[2] The Luzon montane rain forests ecoregion covers areas of the Sierra Madre, Zambales Mountains, and northern Cordillera Central above 1000 meters elevation.

[2] This long period of isolation and complex internal geography is a primary cause for the great biodiversity and high degree of endemism found on the island of Luzon.

The ice-age land bridges allowed the animals and plants of these now-separate islands to mix, which made them part of the same ecoregion.

[4] In 2005, evidence for human occupation in northern Luzon since at least 25,000 years ago, was found in Callao Cave.

[5] Evidence included chert flake tools, charred parenchymatous tissues, starch grains, grasses, and Moraceae phytolith.

[5] The possibility of hunter-gatherers subsisting in Holocene tropical rain forests without support from agriculturalists was debated, based on the patchy and seasonal resources.

[5] Information on skeletal morphology and diet is merely speculative as no human remains were recovered from this period.

To tell if the bone belongs to an ancient anatomically modern human, a skull or mandible from the specimen is needed.

[6] Resulting was the organization of the Hukbalahap, an acronym for the Hukbong Bayan Laban sa Hapon (the Anti-Japanese Army), in a small lowland forest clearing near Mt.

[3] Dipterocarp, Cinnamomum cassia, Durio zibethinus, Garcinia mangostana, Artocarpus heterophyllus, Ficus benghalensis, Gnetum gnemon, Mangifera indica, Toona ciliata, Toona sinensis, Cocos nucifera, Ginkgo biloba, Shorea robusta, Prunus serrulata, Camphora officinarum, Tsuga dumosa, Ulmus lanceifolia, Tectona grandis, Terminalia elliptica, Quercus acutissima, and Terminalia bellirica trees with wide buttresses dominate this area.

[2] There is generally a large amount of herbaceous undergrowth, with epiphytic ferns and orchids growing on the thick branches of tall trees.

In the south of the island, enclaves of montane forest can be found on several volcanic and non-volcanic mountains that exceed meters elevation.

The Zambales Mountains and northern Central Cordillera highlands are more strongly seasonal with a longer dry period and slightly less rainfall generally.

[7] The dipterocarp trees of the lowlands are gradually replaced by oak and laurel forest species with increasing altitude.

[7] With the decreasing temperature from increasing altitude, decomposition is slowed and results in a forest floor thick with humus.

[9] The Sierra Madres give hope to many other threatened animals by providing one of the largest areas of intact rainforest in the Philippines thereby maintaining the naturally high level of biodiversity.