Mindanao-Eastern Visayas rainforests
From The Encyclopedia of Earth
Ecoregions (main)
Borboanon Falls, Philippines (Photograph by Cynthia Gneiser / Zegrahm Expeditions)
May 6, 2014, 5:57 pm
Mt. Konduko, Biliran, Phillippines (Photograph by L. Heaney)
This ecoregion features lowland and hill forests on a number of large Philippine islands that, though currently disconnected, were part of one island during the height of the last ice age. These islands harbor Philippine warty pigs, Philippine deer, the Philippine tarsier, flying lemurs, and some of the last strongholds of the charismatic Philippine eagle. Most lowland forest has been cleared from the islands, but some large patches of hill and montane forest remain (the montane forest is a separate ecoregion). Tiny Camiguin Island, with two strictly endemic mammals of its own, is a unique feature of this ecoregion.
Location and General Description
WWF
This ecoregion includes the lowland (less than 1,000 meters (m) elevation) on the main islands of Mindanao, Samar, Leyte, Bohol, and numerous smaller satellite islands, including Biliran and Basilan. The climate of the ecoregion is tropical wet. The northern Visayas (northern portions of Samar and Leyte) are in the main typhoon track that so strongly influences the more northerly Philippine islands. These typhoons typically occur from July to November: As much as one-third of an island's total annual precipitation may be collected during typhoon events. Mindanao is south of the main typhoon track.
Mindanao and the Visayas were transported across the western Pacific to their present location during the last 25 million years. Most of these islands have been uplifted above water only in the last 15 million years or less. During the Pleistocene, Mindanao, Samar, Leyte, and Bohol were all one island, Greater Mindanao, and their faunal affinities to each other persist to this day.
Vegetation types on Mindanao and in the Eastern Visayas originally included beach forest, mangroves, lowland rainforest, and more open forest at higher elevations up to 1,000 m.
The stunted beach forest contains Casuarina and Barringtonia mixed with other lowland species. Palms, vines, bamboo, and Pterocarpus indicus are present only in rare back-beach swamps. This habitat type is extremely rare because of coastal habitation.
The dominant forest type in the Mindanao lowlands and the rest of the Philippines was dipterocarp forest. This group of trees is known as Philippine mahogany in the timber trade. This forest type occurred from sea level to elevations of 400 m or higher. Individual dipterocarps occur to 1,500 m. Philippine dipterocarp forest is quite tall (45-65 m) and dense, with three canopy layers. Lianas and bamboo are rare in mature forest but common in poorly developed evergreen forest. Ferns, orchids, and other epiphytic plants are found on the larger trees. At higher elevations there are only two canopy layers, tree stature is lower, and there are more epiphytes. Upper hill dipterocarp forest is found at elevations of 650 to about 1,500 m and contains dominant Shorea polysperma and oaks, chestnuts, and elaeocarps.
Biodiversity Features
Borboanon Falls, Philippines (Photograph by Cynthia Gneiser / Zegrahm Expeditions) Mindanao and its neighbor, Basilan, situated adjacent to the Sulu Archipelago, have been influenced by immigration from Borneo although in recent millennia movement has been primarily in the other direction. During the most recent ice ages, the Mindanao faunal region has developed its own unique fauna, with a large number of endemic vertebrates.
Tiny Camiguin Island (ca. 265 square kilometers (km2)) contains two strictly endemic and as yet undescribed mammal species: a small forest mouse (Apomys sp.) and a large moss-mouse (Bullimus sp.), in addition to an endemic frog. Several taxa found on Mindanao, only a short distance away, are absent from Camiguin, including squirrels, some murid rodents, flying lemurs, tarsiers, and deer. Camiguin is the smallest island in the Philippines known to have unique mammal species. Consisting of a series of active volcanic cones reaching a maximum elevation of 1,713 m, the island is surrounded by deep water. Fortunately, the island still has good forest cover.
|
Table 1. Endemic and Near-Endemic Mammal Species. Family Species Erinaceidae Podogymnura aureospinula* Soricidae Crocidura beatus Tupaiidae Urogale everetti Cynocephalidae Cynocephalus volans Pteropodidae Ptenochirus minor Rhinolophidae Hipposideros coronatus* Sciuridae Sundasciurus philippinensis Muridae Bullimus bagobus Muridae Batomys salomonseni Muridae Batomys russatus* (Dinagat only) Muridae Crateromys australis*(Dinagat only) Muridae Crunomys melanius* Muridae Apomys sp. D*(Camiguin only) Muridae Bullimus sp. A*(Camiguin only) Muridae Tarsomys echinatus* Sciuridae Exilisciurus concinnus An asterisk signifies that the species' range is limited to this ecoregion. There is also variation (Mindanao-Eastern Visayas rainforests) within the island of Mindanao. Thirty-one bird species are polytypic on the island. Sixteen of these variations are based on differences between isolated mountain ranges, and seven species have races associated with the Zamboanga Peninsula and Basilan Island. There are three species that vary between the uplands and lowlands. Approximately 80 percent of Greater Mindanao's nonvolant mammal species are found nowhere else in the world. Whereas flying lemurs, tree shrews, tree squirrels, and tarsiers are found on the islands of Greater Mindanao, they are not found on the other large Philippine island, Luzon, just 25 kilometers (km) from the northern tip of Samar. More than 30 percent of nonvolant mammals in the ecoregion are endemic to Mindanao only, but the other islands in the ecoregion generally share their species with Mindanao. However, tiny Dinagat island, located just north of Mindanao, contains three of its own endemic mammals, including the endangered Dinagat Island cloud-rat (Crateromys australis). There are sixteen endemic or near-endemic mammal species in the ecoregion (Table 1). An endemic subspecies of Philippine deer (Cervus mariannus nigricans) is limited to Mindanao. Philippine deer are widespread (though patchily distributed) in the Philippines, being found on Luzon, Mindoro, Samar, Leyte, Mindanao, and the Basilan Islands. The subspecies is threatened by habitat loss and hunting. It has been reported that the endangered Visayan or Philippine spotted deer (Cervus alfredi) was potentially found on Bohol Island, but it seems likely that these reports refer to Cervus mariannus. Cervus alfredi is not found on Bohol. The kagwang (Cyanocephalus volans), or Philippine flying lemur, is also endemic to Greater Mindanao; the only other species of this unique order of mammals is found in Malaysia and Indonesia. These small nocturnal mammals glide between trees for distances up to 135 m. Fortunately, the kagwang actually prefers second-growth forests to old growth, so they are more secure than other Philippine mammals. However, the species is still considered vulnerable. The ecoregion also supports a population of the Philippine warty pig (Sus philippensis), which the The Conservation Union (IUCN) considers rare and declining. The Philippine warty pig is widely but patchily distributed in the still-forested areas of Luzon, Mindoro, Samar, Leyte, Mindanao, and some of the smaller satellite islands. Many of these forested areas are found in existing national parks. The Philippine warty pig is closely related to Sus barbatus of the Greater Sundas and was once thought to be a subspecies, analogous to the Palawan bearded pig (Sus barbatus ahoenobarbus). This species is still threatened by hunting and habitat loss. Greater Mindanao is also home to an endemic primate, the Philippine tarsier (Tarsius sychrita), which is found on Samar, Leyte, Dinagat, Siargao, Bohol, Mindanao, and Basilan. Although they are also found in primary forests and mangroves, these highly charismatic small mammals seem to prefer second-growth forests, and they are not considered threatened by the IUCN. {| border="1" cellpadding="3" align="right" ! colspan="3" | Table 2. Endemic and Near-Endemic Bird Species. Family Common Name Species Rallidae Brown-banded rail Lewinia mirificus Columbidae Mindanao bleeding-heart Gallicolumba criniger* Columbidae Mindanao brown-dove Phapitreron brunneiceps Columbidae Grey imperial-pigeon Ducula pickeringii Cuculidae Black-faced coucal Centropus melanops* Strigidae Mindanao eagle-owl Mimizuku gurneyi Apodidae Philippine needletail Mearnsia picina Alcedinidae Silvery kingfisher Alcedo argentata* Alcedinidae Blue-capped kingfisher Actenoides hombroni Bucconidae Mindanao hornbill Penelopides affinis Bucconidae Samar hornbill Penelopides samarensis* Bucconidae Writhed hornbill Aceros leucocephalus Pittidae Azure-breasted pitta Pitta steerii* Eurylaimidae Wattled broadbill Eurylaimus steerii* Eurylaimidae Visayan wattled broadbill Eurylaimus samarensis* Rhipiduridae Blue fantail Rhipidura superciliaris* Monarchidae Short-crested monarch Hypothymis helenae Monarchidae Celestial monarch Hypothymis coelestis Muscicapidae Little slaty flycatcher Ficedula basilanica* Muscicapidae Cryptic flycatcher Ficedula crypta Pycnonotidae Zamboanga bulbul Ixos rufigularis* Pycnonotidae Yellowish bulbul Ixos everetti Sylviidae Long-tailed bush-warbler Bradypterus caudatus Sylviidae Rufous-headed tailorbird Orthotomus heterolaemus Sylviidae Yellow-breasted tailorbird Orthotomus samarensis* Sylviidae White-browed tailorbird Orthotomus nigriceps* Sylviidae White-eared tailorbird Orthotomus cinereiceps* Timaliidae Striated wren-babbler Ptilocichla mindanensis* Timaliidae Pygmy babbler Stachyris plateni Timaliidae Rusty-crowned babbler Stachyris capitalis Timaliidae Brown tit-babbler Macronous striaticeps Timaliidae Miniature tit-babbler Micromacronus leytensis Paridae White-fronted tit Parus semilarvatus Dicaeidae Whiskered flowerpecker Dicaeum proprium Dicaeidae Olive-capped flowerpecker Dicaeum nigrilore Dicaeidae Flame-crowned flowerpecker Dicaeum anthonyi An asterisk signifies that the species' range is limited to this ecoregion. The Philippine tree shrew (Urogale everetti), in the order Scandentia, which is found on Mindanao, Dinagat, and Siargao Islands, represents an endemic, monotypic genus. Worldwide there are sixteen species of tree shrew, a diurnal animal that resembles a squirrel but whose dentition, circulatory system, and large braincase are more like those of primates. This species is considered vulnerable. Greater Mindanao also supports an endemic genus of Erinaceidae, Podogymura. There are two moonrat species in this genus, both of which are found in Greater Mindanao. One species is found in the adjacent montane ecoregion of Mindanao (Mindanao-Eastern Visayas rainforests) (P. truei), and the other (P. aureospinula) is found in the lowland forest of Dinagat, Siargao, and the Bucas Grande Islands. Lowland Greater Mindanao is home to endangered mammals also found in other parts of the Philippines, including the golden-capped fruit bat (Acerodon jubatus) and the mottle-winged flying-fox (Pteropus leucopterus) (found on Luzon and Dinagat). This ecoregion overlaps with the Mindanao and Eastern Visayas Endemic Bird Area (EBA), with the exception of the montane areas above 1,000 m, which have been given their own ecoregion. The EBA contains fifty-one restricted-range birds, twenty-four (or possibly twenty-five) of which are lowland and hill forest specialists and are thus resident in this ecoregion. All the restricted-range birds are forest species. The ecoregion contains thirty-six endemic or near-endemic bird species. Nine of these species are threatened, including the endangered Mindanao bleeding-heart (Gallicolumba criniger). The remainder of the threatened species are considered vulnerable. This situation should be contrasted with the adjacent upland Mindanao montane rainforests ecoregion. Although the upland ecoregion contains more restricted-range species, only one of these is considered threatened. In addition to the restricted-range species, several widespread threatened species are found in the ecoregion, including the critically endangered Philippine eagle (Pithecophaga jeffreyi) and Philippine cockatoo (Cacatua haematuropygia). Four additional widespread but vulnerable species are also found in the ecoregion. The critically endangered Philippine crocodile (Crocodylus mindorensis) was historically found on Jolo, Luzon, Mindoro, Masbate, Samar, Negros, Busuanga, and Mindanao, but the only remaining [[population]s] are found on Mindoro, Negros, Mindanao, and Busuanga. The current wild population may be approximately 100 nonhatchlings. Mt. Apo, on Mindanao, is considered a Centre of Plant Diversity. This spectacular mountain in the southern portion of the Central Cordillera contains primary lowland forest and lower montane forests as well as montane forests found in the Mindanao montane rainforests ecoregion. Much of the lowland forest below 1,000 m has been cleared, but dipterocarp forest is found from 1,000 to 1,600 m. ==Current Status== All the islands in the ecoregion were once completely forested, but there is little forest left on most islands, and especially little lowland forest left. The dire situation in the lowlands of Mindanao and Eastern Visayas is highlighted by the contrast in conservation status between the lowland ecoregion and the adjacent upland [[Mindanao Montane Rainforests] ecoregion]. Although the upland ecoregion contains more restricted-range species, only one of these is considered threatened. In fact, the Mindanao and Eastern Visayas EBA contains more threatened birds than any other EBA in the southeast Asian island region, and all but one of these are found in the lowlands. Bohol is heavily deforested, and almost all of the island's natural forest is to be found in Rajah Sikatuna National Park (RSNP). The conditions in this 9,023-hectare (ha) area are good, however, and the Philippine Department of Natural Resources is actively reforesting the edges of the park. Both of the Eastern Visayan endemic birds and all four of Bohol's endemic bird subspecies can be found in RSNP. Problems of firewood and rattan collection, hunting and trapping, and slash-and-burn agriculture are effectively limited to the eastern portions of the park. {| width="30%" border="1" cellpadding="3" align="right" ! colspan="3" | Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion. Protected Area Area (km2) IUCN Category Mado Hot Spring 20 III Sohoton Natural Bridge 40 III Imelda Lake 40 II Mahagnao Volcano 30 II Lake Danao 5 IV Rajah Sikatuna 110 II Rizal 10 III Initao 10 V Mt. Malindang 160 II Mt. Apo 130 II Lake Butig 6 V Liguasan March GRBS 410 IV Lake Buluan 80 IV Agusan Marsh 810 PRO Basilan 90 II Total 1,951 Samar and Leyte each have two areas of closed-canopy forest remaining. The largest blocks are found on Samar. Three of these patches are found in areas of suspended timber license agreements and the remaining forest block, on Leyte, is found in the Philippine National Oil Company Tungonan Forest Reserve. By 1988, approximately 29 percent of Mindanao's forest remained, including both primary and secondary forests. There is much less today. The Zamboanga Peninsula on southwest Mindanao contains a number of isolated fragments (Mindanao-Eastern Visayas rainforests) , the largest of which is found in the watershed of Zamboanga City. The remaining patches are scattered in hill and montane areas around the peninsula. These patches contained evidence of recent logging in 1992. In southern Mindanao, some large areas of forest remain in hill and montane areas. Political instability, lack of access, and poor commercial values have helped protect some of these areas. Ironically, some of the areas, which had been under now-suspended timber license agreements, are threatened by encroaching agriculture and fire. There are other large blocks of forest in the rest of Mindanao, but they are similarly limited to hill and montane areas; there is very little lowland dipterocarp forest remaining on Mindanao. Southern Mindanao is faced with political instability that poses a challenge for active conservation. Aerial surveys of Basilan in 1992 revealed less than 2 percent natural forest remaining. Unfortunately, Basilan is also subject to political insurgency that makes active conservation efforts quite difficult. Both the Philippine warty pig and Philippine deer suffer from intense hunting pressure and fragmentation of their remaining [[habitat]s]. The pigs are in an especially poor situation because they tend to raid crops and are regarded as pests; consequently, no protections are in place for them. Table 3 details the existing protected areas on the island. ==Types and Severity of Threats== Many of the factors that have contributed to the loss of habitat in the past still present threats to the future of these forests. They include firewood and rattan collection, hunting and trapping, slash-and-burn agriculture, and commercial forestry. ==Justification of Ecoregion Delineation== MacKinnon identified seven subunits in the Philippines and the Philippine Biodiversity Action Plan (BAP) demarcated fifteen biogeographic units. Udvardy identified the Philippines as a single biogeographic province. We delineated nine ecoregions in the Philippine islands, including Palawan. We deviated from Udvardy, MacKinnon, Stattersfield, and the Philippine BAP in varying degrees and based our delineation of the Philippine ecoregions on Heaney, with the exception of Camiguin, which Heaney separated. The islands of Leyte, Samar, Dinagat, and Bohol were combined with the lowland rainforests of Mindanao island to form the Mindanao-Eastern Visayas Rain Forests. We also included the Basilan Islands off the southwest peninsula of Mindanao in this ecoregion, based on Heaney (1993). In Mindanao we used the 1,000-m contour from the Department of Environmental Management (DEM) to delineate the montane forests from the lowland forests. The montane forests of Mindanao were placed into their own ecoregion, the Mindanao montane rainforests. In our delineation of the Mindanao-Eastern Visayas Rain Forests and Mindanao Montane Rain Forests ecoregions, we deviated from MacKinnon. MacKinnon placed both of Mindanao's lowland and montane forests in a single subunit (26c). The Basilan Islands were part of subunit 26d, and the islands of Leyte and Samar made up subunit 26e. ==Additional Information on this Ecoregion== * For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion. * To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion. * World Wildlife Fund Homepage |
|---|
