fauna, many of which are rare and endangered. These include a large number of commercially important but severely threatened tree species of the dipterocarp family such as Shorea spp. and Hopea spp.
CI and its partners provided the scientific justification for establishing the NSMNP as a protected area. Biological surveys in the 1990s showed that the area contained 240 bird species – 78 of these are found nowhere else in the country. Biologists found several species of tree frogs previously undescribed by science. The park may contain more than half of all the plant as well as bird species found in the Philippines. Two of the birds found in the park include the Philippine eagle (Pithecophaga jefferyi) and the endemic Isabela oriole (Oriolus isabellae), one of the rarest birds in the world.
NSMNP is also home to two indigenous peoples, the Agta and the Kalinga, who are highly dependent on the park's resources for their livelihood. About 25,000 migrant farmers and fishermen also live within the multiple use zone of the park and 2 million people living in Cagayan Valley depend on the ecosystem services provided by the park, notably the regulation of water flows during the dry and wet season.
CI has been working in the protected area since 1992, and is currently managing the 16-hectare Forest Dynamics Plot located in Palanan, Isabela. CI is also serving as a member of the Protected Area Management Board.