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Southeastern Asia: Luzon Island in the Philippines

The Luzon Rain Forests [IM0123] ecoregion is rich in endemic species and also contains one of the largest populations of the Philippine eagle Pithecophaga jefferyi. A high proportion of the ecoregion was originally forested, but now very little of this forest remains. However, the ecoregion has managed to retain one of the largest remaining tracts of primary forest in the Philippines.

  • Scientific Code
    (IM0123)
  • Ecoregion Category
    Indo-Malayan
  • Size
    36,900 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
Luzon is located in the western Pacific Ocean. It is the largest island in the Philippines and lies at the northern end of the island group. The lowland rain forests ecoregion comprises all the areas below 1,000 m on Luzon and a few isolated volcanic mountains in the south of the island that exceed 1,000 m: Mt. Maquiling, Mt. Banashaw, Mt. Isarog, Mayon Volcano, and Bulusan Volcano. The broad Cagayan River valley to north is sheltered from typhoons lying between the two north-south mountain ranges: the Cordillera Central in the west and the Sierra Madre to the east. The fertile soil of the Cagayan Valley is the biggest rice-growing region in the country. Southern Luzon is also agricultural but is subject to typhoons and comprises less area as Luzon narrows southward. Several neighboring island groups are also part of the ecoregion, including the Batanes and Babuyan Islands to the north (rather isolated but placed here for convenience), Polillo and Catanduanes to the east, and Marinduque to southwest.

The geologic history of the Philippines is very complex and has had tremendous influence on the biota currently found there. Luzon has developed many unique plant and animal species as a result of its long-standing isolation from other landmasses. Parts of the Luzon highlands were established as a result of volcanic activity and the friction of the Australian and Asian plates at least 15 million years ago. The highlands began to take their current form over the next 10 million years. Luzon therefore is oceanic in character, having never been connected to mainland Asia. Even during the Pleistocene, as world sea levels fell 120 m, Luzon expanded to become a larger island including the modern islands of Polillo, Marinduque, and Catanduanes but never connecting to other regions of the Philippines or to mainland Asia (Heaney and Regalado 1998).

Temperatures in Luzon vary greatly with elevation, but within the lowlands temperatures are fairly uniform at about 25-28°C. Rainfall in the lowlands is seasonally variable, with four distinct types. Southwestern Luzon and Marinduque Island receive rain uniformly throughout the year. The Cagayan valley and the eastern portion of the Bataan Peninsula do not have pronounced seasons but are dry from November to April. The southeastern portions of Luzon and Polillo and Catanduanes Islands have no dry season but do have a period of increased rainfall from May to January. Northwestern Luzon has two distinct seasons, being wet from May to October and dry November to April.

Lowland vegetation of Luzon is dominated by dipterocarp trees with wide buttresses at the base. These massive trees are 1-2 m in diameter and up to 60 m high. The canopy height of mature lowland forests tends to be uneven. In areas of disturbance, rattans and lianas receive the light they need to flourish in the understory. There tends to be an abundant herbaceous undergrowth, and ferns and orchids are prevalent on large branches of tall trees. Other natural habitats in the ecoregion include mangrove forests and beach forests (consisting of Casuarinas and Barrintonia) near the coasts. There also were natural grasslands in valley bottoms and on plateaus, as evidenced by the presence of several endemic buttonquail taxa needing grasslands (Collar et al. 1999).

Biodiversity Features
In terms of mammalian endemism, perhaps the most significant area of endemism in the ecoregion is Mt. Isarog, but this has only recently become apparent. Mt. Isarog is an extinct volcano and the second highest peak in southern Luzon at 1,966 m (Mt. Mayon is higher at 2,462 m). The unique character and geographic isolation of Isarog make it difficult to lump with the other two montane ecoregions of Luzon [IM0122], [IM0302], so it is considered here as part of the Luzon rain forests. The Luzon rain forest ecoregion as a whole has ten species of near-endemic mammals and five strictly endemic species (table 1). Three of the five strict endemics are found only on Mt. Isarog, and none was been described before 1981: Isarog shrew-mouse (Archboldomys luzonensis), Isarog striped shrew-rat (Chrotomys gonzalesi), and Isarog shrew-rat (Rhynchomys isarogensis). All three consume earthworms, and the latter two are strongly vermivorous. The southern Luzon giant cloud rat (Phloemys cumingi) is another of the ecoregion's strict endemics found on Isarog, but it is also found at other locations. The fifth strict endemic is the northern Luzon shrew-mouse (Crunomys fallax), known from a single specimen collected at about 300 m in the northern Sierra Madres.

Table 1. Endemic and Near-Endemic Mammal Species.

  Family Species
Pteropodidae Otopteropus cartilagonodus
Muridae Abditomys latidens
Muridae Apomys abrae
Muridae Apomys datae
Muridae Apomys microdon
Muridae Apomys sacobianus
Muridae Archboldomys luzonensis*
Muridae Batomys granti
Muridae Bullimus luzonicus
Muridae Chrotomys gonzalesi*
Muridae Crunomys fallax*
Muridae Phloemys cumingi*
Muridae Phloemys pallidus
Muridae Rhynchomys isarogensis*
Muridae Tryphomys adustus

An asterisk signifies that the species' range is limited to this ecoregion.

The ecoregion has thirteen mammal species that are listed by IUCN as threatened (categories VU and above) (IUCN 2000). One of these species is the golden-crowned flying-fox (Acerodon jubatus). It is probably the largest bat in the world (at more than 1.2 kg, perhaps reaching 1.5 kg) and is widespread in the Philippines but has undergone a precipitous decline because of heavy hunting and habitat destruction (Heaney and Regalado 1998).

Five large mammals inhabit the ecoregion: long-tailed macaque (Macaca fascicularis), Philippine warty pig (Sus philippensis), Philippine brown deer (Cervus mariannus), Malay civet (Viverra tangalunga), and common palm civet (Paradoxurus hermaphroditus). All are fairly widespread, and none are listed as threatened by IUCN (IUCN 2000). However, habitat destruction affects all these species, and hunting affects all but the civets. Additionally, the Philippine brown deer is said to be declining and is listed as data deficient by IUCN, although the species is not uncommon in appropriate habitat (Heaney et al. 1998; Wemmer 1998).

The lowland forests of Luzon contain thirty-four near-endemic bird species and six strict endemics (table 2). Only two of the strict endemics are threatened (IUCN categories VU and above): green racquet-tail Prioniturus luconensis and Isabela oriole Oriolus isabellae (Collar et al. 1999). Researchers in Luzon feared that Isabela oriole was extinct (Mallari and Jensen 1993; Poulsen 1995) until two recent reports of its existence in northern Luzon (Gamauf and Tebbich 1995; van der Linde 1995). Although these observations are encouraging, some doubt has been raised about the level of scrutiny the records were subject to (Collar et al. 1999). The green racquet-tail's decline is thought to be similar to that of many other parrots of the Philippines: it was common several decades ago but has become very rare recently as a result of deforestation and collection for the pet trade (Poulsen 1995; Snyder et al. 2000). However, Kennedy et al. (2000) stated that the decline of green racquet-tail may be less straightforward because it appears not to be heavily subject to the pet trade or to deforestation. The parrot pet trade in the Philippines has had a tremendous negative impact on certain species. The most notable example is the Philippine cockatoo (Cacatua haematuropygia), which at one time was widespread throughout the Philippines but is now scarce (if not extinct) in Luzon, an enormous decline caused almost entirely by the pet trade (Snyder et al. 2000).

Table 2. Endemic and Near-Endemic Bird Species.

  Family Common Name Species
Turnicidae Spotted buttonquail Turnix ocellata
Turnicidae Luzon buttonquail Turnix worcesteri
Rallidae Brown-banded rail Lewina mirificus
Columbidae Luzon bleeding-heart Gallicolumba luzonica
Columbidae Whistling green-pigeon Treron formosae
Columbidae Flame-breasted fruit-dove Ptilinopus marchei
Columbidae Cream-breasted fruit-dove Ptilinopus merrilli
Psittacidae Luzon racquet-tail Prioniturus montanus
Psittacidae Green racquet-tail Prioniturus luconensis*
Cuculidae Red-crested malkoha Phaenicophaeus superciliosus*
Cuculidae Scale-feathered malkoha Phaenicophaeus cumingi
Cuculidae Rufous coucal Centropus unirufus
Strigidae Luzon scops-owl Otus longicornis
Strigidae Ryukyu scops-owl Otus elegans
Bucconidae Luzon hornbill Penelopides manilloe
Pittidae Whiskered pitta Pitta kochi
Campephagidae Blackish cuckoo-shrike Coracina coerulescens
Turdidae Ashy thrush Zoothera cinerea
Timaliidae Luzon wren-babbler Napothera rabori*
Timaliidae Golden-crowned babbler Stachyris dennistouni
Timaliidae Chestnut-faced babbler Stachyris whiteheadi
Timaliidae Luzon striped-babbler Stachyris striata*
Sylviidae Philippine bush-warbler Cettia seebohmi
Sylviidae Long-tailed bush-warbler Bradypterus caudatus
Sylviidae Grey-backed tailorbird Orthotomus derbianus
Muscicapidae Rusty-flanked jungle-flycatcher Rhinomyias insignis
Muscicapidae Ash-breasted flycatcher Muscicapa randi
Muscicapidae Furtive flycatcher Ficedula disposita*
Muscicapidae Blue-breasted flycatcher Cyornis herioti
Muscicapidae Luzon redstart Rhyacornis bicolor
Monarchidae Short-crested monarch Hypothymis helenae
Monarchidae Celestial monarch Hypothymis coelestis
Pachycephalidae Green-backed whistler Pachycephala albiventris
Paridae White-fronted tit Parus semilarvatus
Rhabdornithidae Long-billed rhabdornis Rhabdornis grandis
Dicaeidae Flame-crowned flowerpecker Dicaeum anthonyi
Zosteropidae Lowland white-eye Zosterops meyeni
Estrildidae Green-faced parrotfinch Erythrura viridifacies
Oriolidae White-lored oriole Oriolus albiloris
Oriolidae Isabela oriole Oriolus isabellae*

An asterisk signifies that the species' range is limited to this ecoregion.

The Philippine eagle is the national bird of the Philippines and the most famous animal in the country. Unfortunately, the eagle is critically endangered, existing in primary lowland forests of Samar, Leyte, Mindanao, and Luzon. The large area needs of the eagle coupled with the bird's low reproductive rate have made it highly susceptible to deforestation. The two largest remaining populations are in Luzon and Mindanao, although precise numbers of individuals are still speculative. Population numbers are estimated mainly by assumptions of remaining forest cover, range size, percentage occupancy, and the number of immature birds that territories include. Luzon is thought to have between 52 and 104 eagles, but probably around 78 (Collar et al. 1999). The survival of the Philippine eagle is being watched as a benchmark of the health of the Philippines environment as a whole. The survival of the species is largely tied to the protection of the few remaining large tracts of forest. Such protection would benefit many other forest-dwelling species.

Current Status
The largest remaining forested area in the ecoregion is in the lowlands of the northern Sierra Madres, which have remained inaccessible. The Northern Sierra Madre Natural Park (also know as the Palanan complex or wilderness) has recorded most of the ecoregion's endemic bird species and is a stronghold for the long-tailed macaque, Philippine warty pig, and Philippine brown deer. Luzon's population of Philippine eagles is joined by thirteen other threatened bird species. The park receives funding and attention from the Department of Environment and Natural Resources (DENR), several conservation organizations, the Global Environment Facility, and the European Commission. However, the park is threatened by plans to construct roads that would transect the park and is subject to high levels of encroachment (several towns are within the park boundary). Other sites, which include lowlands in the northern Sierra Madres and have been identified as important areas for biodiversity, include Mt. Cetaceo and Mt. Los Dos Cuernos. Neither of these sites receives any formal protection, and both are being cleared (Collar et al. 1999).

As noted earlier, Mt. Isarog National Park (table 3) is of major importance for endemic mammals. Mt. Isarog also contains four threatened bird species. The national park status of the Mt. Isarog has not effectively protected it thus far. Encroachment on the park has led to a population of several hundred people who live in the park. Also, deforestation continues at the hands of "well-financed commercial ventures" (Collar et al. 1999, p. 57; see also Heaney et al. 1999 and Heaney and Regalado 1998). However, the Haribon Foundation does have an active conservation program at Mt. Isarog that is again gaining strength.

Table 3. WCMC (1997) Protected Areas That Overlap with the Ecoregion.

  Protected Area Area (km2) IUCN Category
Paoay Lake 7 III
Cassamata Hill 40 V
Northern Luzon Heroes Hill 110 III
Lake Malimanga 6 IV
Subic-Bataan Extension 90 PRO
Bataan 310 II
Roosevelt 20 V
Biak-na-Bato 60 V
Hinulugang Taktak 2 III
Quezon National Park 30 III
Mts. Palay-Palay-Mataas Na Gulod 40 II
Fugo Island 140 V
Palaui 90 V
Magapit 90 IV
Penablanca 120 V
Callao Cave 8 V
Northern Sierra Madre 260 II
Fuyot Spring 30 III
PNOC 1636 [IM0122] 1,060 ?
Mts. Banahaw San Cristobal 30 II
Taal Volcano 20 III
Bicol 30 II
Quezon National Park 10 III
Libmanan Cave 20 III
Catanduanes 270 PRO
Caramoan 30 III
Bulusan Volcano 50 II
Manlelung Spring 5 III
Minalungao 1 V
Capas Death March Monument 1 III
Mt. Arayat 80 V
Aurora Memorial 120 V
Mt. Isarog 150 II
Mayon Volcano 80 III
Total 3,410  

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

The smaller islands in the ecoregion have not fared well. Marinduque contained only 317 ha of primary forest in 1992, compared with 813 ha in 1984, for a loss of 61 percent (Development Alternatives 1992). The current amount of primary forest on the island is unknown. Early this century, Polillo was so forested that McGregor wrote that "he had never seen an island with 'so large a proportion of the area covered with trees,'" but today no forest remains (McGregor 1910 quoted in Collar et al. 1999, p. 55). Forest cover maps from 1992 showed that Catanduanes contained some forested areas. Central Catanduanes is listed as an important area for biodiversity, but it currently receives no protection (although it is a proposed watershed reserve) (Collar et al. 1999).

Types and Severity of Threats
There are no recent estimates of primary forest cover for the Philippines. Originally 95 percent of the Philippines was covered by rain forest (Heaney and Regalado 1998). Intact lowland forest made up less than 6 percent of the total land area of the country about a decade ago, with another 12 percent being classified as degraded (Collins et al. 1991). From these figures, the state of the forest in the Philippines could be the poorest in all of tropical Asia (Poulsen 1995). In the intervening decade, more forest has been cleared as a result of unsustainable shifting agricultural practices, legal logging, and illegal logging. These threats are still present and are the main future threats to biodiversity, followed by unsustainable hunting and collection for trade.

The Luzon Rain Forests [IM0123] ecoregion has been greatly modified by human activities. This is probably unavoidable given the high rate of population increase and the size of the population as a whole. Three of the country's largest cities are in this ecoregion: Manila, Quezon City, and Caloocan City. Many of the lowland areas were converted into agriculture long ago, but recent forest clearing is a tremendous problem. Still, Luzon's estimated 24 percent total forest cover was and probably is better than that of the Philippines as a whole. This is probably because Luzon has smaller trees than the rest of the country because of increasingly frequent typhoons in the northern Philippines (Collar et al. 1999), rugged mountains, and independent ethnic communities.

Justification of Ecoregion Delineation
MacKinnon (1997) identified seven subunits in the Philippines, and the Philippine Biodiversity Action Plan (Philippine BAP 1997) demarcated fifteen biogeographic units. Udvardy (1975) identified the Philippines as a single biogeographic province. We delineated nine ecoregions in the Philippine islands, including Palawan. We deviated from Udvardy (1975), MacKinnon (1997), Stattersfield et al. (1998), and the Philippine BAP (1997) to varying degrees and based our delineation of the Philippine ecoregions primarily on Heaney (1993).

In Luzon we delineated three ecoregions, which correspond to MacKinnon's subunit 26a. First, we used the 1,000-m contour from the DEM (USGS 1996) to delineate the montane forests from the lowland forests. The Luzon Montane Rain Forests [IM0122] are made up primarily of the montane moist evergreen forests along the Sierra Madre, northern Central Cordillera, and Zambales mountain ranges. MacKinnon (1997) shows an area of freshwater swamp forests as part of the original vegetation of Luzon Island, which we combined with the remaining lowland forest of Luzon to form the Luzon Rain Forests [IM0123]. These freshwater swamps, in the valley to the east of the Zambales Mountain Range and in the Cagayan river plains, have been converted to rice fields (D. Madulid, pers. comm., 1999). Following Stattersfield et al. (1998) and Dickinson et al. (1991), we placed the Lubang Islands and Batanes and Babuyan groups with the Luzon Rain Forests [IM0123]. The Banguet pine (Pinus insularis, also known as P. kesiya)-dominated conifer forests in the Central Cordillera were designated as the Luzon Tropical Pine Forests [IM0302].

References
References for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.
Indo-Pacific Reference List

Prepared by: John Lamoreux
Reviewed by:

 

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