Introduction

Sierra Madre Mountains, Philippines. (Source: Photograph by Jorgen Thomsen / Conservation International)

The ecoregion has suffered from human exploitation but still contains some of the most extensive forests left in the Philippines. Therefore, the montane forests are extremely valuable for the wide range of endemic species they support and for their role in preventing soil erosion and protecting water quality. It is one of the biologically least known ecoregions in the Philippines.

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 Luzon Montane Rain Forests ecoregion comprises the high elevations of several mountain ranges including the Northern and Southern Sierra Madre, which parallels the northeastern coastline of Luzon. Also included in this ecoregion are Mt. Sapocoy, Mt. Magnas, and Mt. Agnamala in the northern Central Cordillera and the Zambales Mountains in the west.

The geologic history of the Philippines is very complex and has had tremendous influence on the biota found there. Luzon has developed many unique species of plants and animals 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 is therefore oceanic in character, having never been connected to mainland Asia. Even during the Pleistocene, as world sea levels fell 120 meters (m), Luzon expanded to become a larger island including the modern islands of Polillo, Marinduque, and Catanduanes but never connected to other regions of the Philippines or to mainland Asia.

Mt. Isarog, Luzon, Phillippines. (Source: Photograph by L. Heaney)

Annual rainfall in the ecoregion can be as high as 10,000 millimeters (mm) in some areas, or about quadruple what the Luzon Rain Forests receive. When the rain falls, varies with the mountain ranges. The Sierra Madres are only mildly seasonal, with a dry period occurring from December to April. The mountains of the northern Central Cordillera and the Zambales Mountains are more strongly seasonal, receiving a bit less rainfall and having a longer dry period. These forests are also affected by typhoons that sweep across the South China Sea, hitting the western side of Luzon every few years. These typhoons are a major element of disturbance.

The montane forests of this ecoregion begin at about 1,000 m and are characterized by the appearance of oak and laurel species. These trees gradually replace the dipterocarp trees that dominate at lower elevations. The oaks and laurels do not have the wide buttresses of lower-elevation trees. Montane forests in general are shorter in stature than lowland forests and have less undergrowth. Epiphytes and vines (particularly pandans of the genus Freycinetia) and moss-covered branches are very common in the montane forests. The decreased temperature that accompanies increasing elevation slows the decomposition of debris. This makes the forest floor thick with humus.

The highest elevations of the montane forests sometimes are called upper montane forest or elfin forest. These forests are not treated as a separate ecoregion; rather, they are considered montane forests in extreme. Tree branches appear to be many times thicker than they actually are because the moss covering the branch is so thick. Tree height may be only a few meters, and plants that are not typically epiphytes become aerial because of the thick moisture and abundant organic material on and around trees here. Many of the endemic animal species of the Philippines are found as burrowers in the matty soil of this high-elevation forest.

Biodiversity Features

The Luzon Montane Rain Forests ecoregion has eight species of near-endemic mammals and one species that is strictly endemic (Table 1). The strictly endemic Palanan shrew-mouse, Archboldomys musseri, is known only from two specimens taken at about 1,650 m from Mt. Cetaceo in the northern Sierra Madres. Species listed as threatened (VU or above) include three near-endemic species: Luzon pygmy fruit bat (Otopteropus cartilagonodus), Luzon short-nosed rat (Tryphomys adustus), and long-nosed Luzon forest mouse (Apomys sacobianus).

Five relatively 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 The World Conservation Union (IUCN). 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.

The ecoregion contains twenty-eight near-endemic bird species and no strict endemics (Table 2). At least eleven threatened bird species (IUCN categories VU and above) occur in the ecoregion, and two others may be present, but their distributions are poorly known (brown-banded rail [Lewinia mirificus] and Luzon buttonquail [Turnix worcesteri]). Whiskered pitta (Pitta kochi) is a species typical of mossy montane forests and is listed as vulnerable. Whiskered pittas usually are found above 1,000 m in the Sierra Madre and Central Cordillera among oaks, 5-12 m high, with a fern and rhododendron understory. They hunt for invertebrate prey on the ground and are known to regularly forage where Philippine warty pigs have rooted over the soil and exposed prey. The bird is sometimes described as uncommon to rare, although in appropriate habitat it may actually be quite common. This discrepancy probably results from undersampling (and general lack of knowledge) of habitat throughout the pitta's range.

Another vulnerable species, typical of montane forests, is the flame-breasted fruit-dove (Ptilinopus marchei), a beautiful bird with a crimson orange breast and matching crown. It is the largest fruit-dove in the Philippines, and although it has probably always been uncommon and local, it appears to be particularly sensitive to the threats facing much of the ecoregion's biodiversity. The fruit-dove is not found in areas highly susceptible to habitat destruction, found in neither logged nor selectively logged areas. The fruit-dove is also hunted for food and the pet trade.

Current Status

There are no recent estimates of primary forest cover for the Philippines. If one adds the total forest cover for the provinces containing the bulk of the ecoregion, about 482,000 hectares (ha) of forest remained in 1992. A small portion of the ecoregion's montane forest occurs outside these provinces, yet the overall figure is still too high because much of the forest is below 1,000 m. More importantly, the figure is too high because the amount of forest has declined a great deal since 1992. We know this because forest cover for the same provinces totaled more than a million hectares in the early to mid-1980s, for a decline of 55 percent since 1992, and deforestation has continued, with some slowdown since 1994 (figures based on 1981 and 1984 data, depending on the particular province).

The two largest remaining forested areas in the ecoregion are in the montane portions of the northern Sierra Madres, which have remained inaccessible, and the northern Central Cordillera. The Northern Sierra Madre Natural Park (also known as the Palanan complex or wilderness) is the main focus of conservation in the region, although the park covers only the lowland portions of the forest and should be extended to incorporate the higher elevations as well (Table 3). Other sites in the northern Sierra Madres that 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. Recent field work in the northern Central Cordillera has documented extensive forest managed by the traditional cultural groups. Nearly unknown biologically until recently, it is now suspected of being one of the biologically richest and most important areas in the country.

Types and Severity of Threats

Habitat conversion is the primary threat to the ecoregion. Commercial logging (both legal and illegal) continues to have a devastating effect on biodiversity. Conversion of highland areas to "large-scale plantations is currently expanding, causing both displacement of subsistence farmers (who then move further upslope) and increased erosion, which is already a serious problem".

New roads and mining projects directly threaten forests but also make forests more susceptible exploitation as a result of increased accessibility. Subsistence hunting and capture of species for a growing wildlife pet trade adversely affect many of the ecoregion's species.

Justification of Ecoregion Delineation

MacKinnon identified seven subunits in the Philippines, and the Philippine Biodiversity Action Plan 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 et al., and the Philippine BAP to varying degrees and based our delineation of the Philippine ecoregions primarily on Heaney.

In Luzon we delineated three ecoregions, which correspond to MacKinnon's subunit 26a. First, we used the 1,000-m contour from the Department of Environmental Management (DEM) to delineate the montane forests from the lowland forests. The Luzon Montane Rain Forests are made up primarily of the montane moist evergreen forests along the Sierra Madre, northern Central Cordillera, and Zambales mountain ranges. MacKinnon showed 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. 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. Following Stattersfield et al. and Dickinson et al., we placed the Lubang Islands 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.

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