Luzon rainforest

• Category: Forest Biomes.
• Geographic Location: Philippines.
• Summary: A tropical rainforest that is home to a highly diverse range of flora and fauna, this biome includes a large number of endemic species, but faces significant threats from human activities.

On the western flank of the Pacific Ocean lies the Philippine archipelago, a cluster of 7,107 islands. The largest of these is Luzon, a 40,400-square-mile (104,700-square-kilometer) mosaic of highly developed urban areas and primary rainforest. Geographic isolation and a tropical climate have resulted in high biota diversity levels, with a significant number of endemic (found nowhere else) plant and animal species. Illegal logging, development encroachment, and other human activities pose significant threats to this biome’s conservation prospects.

Geography and Climate

Luzon, an irregularly shaped island at the northern end of the Philippines, has an uneven terrain. Two mountain ranges, the Cordillera and the Sierra Madre, run north and south on both sides of the Cagayan River, the country’s longest. Isolated volcanic mountains above 3,300 feet (1,000 meters) break up the flat areas on the southern portions of the island. These are Mt. Banahaw, Mt. Makiling, Mayon Volcano, Mt. Isarog, and Mt. Bulusan.

The island’s tropical climate has a relatively high average temperature of 80 degrees F (27 degrees C), high humidity at 70–90 percent, and abundant rainfall of 40–200 inches (102–508 centimeters) yearly. Three main seasons are influenced by equatorial monsoons: hot and dry (March to May), rainy (June to November), and cool and dry (December to February). Although some areas may experience torrential rains during typhoons, variations in temperature and rainfall occur mainly due to elevation and proximity to bodies of water.

Flora and Fauna

The Luzon Rainforest biome is composed of tracts of moist dipterocarp forests in areas below 3,300 feet (1,000 meters), as well as on islets north of the main island and the handful of volcanoes in the south.

Dipterocarps are hardwoods named for their two-winged seeds, which spin like helicopter blades as the seeds fall to the ground. These broadleaf trees rise as high as 200 feet (61 meters), with straight trunks stabilized by wide buttresses, and sometimes stilt roots, for extra support in the shallow soil.

Additional adaptations to the environment include smooth thin barks that require no protection against freezing or water loss; and drip tips, grooved leaves, and oily coatings that allow leaves to quickly shed water, preventing mold and mildew growth. Common genera in the Luzon Rainforest include Shorea and Dipterocarpus.

The canopy tends to be uneven, making the emergent or highest layer practically non-existent, and the lower understory rich in flora such as rattans, woody lianas, saplings, large ferns, and strangler vines climbing toward sunlight. Mosses, orchids, bromeliads, and other epiphytes flourish on tree branches, making the most of the available light, water, and nutrients.

The unique flora of Luzon is exemplified by the Philippine jade vine, a woody climber that produces striking blue-green flowers. The jade vine is endangered in the wild, but has been successfully cultivated through cuttings in conservatories, botanical gardens, and private gardens all over the world. The difficulty in propagating the plant from seed is due to its need for bat pollinators, which are themselves sensitive to the effects of deforestation and habitat loss.

The forest floor, which receives as little as 1 percent of the sunlight that falls on the canopy, is host to plants and animals that thrive in the cool, shaded environment. Mushrooms and other fungi, worms, ant colonies, termites, and small animals facilitate the breakdown of leaf litter and other organic matter, releasing the nutrients for immediate use by surrounding plants. The short cycle of breakdown, release, and absorption results in low nutrient content and poor quality of the rainforest soil.

The Luzon Rainforest supports a number of highly diverse bird species, 40 of which are either nearly or strictly endemic to the area. Two threatened species of note are the green racquet-tail, which is also found on Marinduque, and the Isabela oriole, once thought extinct, which is endemic to Luzon. In addition to habitat destruction and deforestation caused by illegal logging, an unchecked pet trade has caused the decline not only of the Isabela oriole, but also a number of parrot species, such as the Philippine cockatoo.

The critically endangered Philippine eagle, the country’s national bird and most famous conservation symbol, includes the Luzon rainforest in its habitat zone. The species requires large areas of primary forest to thrive, and depends on the protection of remaining rainforests to avoid extinction in the wild.

The Luzon Rainforest biome contains fifteen species of strictly endemic and near-endemic mammals, including three shrew-like animals found only on Mt. Isarog, and one identified through a single specimen from Sierra Madre. Thirteen mammal species are considered threatened. Among them is the fruit-eating golden-crowned flying fox, which is possibly the largest bat species in the world. The bat is threatened by hunting, the animal trade, and loss of habitat. Five large mammals live in the biome, including a macaque, warty pig, and civets; none of which are listed as threatened, but all are still vulnerable to habitat destruction.

Human Impact

The highly diverse flora and fauna of the Luzon Rainforest ecosystem are threatened by human activities such as illegal logging, the pet trade, conversion of primary forests for agricultural use, and increasing urban sprawl. Deforestation has drastically reduced the forest. The country has lost a third of its forests cover since 1990. Although many areas that overlap the biome have been given protection as natural parks—totaling approximately 1,320 square miles (3,400 square kilometers)—these parks are scattered throughout the island, with some covering 10 square miles (26 square kilometers) or less.

In addition to natural park status, inaccessibility appears to be the main contributing factor for successful conservation of the rainforest, as in the case of the Palanan wilderness in the Northern Sierra Madre. Palanan is the largest swath of forested area in Luzon and a refuge for many threatened species, including the Philippine eagle. It is facing the prospect of greater encroachment amid the planned construction of roads within the park.

Strict enforcement of designated protected areas, community education and involvement, and reduced incentives for commercial logging and clearing of forests are needed for effective conservation of the few remaining primary forests in this highly diverse but also significantly threatened biome. Protection will also be needed from the looming pressures caused by warmer temperatures and sea-level rise due to global climate change. It is predicted that there will be more frequent and more severe storms in this region, which could erode soils and accelerate habitat fragmentation.

Bibliography

Corlett, Richard and Richard Primack. “Dipterocarps: Trees That Dominate the Asian Rain Forest.” Arnoldia 63, no. 3 (2005).

Newman, Arnold. Tropical Rainforest. New York: Checkmark Books, 2002.

Pang, Sean E.H., Jose Don T. DeAlban, and Edward L. Webb. "Effects of Climate Change and Land Cover on the Distributions of a Critical Tree Family in the Philippines." Scientific Reports, vol. 11, 2021. DOI: 10.1038/s41598-020-79491-9. Accessed 12 Nov. 2024.

Wikramanayake, Eric, Eric Dinerstein, Colby J. Loucks, et al. Terrestrial Ecoregions of the Indo-Pacific: A Conservation Assessment. Washington, DC: Island Press, 2002.