Palawan rainforests
Coron Island, Philippines. (Photograph by Sterling Zumbrunn/Conservation International)
Introduction Palawan represents a bridge between the Sunda Shelf and Philippine bioregions and contains faunal elements from both, as well as it own unique elements. This ecoregion (Palawan rainforests) , though more intact than any other region in the Philippines is under great pressure from logging interests.
Location and General Description 
WWF
This ecoregion includes the island Palawan plus Balabac, Ursula Island, and the Calamian Group. Palawan itself is the sixth largest of the Philippine Islands. The climate of the ecoregion is tropical wet. In northwest Palawan, a dry season lasts from November to May while the wet season lasts from June to October; the rest of the island experiences a short, one- to three-month dry season. The east coast becomes progressively drier than the west coast from north to south.
Palawan (along with the Calamianes and the island of Mindoro) was rifted (below water) from the Asian mainland approximately 32 million years ago, transported through seafloor spreading across the growing South China Sea, added to the growing Philippine Archipelago approximately 17 million years ago, and uplifted above water approximately 5-10 million years ago. Metamorphic rocks are found in the northern portion of the island north of Mt. St. Paul. Volcanic rocks are found in the vicinity of Cleopatra's Needle, just south of Mt. St. Paul. Mt. St. Paul itself and the El Nido Cliffs are karst landscapes. The southern third of the island, south of the Quezon-Aboabo Gap, is dominated by ultramafics mixed with volcanic rocks and Tertiary limestone. Tertiary sandstones and shales occur along the southwest coast.
The channel between Palawan and Borneo is about 145 meters (m) deep. During the middle Pleistocene, sea levels were 160 m lower than today, and the islands were connected. During the last ice age (late Pleistocene), sea level was approximately 120 m below current levels, and Palawan was separated from ice age Borneo by a narrow channel. Palawan has always remained separated from the rest of the Philippines. Palawan is long and narrow, consisting of a steep mountain range whose highest point is 2,085 m (Mt. Mantalingajan). More than 45 percent of Palawan consists of mountains with slopes greater than 30 percent.
Vegetation types on Palawan are diverse and include beach forest, tropical lowland evergreen dipterocarp rainforest, lowland semi-deciduous forest, montane forest, and ultramafic and imestone forest. Beach forest merges with other forest types away from the coast and includes Calophyllum inophyllum, Canarium asperum var. asperum, Pometia pinnata, Palaquium dubardii, and Ficus spp..
The lowland evergreen dipterocarp rainforest, which naturally occupies 31 percent of the island, is dominated by Agalai spp., Dipterocarpus gracilis, D. grandiflorus, Ficus spp., Tristania spp., Exocarpus latifolius, and Swintonia foxworthyi. Sygium spp., Dracontomelon dao, and Pongamia pinnata are emergent. Lianas and cycads are common. In southern Palawan, a Casuarina sp. dominates in the lowland forests.
The eastern half of the island is in a rain shadow and contains moist semi-deciduous forests. Soils are thin on the steeper slopes and support medium-sized trees (up to 15 metres tall), which shed their leaves during the March-May dry season. The rainy season is June-July. Common tree species (Biodiversity) include Pterocymbium tinctorium, Pterospermum diversifolium, Hymenodictyon spp., and Garuga floribunda.
Montane forests, found between 800 and 1,500 m, are dominated by Tristania spp., Casuarina spp., Swietenia foxworthyi, and Litsea spp. in the lower elevations. Upper montane forest trees include Agathis philippinensis, Dacrydium pectinatum, Podocarpus polystachyus, Gnetum latifolium, Cycas wadei, Cinnamomum rupestre, Nepenthes philippinensis, and Angiopteris spp.
Limestone forests are found on the islets surrounding Palawan and over large areas in the southern portions of the island. Represented are Euphorbia trigona, Aglaia argentea, and Antidesma, Drypetes, Gomphandra, Sterculia, Pleomele, and Begonia spp.
Victoria Peak, in south-central Palawan, contains the largest region of ultramafic forest on the island. Although many of the ultramafic tree species are shared with semi-deciduous forest, several species, including Scaevola micrantha, Brackenridgea palustris var. foxworthi, Exocarpus latifolius, and Phyllanthus lamprophyllus are believed to be heavy metal indicators.
Biodiversity Features
Relative to the size of Palawan, the ecoregion contains a rich fauna, including several groups that are not found in the rest of the Philippines (carnivores, pangolins, porcupines, and some insectivores).
There are many endemic mammals in Palawan, but nearly all the genera (96 percent) are also found in Borneo. Of twenty-five indigenous nonvolant mammal species, eleven (44 percent) are endemic to Palawan, and the remainder are shared with Borneo. Therefore, the greater Palawan region is rightly considered part of the Sunda Shelf bioregion rather than that of the Philippines. The large number of endemic species (Biodiversity) but few endemic genera of Palawan are consistent with a separation of Borneo and Palawan of approximately 160,000 (since the middle Pleistocene). There are fifteen endemic or near-endemic mammals in greater Palawan (Table 1).
Table 1. Endemic and Near-Endemic Mammal Species. Family Species Pteropodidae Acerodon leucotis* Cervidae Axis calamianensis* Sciuridae Sundasciurus steerii* Sciuridae Sundasciurus moellendorfi* Sciuridae Sundasciurus rabori* Sciuridae Hylopetes nigripes* Muridae Chiropodomys calamianensis* Muridae Maxomys panglima* Muridae Palawanomys furvus* Hystricidae Hystrix pumila* Sorcidae Crocidura palawanensis* Muridae Haeromys sp. A* Sciuridae Sundasciurus hoogstraali* Sciuridae Sundasciurus juvencus* Tupaiidae Tupaia palawanensis* An asterisk signifies that the species' range is limited to this ecoregion. The Calamian deer (Axis calamianensis) is found only in the Calamian Islands, where it survives in low densities on Busuanga, Calauit, and Culion Islands. The only protected area for this species was established to protect free-ranging African ungulates on Calauit Island. Balabac, Palawan, and the Calamian Islands also provide habitat (Palawan rainforests) for an endemic subspecies of the bearded pig (Sus barbatous ahoenobarbus), another subspecies of which is widely distributed in the Greater Sundas. The World Conservation Union (IUCN) considers this species to be rare and declining. This species naturally inhabits tropical evergreen rain forest but is able to use a wide variety of habitats within forests. They are quite dependent on fruit supplies but consume a wide variety of foods. Directional large-scale population movements in scattered or condensed herds lasting days, weeks, or even months are reported for other subspecies in Borneo and Sumatra; this is generally associated with the mast fruiting of dipterocarps. Such movements have not been reported from the Philippines.  Palawan Island, Philippines. (Photograph by Conservation International) Several of Palawan's endemic mammals are considered threatened. Three endemic mammal species are considered endangered, including the Calamian deer, a Sunda tree squirrel (Sundasciurus juvencus) (recommended for delisting), and the Palawan rat (Palawanomys furvus), which was collected only four times in 1962. A subspecies of mouse deer, the Balabac chevrotain (Tragulus napu nigricans), which is confined to Balabac Island, is also considered endangered. Five endemic mammal species are considered vulnerable, including Acerodon leucotis, the Palawan treeshrew (Tupaia palawanensis), the Palawan stink badger (Mydaus marchei), the Palawan binturong (Arctictis binturong whitei), and a Sunda tree squirrel (Sundasciurus rabori). As with mammals, Philippine birds in general show a strong Bornean affinity, and it is clear that the main pathway of Asian immigration to the Philippines was through Palawan; of 395 Philippine breeding species, 137 (35 percent) also breed in Borneo. Palawan birds exhibit strong differentiation at the subspecific level when compared with its nearest Philippine neighbor, Mindoro. This is in contrast to the other partial land bridge between Borneo and the Philippines, the Sulu Islands, which have not differentiated significantly from Mindanao. Borneo and Palawan share twenty-three bird species that are not found in the rest of the Philippines. The Asian genera Polyplectron, Malacocincla, Malacopteron, Dinopium, Aegithina, Criniger, Seicercus, and Gracula are found only in Palawan within the Philippines. The island forms an important bird migration route between Borneo and the rest of the Philippines for southern migrants. This ecoregion corresponds exactly with the Palawan EBA. The EBA contains twenty restricted-range birds, seventeen of which are found nowhere else on Earth and five of which (Palawan peacock-pheasant Emphanum, grey imperial-pigeon Pickeringii, blue-headed racquet-tail Platenae, falcated wren-babbler Falcata, and Palawan flycatcher Platenae) are considered vulnerable. All these vulnerable birds are dependent on lowland and hill forest. There are twenty endemic or near-endemic bird species in the Palawan ecoregion (Table 2).
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