The Northern Sierra Madre Natural Park, also known as the Palanan complex or Wilderness Area, is in eastern Isabela Province, in the northern half of the Sierra Madre mountain range. It is bounded by the Dikatayan River to the north, the Disabungan River to the south, the Cagayan Valley to the west and the Philippine Sea to the east. The topography within the park ranges from relatively low hills with moderately steep slopes near the coast to higher mountains with very steep slopes, peaks and sharp ridges in the interior of the Sierra Madre Mountain Range. A series of peaks along the north to south range running through the park rise to well over 1,000 m, including Mt Cresta (1,672 m), Mt Divilacan (1,311 m), Mt Palanan (1,184 m) and Mt Dipalayag. The limestone area south of Palanan Point exhibits a karst topography, with knobby hills and numerous depressions. The park is unique on Luzon in the extent of undisturbed lowland dipterocarp rainforest, and because it includes areas where undisturbed forest extends from the coast to the mountain peaks. There are some extensive areas of montane forest around the higher peaks in the park, and forest over limestone, forest AND over ultramafic rocks. The large tracts of primary forest that remain intact in this part of the Sierra Madre Mountains are a complete contrast to the adjoining Cordillera and Caraballo mountain ranges, which are heavily deforested and degraded. The rivers and streams that flow from the park’s extensive forests are one of the main sources of water for domestic, agriculture and industrial use in northeastern Luzon. Along the park’s coastline are other ecosystems, which are among the most diverse and productive in the world. These include estuaries, mangroves, beach forest, seagrass-beds, and coral reefs. They are particularly important as nesting grounds for some threatened endemic birds, turtles, and estuarine crocodiles, or as spawning and nursery area for many commercially important fishes, crabs and shrimps. The attractive scenery and beaches of this IBA have great potential for tourism. Most of the inhabitants in this IBA are immigrants (and the descendants of immigrants) from nearby provinces, and from as far as the Bicol and Visayas regions. There are at least 1,000 indigenous Agtas, who practice a nomadic lifestyle in the park. The mineral reserves in this protected area include copper, gold, manganese, chromite, zinc, nickel and possibly uranium. Some of the main deposit areas are in Palanan, San Mariano and Dinapigue.
Surveys of this IBA were conducted in 1991-1992 by a team from the DENR, BirdLife International, Danish Ornithological Society (DOF) and Zoological Museum of Copenhagen University. They confirmed that the extensive areas of pristine forest included in Northern Sierra Madre Natural Park make it the single most important site for the conservation of birds on Luzon, and possibly in the whole of the Philippines. Most of the restricted-range and threatened birds found on the Luzon Endemic Bird Area have been recorded there, and many of them clearly have large populations within the park boundaries. Several pairs of Philippine Eagle have been proveN to nest in the park and the Philippine Hawk-eagle, another large bird-of-prey, may also have a significant population there. There are large areas of lowland forest in the park, so it is of particular importance for threatened lowland forest specialists such as Green Racquet-tail, Celestial Monarch and possibly the little-known Isabela Oriole. The montane forests, e.g. on Mt Dipalayag, are less extensive, but they support several threatened species, including Whiskered Pitta and Luzon Water-redstart.
Non-bird biodiversity: Results of the baseline biodiversity surveys conducted in 1997 by the Nordic Agency for Development and Ecology (NORDECO) showed that the area supports a great number of threatened and near-threatened endemic mammals, including the Philippine Warty Pig Sus philippensis, Philippine Brown Deer Cervus mariannus, Long-Nosed Luzon Forest Mouse Apomys sacobianus, Luzon Shrew Crocidura grayi, Golden-crowned Flying Fox Acerodon jubatus), Small Rufous Horseshoe Bat Rhinolopus subrufus and Luzon Pygmy Fruit-bat Otopteropus cartilagonodus. With an estimated minimum of 70,000 flying foxes sighted, this is probably the largest roost of flying foxes in the country. Golden-crowned Flying Fox is one of the several species using the roost. The park may have populations of the two rodents endemic to northeast Luzon. Threatened or near-threatened amphibians and reptiles were also recorded in the area, including the Malayan Fresh-Water Turtle Cuora amboinensis, Philippine Sail-fin Water Lizard Hydrosaurus pustulatus, Estuarine Crocodile Crocodylus porosus and Gray’s Monitor Lizard Varanus olivaceus. At least 12 amphibians and 15 reptiles recorded from the area are Philippine endemics. Records also include several undescribed species of tree frogs Platymantis sp. and other species not previously known from the park and from the Philippines. Totals of 51 species of butterflies and 192 species of fish, molluscs and crustaceans were recorded in the area, and 29 of the butterflies were endemic to the Philippines. This IBA is also known to hold many endemic and rare species of plants. An estimated 1,500 vascular plant species occur there, of which it is believed that more than 50 are locally endemic. The area also supports threatened marine species, including the Green Turtle Chelonia mydas, Hawksbill Turtle Eretmochelys imbricata, Philippine Crocodile Crocodylus philippensis, Estuarine Crocodile Crocodylus porosus and Dugong Dugong dugon.
BirdLife International (2021) Important Bird Areas factsheet: Northern Sierra Madre Natural Park. Downloaded from http://www.birdlife.org on 18/01/2021.